ROIDING THE EXTREME.


WARNING:

This exercise will most definitely void any warranties either express, implied or mandated within individual state or national jurisdictions. The modification also introduces greater risk of impact damage as two protections provided by the manufacturer are removed.

Furthurmore, this exercise requires advanced home engineering skills and workshop equipment.

This includes accurate drill-press, in the case of my modifications - 2.5mm diam drillbits, a Dremel precision tool or similar, glass and lens cleaning kits, 3mm tapered thread taps and suitable grubscrews or other threaded stock to cut down to shape and size.

Screws and thread taps identical to Letus original fitments should be substituted if they can be obtained.

Machine screws with protruding heads should not be substituted for concealed grub screws as accidental impact on the screw heads during use or shipping will almost definitely chip or crack the prisms.


INTRODUCTION:

At time of writing, the Le brothers' penultimate offering to the 35mm groundglass based relay adaptor market is the Letus Extreme. At the time it was released it was their most mature version, since supplanted by the Letus Ultimate.

The components of the Extreme have been made to sizes and tolerances which provide coverage of an adequate groundglass area for relay of an image, reasonably but not exceedingly larger than the standard motion picture film frame of 24mm x 18mm.

The available oversize groundglass area is much larger and closer to still-image film camera frame size. It is apparent that it is not intended to provide this size of image, but to allow for minor variations in fixed alignment consistent with as simplified and robust a construction method as can be devised in order to contain costs for the end-user.

Since the Extreme was released, new high-definition cameras, notably the Sony PMW-EX1 and the Silicon Imaging SI2K have entered the marketplace and the bar has been raised for the alternative adaptor makers and vendors.

The generous available groundglass area of the Extreme and previous Letus models was found to convey higher apparent resolutions when the widest groundglass view permitted by lens-in-camera zoom relay was chosen.

Users of the Extreme on cameras such as the Sony PMW-EX1 began to fret over not being able to centrally frame the Letus groundglass at wider zoom settings to render even higher apparent resolutions that this remarkable camera permits.

This is an application which I believe would not have been an original design intention. At this sought-after zoom setting the fields-of-view are no longer faithful to the 24mm x 18mm motion picture frame.

The Ultimate has provision for x-y-z optical axis adjustment, an obvious response to customer requests. The fixed position of the Extreme's parts and use of a vibrating groundglass does not easily permit the Ultimate style adjustment system.

Due to impact damage from careless handling by another, not me, I was compelled to dismantle an Extreme to remove a very small floating glass chip, fortunately not off a critical position anywhere in the optical path. Whilst I had it apart, I examined the prism system to see if some adjustment could be made available.

I discovered that the prism path consists of three prisms with two smaller prisms permanently bonded to a larger prism with optical cement.

This method minimises construction errors, unwanted internal reflection and dust problems. It represents a considerable step-up in method and sophistication of design by the Le brothers. However, the permanence of this method is at expense of convenient means of adjusting on all axes

The path has been made large enough that there is no need for adjustment for an acceptable groundglass viewing area. The large compound prism is supported on a central spine and cushioned against limited impacts by small thin stick-on pads on the end faces of the enclosure walls adjacent to the larger prism and use of a soft synthetic rubber wedge.

The spine design and compound prism in combination, do not permit the x-y-z adjustments traditionally found in prismatic binoculars. However I found that by adding a little extra space within the enclosure by bringing the cover plate forward by about 0.8mm with shims, enough lateral angular adjustment could be achieved for critical centering of the optical path.


THE METHOD:

Three small grubscrews are used. One each in the end walls near the right-angle corner of the large prism, 10mm in from the inner curved apex of the prism space in the casework, one in centre of the right-angle corner of the large prism.

A full span replacement spacer of polypropolene replaces the rubber wedge and is a protective clamping surface for the centre screw to bed upon. Two rocker pads of stick-on felt sheet are made for the end walls, one small rocker pad for the spine and two smaller impact pads are made to protect the vulnerable corners of the smaller prisms. The rocker pads on the end walls are double thickness to enable clearance of the impact pads otherwise all would bed down together and no adjustment movement would occur.

A thin paper sheet is cut to wrap around the centre spine to tighten vertical alignment and provide a protected sliding surface and two thin end-walls of paper are cut to protect the prism surface from chipping where the grubscrews contact. The ends of the grubscrews must be finished and polished to prevent penetration of the paper and avoid chipping.

By careful tighening and release of the two end grubscrews and then tightening of the centre grubscrew to firm the adjustment, accurate lateral centering can be achieved.

There is risk that the paper layer over the spine, may in time swell with moisture and apply wedging pressure against the optical cement bonds which may fail catastrophically. With time, chemicals in bleach processed paper may adversely affect the contacting surfaces of the glass, however if at all, this will likely not happen until the adaptor is worn out, obseleted and consigned to landfill.

FOOTNOTE TO ABOVE POST :


I dismantled the Extreme again to make some images. Whilst inside I checked the paper end pieces. Despite dry lubing with a pinhead of wax, the paper still tends to pick up on the grub screw-end and tear.

I have now replaced the triangular paper end pieces with pieces of thin brass shim. This has been secured to the end walls with a very thin tack of contact adhesive along the edge adjacent the felt rocker pads.

The paper sleeve I folded over the centre spine, I have replaced with thin clear firm plastic sheet. It is slightly thinner than the paper and will not pick up moisture from the air and swell.

Increased screen area comes at a cost. Fewer digital lenses may work on it when the entire groundglass screen width is chosen. The 12mm - 24mm f4 Nikon zoom vignettes until 18mm zoom-in is reached.


ADDED TEXT.


Here is some vision of the mods done.

http://exposureroom.com/members/DARANGULAFILM.aspx/assets/27cc38a6dcf14c319efb07bb39e69a48/

There is no commentary. Read the clip information while the clip downloads. What I neglected to illustrate was a short strip of felt on the centre spine inside the flip enclosure. This piece is approximately 18mm long and is in centre of the narrow face of the spine. The composite prism rocks on this raised area plus the two pieces of felt on each end-face insude the enclosure. The "rocker" pieces are twice as thick (two layers) as the smaller pieces intended to protect the corners of the smaller prisms.


Please do not attempt this mod unless you have advanced dextural skills, good mechanical facility and home workshop equipment.

Nice work Bob.
How do you clean the prism surfaces? I find it impossible to get no streaks.

Cheers.

Dennis.


Cleaning the prisms? - With great difficulty.

A few clues, most probably wrong :-


1. Clean working environment. (includes oiling or covering one's own hair to prevent fallout onto the glassware and oil the face as well if you are prone to excema or rashes.) Wash hands thoroughly to remove oils from fingerprint treads.

2. An operating CRT or mozzie zapper operating nearby may help collect dust if the climate is dry.

3. When removing the prism as I did, use tissue or clean soft cloth to avoid skin contact and hold matte-finished surfaces only. Dusty lint will come off but this is more easily brushed than oily fingerprints.

4. I found there was some surface grease on the inner surfaces of casework, possibly there to immobilise swarf and dust.

5. When handling the compound prism, avoid finger contact with interior casework surfaces or the corners where the front cover goes on. There may be oils there which will cross over onto the glass on your fingertips.

6. Clean fingertips with soap and water frequently and dry off properly during the whole operation.

7. Clean the grease from the internal surfaces of the casework with a solvent. Some owners have relaid a grease surface to trap any future dust. I chose not to. I also chose not to paint the internal surfaces - what is good enough for prismatic binoculars is good enough for me, though maybe not optimum.

Because you likely will have left the motor wiring intact, the only practical method for shifting the grease will be cotton swabs and large metal tweezers, medical style. You will need to brush out the cotton fibres afterward as they will hang on machining burrs.

8. Cleaning glass surfaces :-

The most likely contaminent will be some oil. This is a dog to get off and will get into your lens cloth and come back on the surface you are cleaning. This is why you need more than one lens cloth.

Accepted method of cleaning optical glass is to wash with pure soap and clean water. You may need to use some distilled water if your local water is hard and soap does not work.

If the oil or grease is stubborn you may need to use some dishwash detergent to emulsify the grease. Wash off with pure soap and water, then water alone.

Have several purple microfibre lens cleaning cloths and lens brushes handy. The microfibre cloths are really the absolute best for final polish off so don't be cheap. Buy some. The brushes on lenspens are fine for flicking off specks which fall back on but be aware that the lenspen brushes are not capped and may themselves become contaminated after you have opened the retail packs and used them.

If you get a new smear from a cleaning cloth, it will have to be washed. If you have left grease on the internal surfaces, chances are when you have that final clean-up after assembly, you will pick up a pinpoint of grease from a corner and bring it back onto the prism.

People use wood alcohol (methylated spirit) for cleaning glass. I find that it leaves some stubborn residues which the purple lens cloths do not always remove. You may need to rewash or simply breath onto the glass and polish off the condensation.

It is long, tedious but achievable.


If you are going to do the grubscrew thing, I cannot emphasise enough that the glass surface must be protected against direct contact with the ends of the grubscrews. Stress risers already exist in the contact zone from a ground finish on the prism sides.

This protection could be thin clear hard plastic like shirt collar straps from retail packs or more better, brass shim material which your performance auto accessory retailer should be able to find.

Cheers for that Bob... it's a damn mission getting them clean!

If you think this is tough, take on a pair of old prismatic Bausch & Lomb binoculars which have been swimming at some point in the history. As a jack-of-all-trader, I attempt many skills but we know how good Jack was at all??

To the real practitioners who have served their apprenticehsips and put in the time - great respect. Cleaning of optical glass would be a task they would have perfected to the point of practiced ease. For the likes of me it remains a difficult and choresome novelty.

This is a sort of cross post. Some grabs of behind scenes footage are here. This was with the Letus Extreme modded for lateral groundglass image centricity. Zoom on the Sony Z1P was backed to about 24mm.

SI2K in Western Australia. - Page 3 - The Digital Video Information Network (http://www.dvinfo.net/conf/showthread.php?p=930473#post930473)

I was a bit careless when framing up with the camcorder zoom so there is a groundglass frame edge just inside the image. I was shooting freehand with no rails attached and allowed the Letus to slip slightly clockwise without observing the error.


Here is an address to a short clip the frame grabs came from :-

http://exposureroom.com/members/DARANGULAFILM.aspx/assets/a12fff28227a449b9aba4ac4a5830b07/


Offtopic. Does anyone know how many watts load a "Markon" generator with Kawasaki 5HP motor should be good for? It is believed to be an overpowered repower, the original motor believed to have been smaller Honda. This one fades off after 30 minutes with a 1000w load. Unfortunately there are no model markings on the generator, just three layers of red paint. It came off a roadside throwout with fuel system full of rust.

Bob, few hours a go I have done some adjustments to my friends Letus extreme hooked on EX1. They have noted that picture is not sharp on right side. They also have problem that you have described, picture is to much on a right side. I have made some improvements in regard to a sharpness but this is still not sharp enough.
1.
So, did you try to correct focal flange distance during your roiding the extreme?
There is a weird effect if you push pins from vibrating mechanism they pop up but they almost never pop up on same place (one of the pins was more pushed inn so I have pull him out to compensate to others but it was very hard to place it where you need it because it acts like vacuum pump, and this one pin is very light to move, and when vibrating is on it moves inn, and changes focal plane distance on right side)
2.
Did you see that on this adapter that you have roided, sharpness of this right side is off or is maybe improved after your mod?
( I have try to make this right side sharper by changing angle left right in EX1 to letus mount, or changing angle of SLR lens left right without slr mount but it was very hard to see any significant improvement)

I am preparing an email with pictures to Le brothers, so I just wanna check with you if you have noted some of this problems. They are most present with wide lenses, at very small f numbers, but you know that.

Igor.


The cups are usually fairly tight in the holes as you observed. One cup might have turned an edge and might be leaking. Another thing sometimes happens when you push them back into their holes and shove the pillar into them afterward. It is easy to push a hole through the cup if you use an object which is too sharp like a jeweller's screwdriver or a roast stick. Sometimes the cup goes in a bit sideways and the pillar can get in between the cup and the side of the hole.

You usually feel a distinct tiny thump as you push when the pillar goes back inside the cup correctly. If the cup is damaged and not binding in the hole or it has gone side-on and the pillar is jammed down one side, the pillar may creep as you suggest. If the cup is damaged you might be able to find a close match for it at your local pharmacy in a diabetic syringe.

If you are bending the optical axis at the camera ring to Letus junction by mounting it a bit crooked, (skewing the mount ring) you might be adding distance in the camcorder to groundglass path on one edge.

You can easily check to see if the groundglass is square-on by pointing the Extreme at a plain wall closing the aperture on the SLR lens and checking the texture of the groundglass which should be equally sharp across the image.

If you are trying to make the groundglass square-on to the camera after you have skewed the mount ring to center the groundglass frame view the camera sees, the groundglass will no longer be square-on to the true optical axis of the SLR lens.

The rear face of the cylinder of the lens mount usually has three little screws. They do not hold anything together. They are just there as adjustable spacers. To prop the mount forward a little you screw these out so that the heads butt against a face inside the front of the Extreme when you put the mount back in.

By screwing one a little furthur out, you can skew the mount cylinder so that the groundglass becomes square-on to the SLR lens axis again.

I have to go out right now so cannot reply in more detail than I have. I'll have a think about an easier solution than driling holes and putting more screws in.

I did not observe any soft edge on one side after I centered the prism but I might have got lucky.

Bob,
I have manage to push cups in their holes to the bottom and they was on their sticks(I was affraid to remove rubber cups from sticks...). I have use very thin cooper wire, first I have made a u shape from wire and placed it inside a hole, then I have pushed rubber cup with pin inside. I have removed wire after that. Wire keeps air going out when you pushing sticks in and vacuum keeps them in place, but in this position I was unable to find focus on wide angle lenses at all. I have pull sticks out a little measuring their distance from letus body to slr side of gg holder to be exact the same on all three sticks and find out that around 9mm is good enough to focus with wide lenses.

I will try to find those tree screws for adjusting ffd and try to correct it to match marks on slr lens.

I am suspecting that if picture is to much on a right side, and letus gg is much wider then regular 35 size gg that we actualy see part of picture that is over the edge of 43mm circle that SLR lens display at this much wider gg. I will try to put some paper mark in the middle of gg to see what we actualy see, and also mark real 35mm gg size on left and right.

Igor.


Do not be afraid to pull the cups off the pillars. It is really so much easier to push the cups in first with something like a blunt ended satay stick, then push the pillars in afterwards. A wire loop will either slice a groove in the side of the cup or fold it over. This may be why one is moving.

If you want to draw the groundglass forward, I found the most precise way was to grab each pillar with good metal tweezers, use a wooden roast stick (skewer) as a lever, put the end of the lever on the metal near the condenser lens and lever forwards with the shaft of the skewer against the tweezers.

You still have to allow for the stretch and rebound of the rubber cup but you no longer have to worry about the stretch of the grommets on the groundglass panel itself.

The long wooden skewer gives you much more fine control. I used vernier calipers to make sure the distance between the front of the prism case near the condenser lens and the groundglass is exactly the same at each of the pillars.

One day when I am not so lazy, I will measure the difference between the best position of the groundglass panel and the rearmost position when the cups are pushed in all the way and punch out some small shims to put in the bottom of the holes the cups go into.

When you put the front tube back on, make sure it is firmly back all around before you tighten the four screws.

Last weekend I shot some footage of Bob Grimstead practicing some moves for the upcoming R e d B u l l air race in Perth during which he will fly an acro display with a Fournier RF4 motor glider powered by a 35HP Volkswagen engine. I have posted it for technical interest.

BOB GRIMSTEAD PRACTICES DERRY TURNS FOR A NEW ROUTINE FOR AIR DISPLAY. By Bob Hart On ExposureRoom (http://exposureroom.com/members/DARANGULAFILM.aspx/assets/3f9fccb0021e47e494afea93cd2535f0/)

In this instance, the objective was to try to observe the control inputs and reactions of the aircraft. I needed to get as close as I could with the avalable glass I had and resolution was of secondary importance. So the camcorder relay zoom was right in as was the Sigma for Nikon 50mm-500mm f4 - f6.3 zoom on front.

Blue skies do not always make ideal backgrounds for groundglass work. There's one or two stains in the image where I left some marks on glass after cleaning the prisms. These should not be taken to represent the normal state of the optical path in a new adaptor.

Interestingly, when observing the propellor disk on ground and in the air with a 1/60th sec shutter. I expected to see a severe rolling shutter artifact on the EX1 image. There is none.

Sony must have a trick or two up their sleeve relating to the CMOS sensors and downstream processing of the image.

I must play with this camcorder/adaptor combination some more when opportunity permits.

Call it obsessive compulsive or whatever.

When doing some improved cleaning of the groundglass I had only done roughly after my previous intrusions, I decided to check the available width of the prism path versus the available width of image permitted by the frame of the rectangular condenser in the Extreme.

Here follows my customary warning against people burrowing into the innards of their Letus Extremes and trying any of the indulgent trickery I have been permitting myself. Good workshop skills and machine tools are required for this exercise. Warranties will most definitely be voided and there is a risk of failure and permanent damage.

I found I could gain another 2mm or so of image width by widening the rectangular condenser port in the front of the prism enclosure by milling back the vertical sides (sides of frame) to the same depth of the horizontal support shoulders and dressing back the sides of the contoured plastic support to match.

After re-centering the path to a PMW-EX1 camera, it seems that a satisfactory frame can be had with the camcorder zoom set half-way between 25mm and 40mm on the zoom ring. The zoom can be widened back a little more, however gray side brightness falloff begins to become apparent as the sides of the prism path itself begin to get close.

The field-of-view presented to the wider groundglass view by a 50mm lens on front is nearly that of a 35mm to a framing on the groundglass close to the motion picture frame of 24mm. There do not seem to be any signs of sharpness falloff into the corners and brightness seems to remain consistent across the larger area.

I doubt the slightly wider field-of-view will enable a Nikon 35mm f1.4 prime lens to be used for relay into a SI2K, but that is the next experiment when opportunity permits. A 50mm may be reliably usable.

The vertical lines of the "A" block on a Lemac chart can be seen in the image. The chart notes suggest this block represents 1920 lines of horizontal resolution.

The notes however also suggest that HD video cannot resolve this so maybe a moire pattern is being caused by the vertical pixel rows of the camera.

Short of going the medium format route, there might just be enough sharpness to be had from the widened path of the Extreme to make using it on the SI2K or other 2/3" UHD cameras a viable concern.

I meant to include this in the preceding post but forgot.


FOOTNOTE:

Here is an image made with the Extreme framed closer to motion picture frame width and a Peleng 8mm f3.5 fisheye on front. I only recently discovered the Nikon adaptor I had on back of the Peleng was about 0.2mm off for backfocus. Fixing that with shims has resulted in a major improvement.

For the plane junkies, the aircraft is a Savannah Ultralight two-seater. The cam, an EX1 loaner, with Extreme on rails, was sitting on a parcel shelf behind the seats. It was not flown in that position, just put there for a framing check for a project.

Following up on the post above, here are a couple of grabs from the widened field-of-view.

The camera was an EX1. The lens was a Nikon f1.4 50mm at f2.8. The zoom was set at just a trace over midway between 25mm and 40mm. The Nikon lens is approximately 450mm from the chart versus the 1M when using the 24mm wide motion picture frame from the groundglass. This may account for an apparent edge softness in the image as the view to the Nikon lens now seen is wider. The groundglass texture remains sharp to the edges.

I have observed when the focus assist is selected on, that the EX1 sensor is a little noisy with "white" grain with no gain selected on.

The apparent resolution should be discounted by approximately 5% as I am a little tighter on the chart than 16:9

The grabs were exported from Sony XDCAM clip browser to .bmp and converted to .jpg in MSPaint.

I had a furthur short play with the SI2K and the Extreme. Unfortunately, time did not permit me to borrow or cajole the owner into more extensive testing however the initial result is encouraging.

This time the lens used for relay was a 50mm f1.4 Nikon.

With the prism centricity adjustment modification and the condenser port widened, there is no trace of an edge creeping in that I could see. There was also no trace of edge darkening. So there is a little more wider image to be had from the groundglass but the lens choice for relay is not there in the Nikon range.

On a 16mm film camera, at the Super16mm edges, there is a trace of edge vignetting from the condenser port when a 35mm f1.4 Nikon is used for relay so this would defnitely vignette on the SI2K.

If there was such a thing as a 42mm f1.4 lens to be had as a relay, then this might go close to allowing the maximum amount of groundglass image area.

I also mounted it up to the JVC GY-HD111 there with a 35mm f1.4 Nikon lens for relay. It seems to work well enough but I did not study a large image on a monitor, only what I could see on the LCD screen.

This is a frame grab with Nikon 105mm f1.8 lens on the Extreme before the view was widened. The image picks up rivet detail on the wing panels nicely.

Sorry - the upload failed. Seems like I may have clicked the wrong button.

Another try at upload.

Bob,

Is this frame from your jvc + 35mm f1.4 relay + extreme + 105mm f1.8 set up?


Ted

Ted.


That frame grab is from a loaner PMW-EX1 on the modified Letus Extreme but before I widened the available view by about another 2mm.

The 105mm f1.8 field-of-view as you will observe, is quite wide as I chased with the EX1 zoom as much of a wide view off the groundglass as I could get.

It is probably about half-way between standard movie and the field-of-view you get with your medium-format adaptor.

I think it is possible to hit the resolution limit of the JVCs with wide groundglass views. I think your medium format may have already done that.

If I get time on the next music gig, I will try the arrangement on Steve Rice's JVC again to get some grabs. I have some fears about capturing from his camera as it took my computer down last time I tried.

Bob,

Looking at the footage by extreme you hacked onto the SI2k, I wonder why you have to? What is the sensor size of the SI2k? I thought it was big enough for cinematic DOF?

Another thing, since youre talking about the relay setup, I'm tempted to play around with my set up AGAIN, you mentioned that you have used a 35 or 50mm nikon as a relay for the jvc, what power achromat are you placing infront of the 50? or 35? and whats the distance from the achromat rim to the GG?

I have the cinevate and sgpro achromats, what do you suggest should i use? If i use a 20-40 sigma zoom as relay at the widest setting at 20mm, you think this would be better than the 50mm/35mm relay you tested?

I'm after of several results for this test.

a. a shorter rig set up.
b. to achieve a wider or optimum gg area.
c. an approximate or better image resolved compared to the stock 16x.

if you think its not worth experimenting replacing the 16x with a hack relay please advice if it won't achieve those objectives.


Ted

Hello again Ted.


I wouldn't go hacking just yet. The 50mm on the JVC may take you back to the multiplication factor problem of the Minolta lens on the original direct relay Letus. The SI2K is also a single CMOS sensor, not 3 x sensor prism arrangement so the colour fringing problem is not an issue.

I'll test it some more on Steve's camera and see how it shapes up with a proper test chart.

The Letus achromat is the one for the EX1. It works in combination with a special rectangular shaped condenser lens they have had made up. I'll substitute the 4+ and 7+ Century dioptres from the Agus 35s and see how the size of the image/zoom setting compares.

Thanks Bob,

I knew the 50mm had high crop factor as a relay in my first tests, i was apprehensive I was missing something. I had difficulty getting it to record a wide gg area. After fiddling with the combinations, the compromise image i had ended me with a long distance from achromat to gg so much so that the length was the same if i was using the 16x!

I'll wait till you get around to test it again. In the meantime, my life will go back to normal.. hahaha

Thanks again Bpb.


Ted

Ted.


The Sigma zoom I suspect will not be as sharp as the JVC's own zoom lens as a relay.

The prime lenses may only just come up to the sharpness of the JVC's own lens but if they do, then as you require, the whole thing could be shortened.

Another aspect ran past me. I think from memory you are using a HD250 with in-camera flip. The non-flip Brevis and SGPro achromats may be of a higher power than the ones I have used for my own adaptor which were 4+ and 7+.

The Extreme I have been playing around with has the EX1 special achromat which seems to work equally well with the Z1. I think it is in the ballpark of 4+ power. The condenser lens inside the Extreme seems to be fairly powerful. How much this interacts with the achromat, I do not know and would have to pull it apart to find out.

Next time I get hold of Steve Rice's HD100, I'll set it up with the Nikon 35mm, the EX1 achromat and a 60mm x 70mm target and see what happens. My sense is that with only 4+ or so, the non-flip adaptor is still going to be fairly long. If Wayne's or Dennis' achromats are sharp to the edges with your current setup, then the same achromats on a Nikon prime may be okay as the Nikon's front glass is of a smaller diameter and may likely work more inside a sweeter area in centre of the achromats.

Ted.


I forgot to answer your question on why put a 35mm adaptor on the SI2K. I understand that the P+S Technik Pro35 has been used but it is an expensive solution.

I am probably a glutton for punishment but it is for no better reason than it is there to be tried. To achieve similar shallow depth-of-field effects, Super16mm superspeed lenses have to be aquired. With the RED, SI2K and others, there has been a run on these and they are now rare secondhand and expensive. The cupboard on ebay is now quite bare.

I would not use a 35mm adaptor on the SI2K exclusively but only where I wanted the specialty looks of shallow depth-of-field or an exceptionally wide field-of-view like with the 35mm 14mm lenses or the Peleng 8mm fisheye.

As you correctly suggest, the sensible use of Super16mm and good quality 35mm stills primes will be adequate in most cases.

Interestingly, ( I guess this is off-topic) I had another look at the RED post. Their proposed 28K Monstro sensor appears to be purposed to using plate camera lenses. I imagine your back room is full of old plate cameras from past generations at work.

To what purpose one might wonder but my thoughts are that Omni and Imax style immersive theatrical exhibition might make a big comeback if this technology and the means of economically processing and exhibiting the images gets up. Just imagine it in 3D which would be a financial impossibility with film. There is also obvioius military application and I would not be surprised if the 28K became export restricted like much of the infrared imaging technology.

I don't know what is going on but my posts are dumping on first attempt. Here is a quick recall. I'm not writing a second long one.

Tests with a Letus Extreme modified for adjustable centricity and wider groundglass view indicate the following lenses will work as direct relay via the special EX1 achromat.

The lens on front of the Letus was a Nikon f1.4 85mm.

The relay test lenses were mounted to the JVC camera with a Les Bosher Nikon-to-JVC mount adaptor.

The JVC test camera, Les Bosher Nikon-to-JVC mount adaptor, Nikon lenses for relay and Letus Extreme were assembled with care onto the standard Letus rail system. It is not safe for the hardware to be assembled and tested without this support.


Nikon f1.4 50mm. (multiplication factor as with original direct relay).

Nikon f1.4 35mm. (image width roughly comparable with P+S Technik Mini35-400).

Sigma for Nikon f1.8 28mm. (image width roughly comparable with EX1 wide view of unmodified Letus Extreme).

Sigma for Nikon f1.8 20mm. (image width roughly comparable with EX1 wide view of modified Letus Extreme).


The Nikon f1.4 35mm relay image yield, with detail on the JVC set at "normal" suggests an apparent resolution of the "B" block of a Lemac chart which is 862 horizontal lines or better.


This information should not be taken as assurance that these tests can be confidently repeated on your camera and Letus Extreme adaptor without possible damage occurring.

Using these lenses for direct relay should only be regarded as an inferior stopgap until the genuine direct relay lenses from Letus come along.

The 35mm and 50mm lenses have 52mm diameter filter mounts and would require custom bridging rings to mount to the back of the Letus Extreme if they are not available from Letus or their vendors. The Sigma f1.8 28mm has a 62mm filter mount.

The Nikon lenses become longer or shorter when focussed so the Letus front body mount pillar bridgepiece should be loosened on the rails and allowed to slide so the lens movement can happen.

The weight of the Letus Extreme should be supported and not allowed to hang on the relay lenses. The focus movements will otherwise become impossible to adjust.

The Nikon 35mm f1.4 may work as a direct relay on an unmodified Letus Extreme, depending upon how correctly centered in combination, both the camera sensor and the Letus Extreme optical paths happen to be.

I cannot capture from this camera. I will be sending the tape to another JVC owner who may or may not capture and post the footage.

The Nikon f1.4 28mm which has a 72mm diam 0.7mm pitch threaded filter mount with a Les Bosher Nikon-to-JVC adaptor mount will work turnkey from scratch as a relay with the Z1 adaptor ring on an accurately centered Letus Extreme which is also centered internally. As it is an internally focussed lens, the Letus Extreme body can be locked down to the rails.

A groundglass view, wider than motion picture frame is available. With the EX1 achromat, edge to edge focus on the groundglass appears to remain sharp.

The maximum aperture opening of f1.4 is not practically usable. Opening the iris ring that last click introduces a moderately severe "milky" artifact which seems to be some sort of interaction with the camcorder prism splitter as colour separation also occurs when the relay is defocused.

The Nikon f1.4 35mm also behaves the same.


"Normal" detail setting on the camera results in a similar artifact through the Letus on items like chain link fencing as is seen direct-to-camera. This occurs with both the f1.4 35mm as relay and the f1.4 28mm as relay. Detail probably needs to be wound back.

The f1.4 28mm is no longer made and its value is now more than the projected cost of the purposed direct relay lens which is in the works at Letus. Use of it as a relay would be pointlessly extravagant.

If a 62mm diameter filter mount adaptor ring could be made, the Sigma f1.8 28mm lens would be adequate stopgap direct relay if a groundglass view wider than the motion picture frame is required.

This arrangement in conjunction with Paolo Ciccone's Truecolor V3 scene file really looks magic in outdoors lighting. Greens especially are reproduced faithfully.


EDIT. Here is a web address to a very short SD extract from the JVC footage via DVD recorder. The vision is a bit soft and does not reflect the true image for sharpness at all. If you look closely in right half of frame, you may see one of our pestiferous bush flies come through the focus zone in the third shot.

http://exposureroom.com/members/DARANGULAFILM.aspx/assets/567354b362d84f7bba9fa25d62896f0f/

The HDV cannot be captured due to blown firewire port.

Here are some frame grabs also low res from a DVD recording of the JVC - Letus via Nikon direct relay test. They illustrate the comparative view of the groundglass for the same objective lens on front, which was a Nikon f.14 85mm.

The wider lenses may not work successfuly for relay unless the Extreme is accurately mounted and the internal optical path is re-centered. The 20mm begins to pick up an edge from the widened path on the one I have modified for about 2mm wider view of the groundglass.

FOOTNOTE: Sorry I think I broke the uploader. Will try again.

FURTHUR FOOTNOTE: Success. The black bar down the side is an artifact from forcing a recode of composite DVD-Video through AspectHD. The brown margin on left in the parrot feed shots is not an artifact, but the edge of a vertical window blind I had hidden the camera behind. I had hoped to grab a shot of birds fighting but they spotted the camera and shot through. The similar margin on the cricket practice frame was a metal fencepost I was doing pull-focus things with.

During playback of tests conducted today with the Nikon f1.4 28mm lens as relay, it was observed that in bright sunny high contrast outdoors conditions, a severe broad blue CA corona surrounds overblown white objects such as white vehicles and pinpoint highlights, a quite unacceptable artifact.

There is also blue-green blending in tree canopies.

Previous tests yesterday with the Nikon f1.4 35mm lens for relay were conducted in low-contrast overcast lighting conditions which would not have provoked this artifact.

This blue corona was also observed with the 35mm relay at night around headlights as previously mentioned so it is highly likely to occur with the 35mm lens as relay as well.

What a blow. However, this is likely the reason why the wait for a direct relay lens from Letus has been so long. The CA issue would have been waiting in ambush and may not have raised its ugly head until after some money was already spent on custom lenses.

The use of the Nikon lenses for relay of the Letus Extreme may be viable in controlled low contrast lighting conditions but for bright outdoors, especially in the 10am to 4pm zone they will come up short.

Sorry about the initial rush of enthusiasm but this is what R (without the "&D") is all about.

Be patient with the Le brothers and the other vendors on direct relay lenses for the JVC GY-HD*** , Canon XL** camera families and Sony Z7. It is obviously a tough nut to crack. It is certainly something you want to work right.

Thanks Bob for quickly adding this last post, I was already raising my hand with the scalpel and taking a deep breath before plunging the knife to severe the stock lens from its body when the computer went DING! -saying a theres a reply to the thread! -I held my hand, lowered the scalpel and read your post urging a stay in my cams execution... he got a timely reprieve.

My life is back to normal for the moment.

Furthur to the above posts I have fitted up the Sigma for Nikon f1.8 20mm. This has an 82mm filter thread and the 82mm ring for the JVC Fujinon lens will fit right in.

Just be careful as like the Fujinon and many camcorders, the lens filter thread and the body is plastic so you should avoid sideloading it. You will also find that the Les Bosher mount has to be taken from the camera and fitted up to the lens.

The bits and pieces inside the back of the 20mm come up firm against the inside of Les Bosher's mount and it is a snug and fiddly fit, more easily done with the mount off the camera.

On a HDTV, the very corners of the groundglass texture can be seen to be very slightly softer. The image area is very close to still-camera frame.

As previously mentioned, a non-modified Extreme may show an edge, probably the right and you may pick up the left as well.

When relaying with the 20mm, you get a wicked wide view with a 14mm f2.8 prime of the Nikon, Sigma or Tamron flavours. As the 14mm is a rectilinear lens, there is distinct corner stretch at this frame size.

Sharpness is adequate wide-open but it works better at f3.5. You will get brightness fall-off in the corners.

The Sigma f1.8 20mm lens flares wide-open and has to be at f2.8 before it goes away. This leaves little headroom to the f5.6 limit.

The 35mm and 28mm f1.4 lenses flare wide-open and should be regarded as adequate at f1.8 and better at f2.8.

The 20mm lens body is the longest of the lenses tested. Versus the standard Fujinon zoom, it saves you about 68mm in length and loses a bit of weight. The other lenses are shorter. The 35mm saves you about 91mm in length plus any distance stepdown rings may add if they do not all assemble to a common flush face.

Furthur to the above posts, Ted Ramasola has done some additional testing and finds that the stock Fujinon lens remains the best overall performer versus 35mm stills primes as substitutes.

The slight gain of a shorter combination does not outweigh the realities. Mass produced consumer 35mm stills lenses cannot be expected to yield a superior result to the professional purposed lens of the JVC, albeit also made in relatively high volumes.

So there it is.

The detachable lens style 3xCCC/CMOS cameras present unique challenges to lens makers, a known fact. Home hackers have hit a wall on this task, which requires the skills and R&D resources of optical engineers to solve.

Quyen, Hien, also Dennis, Wayne and Brian may be quietly observing this highly public exercise with wan sympathetic smiles on their faces. Perhaps they are having a quiet laugh into their coffee cups, a privelidge they have earned, reminded that they have been on the same difficult journey.

So my recommendation is to remain patient. Give them time to get their solution sorted.

They have to be able to offer something that outperforms and is more convenient than the standard lenses for these cameras, which means optical engineering of equal or better quality. That comes neither at mass-produced consumer prices nor at off the shelf convenience in the form of a product which can be re-purposed.

FOOTNOTE:

The TV program "Mythbusters" must be a fun thing to do.

Original post died on its bum so this is a quick recall of it.


Test of the Sigma for Nikon f1.8 20mm yields similar results as the other two lenses. The view is wider. Flare reduces the utility of this lens to f2.8 and no wider for relay.

Zebras must be used to keep overblown highlights in check.

The wide 14mm f2.8 lenses exhibit corner brightness fall-off and extreme corner stretching. The longer f1.8 and f1.4 lenses are fine.

Relay focus is harder to set via the viewfinder or LCD screen as the groundglass texture is scaled really fine.

Interiors shot to indoors lighting are killed by flare from any hotspot beams on floors or windows burning out.

With only about three f-stops of headroom, the utility of stills lenses for relay is to be questioned compared to the standard Fujinon which comes with the camera and is made for it. So as mentioned above the purposed relay lenses from the vendors should be patiently awaited.


FINAL FOOTNOTE TO THE JVC GY-HD100 EXERCISE.

I fitted the standard Fujinon back onto the camera and then offered up the Letus Extreme via the 82mm adaptor ring. It fitted up with no problem.

As previously mentions, this Extreme has the special EX1 achromatic dioptre installed. I found as have some others have reported previosuly, some difficulty in getting a good relay focus. I removed the EX1 dioptre from the Letus body and into the optical path, substituted a Century Optics 4+ 58mm filter mount achromatic dioptre with a 72mm ring on it.

I installed this to the Fujinon lens within the front of the plastic anti-reflection cone, the same hack as with my own AGUS35. The 72mm thread just bites enough into the shouders of the ribs to hold it. The rear flange face of the dioptre is exactly on line with the front edge of the rim of the rotating focus barrel of the Fujinon. Even closer to the front glass of the Fujinon might be even better but I did not experiment furthur.

I found that with the Fujinon focus set just under halfway between 1 and 1.2 metres and 37mm clearance between the flat face of the Letus rear body (not the rear edge of the achromat rim) and the front edge of the fixed shroud around the Fujinon lens (hood removed), workable sharp focus on the groundglass could be achieved.

With the re-centered and widened path in the modified Extreme, the zoom can be backed off to 20mm before the edge of the path comes in. With an unmodified Extreme with a fixed prism, I expect that the zoom may possibly still be able to be backed off to between 28mm and 35mm before an edge comes in depending upon the centering of the prism and the camcorder optics and their interaction.

Now all I need is an SI2K for about three days. I already have the hack together for that.

Here are some low quality grabs from JVC footage via SD DVD recorder - firewire port broken on JVC.

Frames are described as laid out :-

1 2
3 4
5 6
7

1 - 20mm relay of 35mm prime lens.

2 - 20mm relay of 14mm prime lens.

3 - 20mm relay of 85mm prime lens.

4 - 20mm relay of 85mm prime lens.

5 - 20mm relay of 28mm prime lens. Exposed for exterior natural lighting. (Table number stands are head positions for my intended actors.

6 - 20mm relay of 28mm prime lens. Exposed for interior. Note blue flare across window frames and overall smokey look.

7 - 28mm relay of 105mm prime lens. Note blue flare on car roof.


The location of frames 1 to 6 is The Elizabethan Village, 23 Cannes Road, Bedfordale, about 40 minutes drive south from Perth City, Western Australia. It is a precinct which replicates a tavern William Shakespeare apparently visited and Ann Hathaway's Cottage is replicated nearby.

For a pre-production promotional trailer, I hope to use the building as a representation of a tavern or tourist pub in the former Macedonia by adding a few artifacts and signage and restocking the bottle shelf with authentically labelled product.

If you happen to be in Perth and go out there for a good feed in the restaurant, tell the management I sent you but please be on your best behaviour.

Not far up the road was a replica of late prolific Mills and Boon novel writer Barbara Cartland's "Camfield". The landholding has now been cut up and developed as houseblocks. I don't know if the original residence is still available for public access.

The location for frame 7 is the Jull Street retail dragstrip in nearby Armadale, about 40 minutes south of Perth City in Western Australia.

No colour grading has been done in post. The images are ex camera via DVD recorder, converted in AspectHD, framegrabbed and converted in MSPaint to .jpg for upload. Camera was set up with Paolo Ciccone's Truecolor V3 with exception of detail being reset to "normal" for this test otherwise it was too hard for my weary eyes to see if things were in focus or not.

Here is a link to some vision of the 28mm and 20mm as relays :-

http://exposureroom.com/members/DARANGULAFILM.aspx/assets/be5d6c918fbd4028b3423893c6cc02d5/

In a few idle moments, I decided to try a published profile for the EX1 which can be found in the XDCAM EX forum here.

http://www.dvinfo.net/conf/sony-xdcam-ex-cinealta/110902-picture-profile-recipes-26.html


Below is a link to a very short clip of those shots. There are some stills in the sticky post in the XDCAM EX forum.

SONY PMW-EX1 - LETUS EXTREME TRUCOLOR V2 TRIAL By Bob Hart On ExposureRoom (http://exposureroom.com/members/DARANGULAFILM.aspx/assets/d46dec40cffd4f7d839d6b3f40a2cadd/)


There was also a piece of two-stop neutral density filter gel in the path between lens on front and the groundglass.

Here is a very quick and dirty test of the recentred and widened Letus Extreme on SI2K with Nikon f1.4 35mm lens for relay.

The grabs are .bmp converted to .jpg in MSPaint from 1920 x 1080 25P origination. There was a 2 f-stop lighting gel in the path I forgot about. - I wondered why I was not getting enough light. The gel was also cokeyed in the back of the mount so sharpness may have been degraded by this also.

Relay was on f5.6. Taking lens was on f2.

Garden was through a grubby thick glass window.

Test pattern is undersized in the frame which means the test which has actually derated the performance by about 15%. The "B" block at this reduced size still yields 862 lines.

The images have no look applied.

The limitations of stills lenses for relay to 2/3" are readily apparent. There is softening in the corners. A 28mm lens for relay just brings in edges of the Extreme's prism path on a 2/3" sensor.

It will be interesting to see what the Le brothers' direct relay for 2/3" can do in the SI2K when it comes out.

With an Extreme that has not been re-centred and widened, the 35mm lens for relay will just show a trace of one edge and pick up the other.

Here is a link to a furthur test of the Letus Extreme on SI2K.


SI2K - LETUS EXTREME TEST. By Bob Hart On ExposureRoom (http://exposureroom.com/members/DARANGULAFILM.aspx/assets/e69f5c04e6054217a341e7016e0ffb59/)


The lens used for relay was a Nikon f1.4 35mm. The field-of-view of this lens of the groundglass to the SI2K's 2/3" imager is comparable to the Sigma-for-Nikon 20mm f1.8 I used on the 1/3" JVC GY-HD100.

A 40mm focal length lens might be more realistic to use for relay to get inside the obvious hotspot in thse images. There will be a sharpness hit but edge to edge performance should be better.


Second Episode.


Here's another link to a 20 second clip, this time with a 40mm for relay :-

http://exposureroom.com/members/DARANGULAFILM.aspx/assets/5f90b2ac7a254731a2bf98e37cfdbb62/

The shots were under-exposed, especially the shot of the toddler in the outdoor garden dining area. This was almost black and had to be pulled up a long way in brightness and contrast to be visible. The pattern artifact in the left .jpg image was not evident in the motion vision.

The location is again the Elizabethan Village, Shakespeare's Tavern.

For sake of comparison, here is a link to an earlier test with a f1.2 58mm Noct-Nikkor for relay. The resolution return from the restricted groundglass area "seen" by the the camera is evident but there is no edge falloff.

This is not a valid comparison as the camera was set to 1280 x 720 25P. I think this means that a smaller area of the sensor image is recorded, therefore brightness falloff may have occurred in the areas of the sensor not recorded. Somebody with the knowledge might correct my comment here.

The camera operator in this instance knew what he was doing and did not underexpose the image and the lighting was indoors and controlled.

LETUS EXTREME TO SI2K CAMERA TEST. By Bob Hart On ExposureRoom (http://exposureroom.com/members/DARANGULAFILM.aspx/assets/b3f1c4d4461d4cd3a93df3782717e73f/)


FOOTNOTE: So as not to duplicate a post, there are a couple of frame grabs of test charts in the SI2K thread :-

http://www.dvinfo.net/conf/silicon-imaging-si-2k/127880-letus-extreme-si2k.html#post982123


FURTHUR FOOTNOTE: A very short clip from which the grabs came is here :-

http://exposureroom.com/members/DARANGULAFILM.aspx/assets/519a11dfd638414ea8703892218d491a/

Bob,

I received the raw footage tape you mailed to me and have managed to capture to my PC the tests you did.

I must say that the SD thumbs you posted don't do justice to the actual images i viewed on my CRT monitor.

Looking closely at the images, especially at the CA areas I looked back to my own tests way back and was thinking that perhaps it was caused by your achromatic diopters and not the relay lenses themselves.

I'm not sure what comparisons you made, but perhaps comparing different achromats on a setup that can intentionally induce CA, like using shiny metallic objects and high contrast colors, in a controlled set.

I'm continuing on my own tests using a different combination of macro and zoom settings on the stock fujinon to get optimum usable GG area. Pushing the macro to full makes me zoom in tighter. I will posts results later.

Ted

Ted.


Image quality of my clips aside one way or another, the JVCs may be getting a bit old but they still are a wonderful piece of gear to work with.

A rough instruction set can be found here :-

http://www.dvinfo.net/conf/silicon-imaging-si-2k/127880-letus-extreme-si2k.html#post983328

I was recently requested for some information on the mod I did to a Letus Extreme so here is the essence of the reply.

It is by no means the best or only method but simply a revisit of how I went about it. There may be other better and safer methods so owners who choose to modify their Letus Extremes should examine and enquire with qualified optical and machine engineers as to the best way to go.



INTRODUCTION.


As previously stated, the Letus Extreme at its pricepoint is quite satisfactory for aquiring 35mm motion picture size groundglass images into most camcorders it is designed to fit and should require no interference unles it has been damaged in shipping in which case it should be either returned for repair or an insurance claim made.

There are a few of us, who crave that last little bit of extra performance beyond a automotive designer's intent, forged rods and roller rockers, nitrous etc., etc.. Groundglass adaptors are no exception.

In the case of groundglass adaptor owners, such obsessions also exist. It is chasing that little bit extra "apparent" shaprness that can be had by scaling the texture (grains) of the groundglass smaller relative to the camera frame size by using a larger image area off the groundglass.

As previously stated, the risks and consequences associated with entering and making changes to the device are and remain the responsibility of the owner. Warranties and guarantees will become void.

Unless persons have good dextoral skills, basic engineering skills and access to machine shop equipment, this modification should not be attempted as the results may be disastrous.



Firstly, to get the prism central, you may simply get away with replacing the rubber wedge with a squashed piece of clear plastic tube like hospital UV drip tube cut long enough that it goes across the entire width of the prism instead of wedging one end.

You may need to add a bit of soft rubber or blue tack against one end of the prism to stop it from rattling as the plastic tube will not wedge it in all directions like the rubber wedge does.

If you are going to go ahead and do the full adjusmtent mod there are a few things to be aware of.


There are two distinct modifications I did.


Making the compound prism adjustable.

Widening the aperture of the condensor port.


Making the compound prism adjustable is relatively easy, requires good dextoral skills, a basic workshop, an accurate drill press, correct sized drillbits, small grubscrews and matching thread tap (cutter) of good quality silversteel. The discount ones are just not good enough.

Widening the aperture of the condenser port requires a good milling machine and skills to use it. The widened port does not add much more utility because the widest lens you can use will be a 20mm f1.8. Anything wider and anything tigher than f1.8 will vignette.

I did not keep my measurements so you will have to wing it.


You'll also need :-

Shim metal. Brass is okay, steel is better.

Very thin clear hard plastic sheet to wrap over centre spine. Shirt packet plastic should be fine. This is to avoid friction damage to prism surfaces as this becomes a moving bearing surface once you start using the adjustment.

A piece of nylon, or thick plastic to make the clamping piece which replaces the rubber wedge.

Contact adhesive (yellow toluene based glue)

Stick-on black felt material of about 1/16" or less thickness. Craft and hobby stores may have it.

Black parcel marker. You will have the prism out so you may as well blacken the ground areas on the sides and the centre support facet while you are at it. (There is a special carbon paint or dressing lens makers use which is best but probably impossible to aquire outside of the industry.)

Clean padded or cloth work surface lint free and changeable. Essential to avoid damaging gassware if you drop it.

Plenty of toilet tissue or facial tissues.

Several proper (usually purple coloured) microfibre lens cleaning cloths.

Solvent for dissolving grease.

Vernier caliper with depth gauge.

Machine vice for drilliing - desirable for accuracy in drilling the hole on the centre ( facet) corner of the case.

Cotton tips, cotton balls for cleaning.

Jeweller screwdriver set.

Allen key wrench set.

A sheet of thin cardboard or plastic to make the spacer gasket to go between the front of the case and the rear face of the front cover. This has to be twice the thickness of the felt layers you install inside the case.


GOTCHAS.

The inside of the prism enclosure case has been covered with grease to entrap any dust or loose machining particles which might have eluded the cleaning process in manufacture.

This stuff will get all over your fingers and transfer onto the prism faces unless you are exceptionally careful.

Cleaning it off the faces is a real bitch. Practice cleaning with a piece of window glass before you take this on. Until you can clean glass absolutely spotless, it is pointless opening your Letus because you are only going to ruin it and send yourself quite insane trying to get the glass immaculately clean. Anything less than perfectly clean is useless.

My routine for cleaning off grease is > solvent in tissue or cottonwool > Household detergent wash > Wash with simple bathroom soap > Clean water rinse. > Tissue dryoff and polish off with lens cloth. Fogging with breath for dampening to remove missed spots is fine but breathe gently. Microspots of spit are a mongrel to remove.

After cleaning and during re-assembly, soft cotton gloves are a good move to avoid fingerprints. Give them a wash before use to remove loose fibres.

After re-assembly you are going to find bits of dust and fibre everywhere. Use the cotton tips to pick off, don't rub as stuff in the cotton tips may come off.

The achromat is particularly vulnerable to being dropped as the Le brothers have used a UV cure or two-part clear cement to bond the glass elements into the metal rim.

The glass cracks away at the bond points. If it gets edge chips, this is not a showstopper. Use some black to limit the light the chips throw back into the image and maybe make a cardboard ring to mask off the chipped edge.

When fixing a loose achromat back into its rim, first remove completely all the bits of broken glass which will be sticking to the rim. Blacken the frosted side of the lens glass while you ared at it. Blacken any chips.

Use a few spots of water cleanup white bathroom sealer to secure the glass back into the rim. This stuff does not go totally hard and wile help protect the glass against future knocks.

The thin plastic you use to cover the centre spine should not result in a tight fit of the prism over it. The prsim should slip fairly freely. Any tighness needing forece to insert the prism will cause loading of the UV bonded joints in the prism and they may separate destructively.


METHOD.

Remove front tube.

Remove groundglass panel with motor attached.

Unsolder wiring from joint near edge of case. Do not unsolder from the motor end.

You will have to pick off the clear glue used to seal the soldered joint.

Remove battery compartment.

Remove rubber wedge.

With tissues or gloves worn, remove the compound prism by pressing through the achromat hole with finger as close to centre spine as you can get you finger to go.

Support the compound prism from the front with finger over the gap where the centre spine pases through the prism. Keep the prism as closely against the centre spine as you can while sliding it out to avoid contact with crease on the inside of the case.

Clean out all grease from within the case with solvent and tissues. Wipe out all bits of loose fibre and lint left behind. Don't bother to paint the inside black. It is okay as is.

Drill and tap the grubscrew holes.

Side hole on the facet corner is 27mm from rear exterior face of the case (camera side ).

The two end holes are 14mm in from the rounded facet corner more or less at the centre point of the circle of the rounded corner. Measure in 14mm with the tail of the vernier from the flat sides and the centre edge of the round to find the 14mm centre where the radii cross over.

Use a larger bit by hand to scarf out the swarf from the edges of the drill holes.

To tap the threads accurately you may find it easier to control the thread operation by mounting the thread tap in a Dremel tool chuck, mount the case in a vice and to hold the Dremel tool with one hand and rotate the chuck by fingers.

Important. - The grubscrews must have smooth almost flat, slightly rounded ends, not cupped or pointy ends. Cupped or pointy ends will cut through your metal shims and destroy the prism by chipping or cracking it.

Clean the swarf with a the larger drillbit as before.

Cut and glue on two layers of thin felt along the pivot lines front and back.

Cut and glue on single layers of thin felt along the edges of where the small prisms make corner contact on the front and rear faces of the case.

Cut and glue a single layer of felt about 16mm long in centre of the narrow edge of the centre spine directly opposite the screwhole which presses against the nylon strip. This piece of felt is equally important as a pivot point. The adjustment will not work without it. This piece is not evident in the video.

Cut and fit the thin plastic sleeve which fits over the centre spine. Fold it over the spine from the front. Make to holes for the screws to fit through. This stops the plastic from moving about too much. This plastic can be clear hard shirt packet plastic or plastic shim if you can find some.

The fit should be free not binding. Paper instead of plastic is sort of okay in a pinch but may swell in dampness and fret, leaving bits of loose fibre drifting around inside.

Cut your pieces of thin metal shim. These should be thinner than the two layers of felt otherwise the rpsim adjustment cannot work. Glue them down with contact cement along the inner edge of one side only. Leave the screw end corners free.

It is probably okay to glue them all the way across but the thickness of the glue at the corners may be hard to control and will take up space when it sets and make the adjusmtent process impossible.

Cut out your cardboard spacer gasket and fit it. I used two layers of cereal packet cardboard which is almost spot on 1mm thick.

Cut out your nylon pressure strip. Mark it into thirds lengthwise. File down the thickness of the end thirds about 1mm. This will leave the centre third as a raised area.

In centre of this raised area make a shallow hole for the end of the centre grub screw to bottom down in.

Cut it long enough that the centre hole will match the end of the grubscrew when the nylon strip is slipped in but not so long as it will jam tight when the front cover is fitted.

The nylon strip should be a tidy clearance fit between the prism and the case but not bind. You may have to file the side corners to match the slant of the curve in the case so that it is a tidy fit without being able to fall out of place inside.

It is absolutely important there is no direct contact by the end of the grubcrew against the centre facet of the prism otherwise it will surely be chipped or crack.

Re-install your prism. Check to see if it can rock on the felt pivots and no corners are clicking hard onto bare metal anywhere. Clicking is bad. It means a broken prism will happen in any hard knock.

Check your grubscrews can screw right through their holes. Make sure the ends are smooth and polish them so they do not cut through the shim metal.

Assemble the prism, spacer gasket and front cover.

Use your gloves to avoid staining the prism. Check again that the prism can rock on its felt pivots. If it can, put the grubscrews in and play with them.

Snug all up, then loosen the centre screw, loosen one end screw a counted number of quarter turns, tighten the other end screw up the same number of quarter turns to point of resistance only. Do not overtighten. If it works then dismantle everything, clean the prism, then re-aseemble and test.

To refit the pillars in their holes, pull the cups off, shove them into their holes with a blunt ended satay or chopstick filed down to a blunt end so that it can fit in centre of the cup not pushing on the sides. Push each pillar into the cups. You will feel a soft thud as they fit home.

If you want to adjust them forwards for initial backfocus, use tweezers to grab the pillars. Use a satay or roast stick as a lever with one end against the front cover of the prism case and the side of the stick against your tweezers and gently lever forward.

Use the vernier calipers to measure equal distance all around between the groundglass panel and front of prism case.

You should not need to bring the panel any furthur forward than 1mm at most.

So that you do not run out of adjustment, make sure all your faces between camera adaptor ring and rear of Letus are in contact with no gaps. Make sure the support rods and baseplate are adjusted so there is no bending load applied to the front of the camera.

There is enough compliance in the camera casework to allow the lens itself to move off-axis.

Enjoy, but please do not take this on unless you have the skills.

Prompted by Evangelos and his Thompson Viper - SGPro combination with a custom relay, I thought I would see just how much the Letus Extreme can be pushed. Bear in mind this specimen has been modified.

For a test on the SI2K, the relay lens was Nikon f1.4 50mm, with the Sony PMW-EX1, zoom just under 40mm was used. This is not a fair comparison between camera types. Exposures were not matched either. The EX1 achromat was used in both tests. I did try a forward offset of the Nikon lens with the achromat removed. I did not observe a resolution improvement which suggests to me that the groundglass resolution is the wall now, not the optics.

Here are two grabs. Letus 04 is with the SI2K. Letus 05 is with the EX1.

Resolution block "A" is 1920 horizontal lines of resolution, Block "F" is 1080 vertical lines of resoultion. A note on the back of the Lemac Chart states that the "A" and "F" blocks will not resolve on HD video. The moire patterns on both cameras suggest that sensors are seeing the lines on the groundglass which suggests that the Letus Extreme, when tweaked and given a dose of nitrous (not), can be made to resolve true HD, just.


Footnote:

When resetting the groundglass panel, my personal preference is to adjust to 19mm from front face of groundglass carrier to front face of prism enclosure, not the front face that the pillars are set into, but where the rear face of the tube butts against the prism enclosure. This is easier to measure with the depth tail of vernier calipers at all pillar attach points on the groundglass carrier.

Here is a link to a very short clip of a test with the Letus Extreme on SI2K camera.

LETUS EXTREME ON SI2K TEST By Bob Hart On ExposureRoom (http://exposureroom.com/members/DARANGULAFILM.aspx/assets/02457428f1d24a48ab6ba7f4ad44baa1/)

Because I got the whitebalance wrong, (forgot it altogether) I attempted a colour grade so it may not look all that flash as I am a little colour-blind. On the third shot, I forgot to turn the motor on.

Here is a link to a bit more testing. I have attempted to colour grade the images as the blue was a bit down and overall colour saturation was also down. There is static grain as I forgot to run the groundglass motor on most shots.

LETUS ON SI2K TEST By Bob Hart On ExposureRoom (http://exposureroom.com/members/DARANGULAFILM.aspx/assets/9576072fa72f4bfeb8f76b4c3854e676/)

The lenses used were Nikon 58mm f1.2 and Nikon 200mm f2, both at f2 - f2.8 with expsoure being controlled mainly at the relay lens which was a Nikon 50mm f1.4.

The lighting conditions were overcast, late winter afternoon so both relay and prime lens were nearly wide-open.

The Letus achromat being used is the one for the Sony PMW-EX1. It may not be correct for the simple prime lens I am using for relay.

(Yeah I know. - Backyard fruit trees are the bane of true orchardists as they tend to be neglected and thus harbour pests. These copped a strong wind a few days ago which dropped the oranges. I do put out bait traps for fruit fly.).

The EX1 achromat was designed because there was necessary some optical trickery to offset a problem specific to the EX1 zoom lens.

Excesssive video noise wil be observed in the citrus images. This is because I forgot to set blacks after shutting the camera down to save the battery.

After about a 45 year hiatus, I revisited a childhood haunt, the gully above the old orchard where I spent the first ten years of my life and went looking for the old pipehead my grandfather and father put in all those years ago.

This was in the days when the creek was permanent, people respected riparian rights and used pipeheads only to extract water.

Then the growers upstream put in huge dams, cleared the tii-tree swamps. the water stopped and that fixed us right up. The creek is now seasonal, dries up in summer, is flashy in winter.

The creek exacted its payback in 1991 when exceptional rains, cleared lands and urban street drainage sent a noahflood down which took out two bridges and rumour has it, one of the dams.

I found it almost unrecognisable, the bayonet grass has entirely disappeared, the course is all grown over with introduced bamboo, bridal creeper, watsonias and waitawhile vine - thorny blackberries, big alluvium builds through the bamboo and deep scours elsewhere.

I went up to have a look while the winter flow remains so that it was closer to my memories of it. Our one mile pipeline is still there but the pipehead and the first 50 metres of pipe is gone and the heavy bits and pieces are about 50 yards down the watercourse from when the flood and all the rocks and debris came down.

I shot with the EX1 and Extreme. I am too old and jointsore to take a big kit so made do with a light Miller DS10 and two lenses, 58mm f1.2 Nikon and 14mm f2.8 Sigma for Nikon.

Relay zoom position was 40mm. I gave the assembly an accidental clout on a rock as I scrambled about and knocked the centering off a fraction so there is an edge brightness falloff on the 14mm shots.

Conditions were late winter afternoon, clear overhead sky, deep canopy in deep gully.

A couple more frames from the creek.

Local wildflower related to bacon-and-egg-plant and remains of the pipehead washed down falls into the scourhole. About 50metres of the pipline was carried away and disappeared.

Being brittle cement pipe, it probably broke up into fragments among the debris going over the falls and may be well downstream by now in the bamboo thickets.

Sigma-for-Nikon f2.8 14mm was used on both frames.

Here are a couple of pics of the Letus Extreme-on-SI2K hack with the EX1 achromat.


I found I achieved much less edge brightness falloff when space was added between the front of the prime lens and the achromat. Best seems to be 79mm, measured from rear of flip enclosure on the Letus to front of IMS ring on the SI2K for the Nikon 45mm f2.8 lens used as relay. In this illustration the Nikon 50mm f1.4 is fitted.

There is a compromise between falloff and loss of corner sharpness when adding distance.

For relay, the 45mm Nikon seems to be the best. Voigtlander 40mm f2 and Nikon 50mm f1.4 exhibited a little more corner softness.

The shoulder on the brass ring is a bit short. It should butt against the rear of the flip enclosure. The material is expensive so I used what I had left over which was a bit short.

Sorry. Can't give you the worktitle for the present as it is not my project. Whilst the clip is publicly accessible, the information I am privy to is not yet. My recall is that this scene was a flashback. Warning for the sensitive and underage - this is a criminal "hit" scene with gunfire and spatter FX..

Subsequent footage for another scene was shot on a Canon 7D with the same and another similar Nikon lens kit.


Lens kit on the day from recollection :-

Nikon 14mm f2.8
Nikon 25mm f2.8
Nikon 50mm f1.4
Nikon 85mm f1.8
Nikon 105mm f1.8
Sigmatel-for-Nikon 135mm f1.8


Conditions on the day were hostile for adaptor use being intermittent light to medium bright overcast.


Junkyard Scene 1st Cut on Vimeo

I found this happy snap related to a fun action shoot from about two years ago on the facebook.

They are a bunch of young film-makers who are developing an action style and honing their skills and their stuff is looking pretty slick now.