Roiding The Extreme

[Bob Hart]

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.

[Bob Hart]

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/DARA...b07bb39e69a48/

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.

[Dennis Murphy]

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

Cheers.

[Bob Hart]

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.

[Dennis Murphy]

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

[Bob Hart]

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.

[Bob Hart]

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

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/DARA...a4ac4a5830b07/


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.

[Igor Babic]

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.

[Bob Hart]

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.

[Igor Babic]

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.

[Bob Hart]

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.

[Bob Hart]

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

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.

[Bob Hart]

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.

[Bob Hart]

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.

[Bob Hart]

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.