Instruction Set for fitting up SI2K and Letus EXtreme
 

A rough instruction set can be found here :-

http://www.dvinfo.net/conf/silicon-i...tml#post983328

Roiding the extreme - a few hints
 

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.

GM -v- FORD sort of
 

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.

Short Clip of Letus on SI2K
 

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

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.

Furthur try-out of Letus Extreme on SI2K
 

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

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.

Some grabs from a bit of a hike today
 

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.

Short film in production.
 

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.

Budget Film-making West Aussie style
 

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.

Re: Roiding The Extreme
 

Here's a bit of EX1/Letus Extreme footage I shot for a family history project and began to put together untl the editing computer gave up. It is the vision the stills furthur back in this page were extracted from.

STONY GULLY RETRO PT.1. - YouTube

Re: Roiding The Extreme
 

To enable someone to have an idea of how some old Taylor, Taylor and Hobson Speed Panchro Series II lenses looked, the only tools I had were the EX1 and Letus Extreme, so I hooked them onto that and shot a test card. the lenses were 50mm and 75mm.

These are early 1950s lenses and damaged ones at that due to fungus from tropical storage. Despite that, they are still not bad but flary, the 75mm more so due to front surface scratches from cleaning. They throw images with no soft corners and the lines are straight. The lenses are physically small compared to stills primes but throw a wide image. The frame grabs are not the best. They are a bit pixellated.