Looking for Letus Extreme 72mm Thread Ring & Achromat at DVinfo.net
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Old April 8th, 2010, 05:34 PM   #1
Regular Crew
Join Date: Nov 2008
Location: Holmdel, NJ
Posts: 81
Looking for Letus Extreme 72mm Thread Ring & Achromat

Well, I successfully cracked my letus extreme's achromat and stripped the threads of the ring.
I'm looking to see if anyone is willing to sell their 72mm Thread Ring & Achromat, maybe if they dont need it after purchasing an optimization kit.

I own a 82mm Thread Ring and a 82mm Thread Ring Cap (worth $125) that I'd be willing to trade.

PM me with your offer or email me at kevinsaw@gmail.com.
Paypal only.


Standard Achromat- http://www.letus35.com/cart/images/P/achro-prod.jpg
72mm Thread Ring- http://www.mitcorp.com/public/produc..._t-ring-77.jpg
Check out my blog at KevinSawicki.com
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Old April 8th, 2010, 11:28 PM   #2
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Join Date: Dec 2003
Posts: 4,475

I can well imagine your disappointment. However all may not be as lost as it first seems depending on the damage.

Just how broken is the existing achromat?

If it is just edge chips and they are no more than about 5mm across towards centre, you might just get away with re-using the glass element with the edge chips heavily blacked out with several layers of felt tip marker ink or thinned blackboard paint.

Wash the glass element throughly first by submerging it in water. Polish the edge chips with a soft sponge whilst holding the glass under water. Hopefully any tiny flakes of glass will come off, sink to the bottom and not remain to do any scratch damage later on. Do not use the sponge for lens cleaning again as there may be some glass flakes in it.

Scrape out and clean away thoroughly, the chips and fragments of glass which remain in the metal rim. Do this underwater to avoid any bits coming off into your eyes. Optical glass is a bitch for any opthalmic surgeon to search for and find. Do not use air or blow out loose stuff with your mouth for the same reason.

Any sponge, dishcloth or cottonwool pad or ball you use to clean the rim, do not re-use on the lens later. Use a new one to avoid scratches from loose glass fragments.

The glass element should be positioned so that the chip is masked by the upper or lower frame of the rectangular rear port. Blacking out the frosted finish around the rim of the glass element won't hurt either because any new adhesive you use there may reflect flares back across the lens.

To refix the loose achromat into the screw-out rim, first make up a paper or thin cardboard mask to cover the back of the prism in the Letus case from getting adhesive on it.

Chances are, there will be a few tiny crumbs or flakes of glass loose in back of the Letus or on the rear surface of the prism. Use a damp cotton tip to pick them off. Don't wipe them off the glass because you will scratch it. Don't blow them out for the same eyesafety reasons mentioned above. Droplets of your last dinner might also end up on the rear face of the prism and that sometimes takes some cleaning because of oil content.

Screw the achromat rim into the back of the Letus to its firm position. Don't overtighten. This is so that you can correctly orientate the chip in the glass.

Lay a thin cover of water-cleanup bathroom sealer in three spots around the inner surface of the rim. Do not use the vinegar smelling silicon type as it is impossible to clean off glass.

Lay a thin cover of water-cleanup bathroom sealer in three spots around the outer frosted surface of the glass element.

Turn the Letus body on its back with the rear facing down. Make sure the chip is positioned to hide behind the upper or lower frame edge of the prism port. Gently shove the glass element up into the rim until it is fully home, the turn the Letus face-down to keep the achromat in there.

This may seem fiddley and awkard but it is done this way to avoid the glass element from dropping into the hole with a thud, or jamming crooked and doing more damage. It also helps to avoid smearing adhesive or crud on the front surface.

Make sure you put the achromat in facing the correct direction. The chips crunched out of the inner or front face of the element should tell you which way it should go back in.

After the sealer has set, unscrew the achromat out and remove your paper or cardboard shield. If it has stuck to the achromat, no problem. Just use a thin scalpel blade to trim it off.

Clean up the glass with dishwash detergent first, then new bathroom soap cake soap then rinse off with clean water. Don't do this too soon otherwise the water may dissolve the sealer and your glass may drop out of the rim again.

Polish off with a clean lens cloth. Start in centre and work your way out to the edge. Do not rub with heavy pressure otherwise any tiny flakes of glass at the edges of the chips might come off and scratch the surface.

That is one of the reasons for using the felt tip marker or thinned blackboard paint to immobilise any remaining flakes about to come off.

If by mistake. the position of the chip ends up on the side rather than top or bottom, do not overtighten to get it in the right spot. Instead cut thin paper washers to place under the face of the achromat rim to shim it out furthur until the screwed firm position puts the chip in front of the top or bottom frame edge.

Regarding stripping the thread on the ring. Is this the 0.7mm filter thread on the ring or the three setscrew holes around the edge?

If it is the filter thread not gripping in the front of the camera, I suggest you look at the filter thread in the camera itself. This is more likely to have been torn away by overtightening or crossthreading and a replacement ring is not likely to fix this problem. Many cameras have a plastic thread in there, not metal.

If the three setscrews have stripped, this also suggests overtightening has happened. A camera repair shop, or precision machinist may be able to drill out and tap larger screwholes in there, drill out and tap three new ones or drill out and helicoil the original holes. It might be cheaper to buy the new ring but there are options if you cannot.

If you are not using a rods/rails system for supporting the camera and Letus, I strongly recommmend you buy one. As well as protecting the lens filter thread in the camera body, it keeps the whole assembly rigid and everything stays centred once you have set it up.

Maybe post images of the damaged items and this will enable us to assess whether you need to repair or replace.

Last edited by Bob Hart; April 8th, 2010 at 11:41 PM. Reason: errors
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