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Old September 14th, 2010, 12:01 PM   #1
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Secondhand Letus Extreme - loose glass in achromat

I ran the eBay gauntlet for a Letus Extreme, which arrived today. All seemed fine, until I noticed a tiny shard (about 4mm long and 1mm thick) of glass was actually loose in the achromat... I can also see where it's chipped off from inside the rim. From what I've seen from videos of using the Letus, you zoom a fair bit in to the ground glass, so this shouldn't really be a problem as the little shard falls to the bottom of the achromat (and usually lodges itself stuck between glass + fitting). It definitely won't be "in shot".

Is this common with achromats? Is this is a bad sign that it could get worse, with further shards coming off? Or should I be fine, as long as I can keep it out of view?? I can take a photo if people want to see it!
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Old September 14th, 2010, 12:35 PM   #2
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My guess is that your Letus took a bit of a thump in shipping.

Rather than using a screwed ring inside the metal rim enclosing the glass element, which carries its own risk of crush or chip damage, the Le brothers decided to bond the glass to the metal rim. I do not know what adhesive they used but it appears to be a hard setting cement, possibly UV cured.

My personal preference would be to screw out the achromat from the case and remove that little flake of glass. You will need a lens spanner to loosen it by the two small slots milled into the rim. As light as it may be, you still do not want that loose chip abrading the rear face of the compound prism.

Another reason to take oput the achromat is that the chip is an indication that the glass element may have begun to detach from the metal rim into which it is bonded. Another bigger chip may not be too far away from happening if you bump or knock the adaptor during use.

Do "NOT" use the "chisel" method of trying to knock the achromat rim around with a screwdriver and an improvised mallet of some sort. If there is any doubt the glass is damaged beforehand, there will be no doubt afterwards. Optical glass is very fragile and you will likely damage it by this method, especially if it has already become partially detached. You also run the risk of chipping the compound prism by shock loading the case.

If you do not have a lens spanner, you will need to make up a simple blade spanner to to the job or take the appliance to a camera repair shop to loosen the achromat for you.

My personal preference would also be to want to resecure that glass element in the rim using a non-hardening water cleanable bathroom sealer.

Screwing out the achromat from the rear may carry its own risks. Another chip may occur as the metal ring is screwed out.

If the glass element is already loose inside the ring, then it needs to be resecured. If you do this, you also need to use a black felt tipped parcel marker pen or lens black and black out the chip so it doesn't flare.

If the glass element appears to be secure in the rim, then it might be better to leave it be and run a very thin bead of bathroom sealer around the edge of the glass in-situ to immobilise it against furthur movement.

While you are about it, if you have removed the glass element from the rim, you may as well black all the outer circumference of the glass where it has a frosted finish.

All the crunched bits of glass you find still glued to the metal rim have to be cleaned off before you put the glass element back in with bathroom sealer. Don't use the silicone based sealer as this is practically impossible to clean off from the glass. The wrong sealer can be identified by a vinegar or strong acidic smell.

When unscrewing the achromat, make sure the Letus body is front-downwards. When taking the achromat out of the body after uncrewing it, make sure you keep it facing down the same way as it comes out of the body. If you turn it over, the glass may have become loose in the rim, fall out onto the floor and be ruined.

Before you reset the glass into the rim, screw the rim fully home into the body, then note where the chip is and make sure the chip is either top of frame of bottom of frame in the area where the rectangular port will conceal it. Matchmark the rim and the glass with a felt tipped marker pen so that when you unscrew the rim to put the glass in, the chip will be in the right place to be hidden when you screw the rim with glass re-mounted, back into the body.

Do not overtighten the achromat into the rear of the body. Use a few very small dobs of sealer across the head of the joint to stop it from coming undone but not too big or the adaptor ring will not fit over.

Last edited by Bob Hart; September 14th, 2010 at 01:01 PM. Reason: errors
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Old September 14th, 2010, 04:00 PM   #3
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Woah thanks Bob... plenty to consider! I was under the impression that the shard of glass would be actually inside the achromat (and so unreachable), but it sounds like you think it's simply in between the achromat and the prism. I'll remove the achromat and see if it's as simple as that... fingers crossed. I'll also see if I can felt-tip the damaged areas. I'll let you know how I get on :)
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Old September 14th, 2010, 11:57 PM   #4
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You are welcome. What is it they say in America ? - "We aims to please".

What camcorder are you intending to use your adaptor on ? There were different achromats for different camera types. A particular one which cannot be substituted with satisfaction is the EX1/EX3 special achromat, which dealt with some special issues the Fujinon lens caused.

The EX1/EX3 achromat however seems to work fine with the Sony Z1/FX1 family.

If you also bought a rods system, use it. There is a lot of mass for the fragile lens filter threads on front of your camera to support. With many cameras, this 0.7mm pitch thread is cast in the plastic body of the camera and may strip with time and use. Your next move should be to buy a rods/rails kit.

To help avoid crossthreading when fitting the threaded ring into the camera, offer the ring up to the thead squarely, then slowly turn it anti-clockwise until you feel the little click as the start of the threads pass each other, then gently screw the ring clockwise into place. It is initially easier to point the camera directly up to the ceiling, then offer the ring downwards onto the thread when fitting up.

The threads in the plastic are cast, not cut on some cameras, so there may be some intial resistance until the thread surfaces dress with use. That resistance should be constant, not like the tightening resistance of a crossed thread.

Last edited by Bob Hart; September 15th, 2010 at 12:00 AM. Reason: added text
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Old September 15th, 2010, 03:04 AM   #5
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Furthur to above post, here's a link to a look inside for curiosity sake only. I do not recommend you go on this adventure. There is irrepairable damage which can be done.

ROIDING THE EXTREME. - ADDED LATERAL CENTERING ADJUSTMENT. By Bob Hart On ExposureRoom
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Old September 16th, 2010, 05:15 AM   #6
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Bob, you're a man very knowledgable in these parts!! How much do you think a second hand Letus B4 Compact Relay is worth? I have one that looks in excellent condition, but have no use for it. Pondering whether to hold for the future or sell on. It's one of these:

Creative Video Letus35 LTB4S Compact B4 relay (F1.8) - Allows direct fitment of Extreme / Elite / Ultimate to B4 mount cameras
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Old September 17th, 2010, 08:32 AM   #7
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I try not to get involved in valuations as it is so easy to get it wrong, for people to be disappointed and for market players to be harmed by anything I say which might turn out to be incorrect.

This would be one of those supply and demand questions. I looked up the compact 2/3" relay on the adapterplace and letusdirect websites and could not find it listed with a current price so it may have been discontinued. There were two 2/3" relays by Letus, the professional and the compact.

The value of anything associated with 35mm groundglass adaptors could be affected by the Canon 5D and 7D.

Yet, people who have B4-mount cameras might also be looking to use the adaptors direct to their camera if the price comes down to become more cost-effective with the Canons and extend the usefulness of their cameras. In that event, the demand for new and used B4 relay lenses might be preserved.

The intial novelty of the Canon cameras appears to have passed in that some 35mm adaptor owners have returned to using their adaptors and more industry-friendly cameras they already own.

So it is a bit of a gamble. Do you quit the B4 relay lens whilst it retains value. Aside from its purpose as a relay lens, I suspect it may also function quite usefully as a close-up lens but if you do not have a B4-mount camera then it is not useful in this way to you either.
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Old September 22nd, 2010, 04:25 AM   #8
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Just a quick update on the loose glass issue, I removed the achromat fine and the loose shard(s) of glass were accessible and came out easily - sorted!
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Old September 22nd, 2010, 07:40 AM   #9
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( In jest ). Don't you feel a whole lot better now ?

Time to hook it all together and shoot a whole lot of useless stuff to get the feel of it. - Enjoy.
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