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Old August 24th, 2007, 08:31 PM   #1
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Adaptor Problems (LetusXL)

Here are the images:

As you'll see from the images, the main chasse is building a seam. When I put my heavy 55mm 1.2 lens on it, the seam gets larger.

The second issue is when I mount the lens on the metal adaptor; it has a problem with back focus. I have to adjust the metal mount to tilt forward to get acceptable focus.

Any suggestions?


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Old August 25th, 2007, 06:16 AM   #2
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Have a look at the Clayton's sticky on the Letus above. There are links to Youtube vision where a XL model is stripped down. You will see in the early part of the clip, one partial solution to the backfocus problem and the unsteadiness which occurs when you move that mount ring forward.

For the Canon lenses, I don't know how much shimming has to go in behind the mount.

The "crack forming" is a Letus flip trait. Some units relied entirely on adhesive bonds between the tube sections and flip enclosure shoulders which fail.

I see there is a screw there. You may have to drill and tap a few more as the screwhole itself will be stretching and may eventually tear through the shoulder material.

The only permanent solution will be for Quyen to remake the design of the flip enclosure with deeper shoulders, especially the rear one which holds the relay tube. There may be practical design reasons why this cannot be done like billets of machinable ABS being available only in certain sizes or suchlike.

In meantime, I find that yellow toluene based contact adhesive works fine on the joints which are meant to be permanent, perhaps too well because subsequent dismantlement is almost impossible. The screws are removed and the joint separated, a thin line of glue applied to the shoulder outer and tube inner circumferences and the join restored. You scratch matchmarks across the joint before you part it so you don't put it together wrong. If you don't feel confident to do this repair, I suggest you contact Quyen.

Don't use adhesive on the front end piece which carries the lens mount and fits in the frontend of the front tube . This is meant to be removable.

The downside to using this stuff is that strings come off it across lenses and mirrors if you are not careful.

In short, that joint needs attention rather urgently. If you dont have the skills or hardware to drill and tap more screwholes, the yellow glue should be adequate. Allow a half-millimetre fillet of glue to remain in the corners of your joint.

Dont clean it off. If it looks zit-yellow ugly which it likely will, use a black felt tipped marker to cover it over after it has set and dried for a few days.

If your budget can extend to a Cavision rod and baseplate set, they also make a little hammock-strap thing which fits under the Letus body and supports it, taking the weight off the Cannon mount and the modified Minolta SLR lens Quyen uses for his relay lens, all good and makes the relay backfocus a lot easier.

Last edited by Bob Hart; August 25th, 2007 at 06:37 AM. Reason: error
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