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08-18-2011, 02:18 PM   #16
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QuoteOriginally posted by newarts Quote
I countersunk the holes I drilled with a drill bit; using a punch I'd worry about deformation beneath the ring causing it to seat too high - has this not been a problem in your experience? If not that's nice to know.

Russel's adapters are chrome* plated brass. He delivers fast.

* uhh maybe nickle plated? shiny at least!
It depends on the lens. Typically the original mount is thicker than the m42 adapter. If the original mount was .060" and your adapter is .040", you loose .5mm which is exactly how much you want to loose to change an olympus lens to pentax (actually .44mm to be precise). If the original mount was thicker than .060", you are going to have to use a spacer to push the mount back out. I converted an f.zuiko 50mm 1.8 and the dents sticking out where I bent the counter sink provided nearly the exact amount of shimming I needed (I files just a hair off the nubs to fine tune the focus). I converted a vivitar olympus mount and the original mount was about .270" thick! I used a .200" thick step ring as a spacer and a mount stolen off another lens that was about .070mm. It focuses just past infinity. I could just thin down the step ring a little (about .020" taken off I guess) If I really wanted it perfect.

08-18-2011, 03:06 PM   #17
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QuoteOriginally posted by ripit Quote
It depends on the lens. Typically the original mount is thicker than the m42 adapter. If the original mount was .060" and your adapter is .040", you loose .5mm which is exactly how much you want to loose to change an olympus lens to pentax (actually .44mm to be precise). If the original mount was thicker than .060", you are going to have to use a spacer to push the mount back out. I converted an f.zuiko 50mm 1.8 and the dents sticking out where I bent the counter sink provided nearly the exact amount of shimming I needed (I files just a hair off the nubs to fine tune the focus). I converted a vivitar olympus mount and the original mount was about .270" thick! I used a .200" thick step ring as a spacer and a mount stolen off another lens that was about .070mm. It focuses just past infinity. I could just thin down the step ring a little (about .020" taken off I guess) If I really wanted it perfect.
I think I need to learn how to adjust a lens for focus at infinity. It must be adjustable and not too hard to do; manufacturing tolerances aren't good enough to avoid it as one of the last assembly steps.
08-18-2011, 03:21 PM   #18
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Actually, looking back I did file it down to fine tune it on the one I bent the countersink into.
pics are in post 8 and 9
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/144255-lens-no...12-oclock.html

I think I'm getting confused between threads as the topic is similar in this thread
https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/135398-how-do-...k-mount-2.html

as far as fine tuning infinity, its going to be different on different lenses. Some are easy, some are not. As far as manufacturing tolerances being good enough to avoid major adjustment, as I understand it, with some old lenses, yes they are that precision made. Also as I understand it, many new lenses are designed and set to focus past infinity because the are no longer made that precisely. I have seen lenses where you loosen a screw under the grip and turn a collar to adjust. I have seen another where you loosen a few set screws and turn the front group of glass to screw it in or out a little.
08-18-2011, 03:40 PM   #19
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QuoteOriginally posted by ripit Quote
Also as I understand it, many new lenses are designed and set to focus past infinity because the are no longer made that precisely.
I've certainly seen people post here saying new lenses focus past infinity because they aren't made with the same precision, but this person contends it's useful to focus past infinity at visible wavelengths so that you can focus to infinity at other wavelengths, implying it could be intentional:

QuoteQuote:
"I have been contacted by one astronomer that inquired about the possibility to focus at infini with a Canon sensor on a camera deprived from its IR filter. The consequence of removing this IR filter is a change of the back focus distance of about 0.8 mm: it's as if the lens was moved away by 0.8 mm from the camera mount. As some lenses have been designed with the infinity mark on the focusing distance on the scale having a small extra angle of turn beyond infinity before being stopped to cope with this situation, we decided to make a test and see if the Samyang lens could still get a crisp image when set to infinity and when the lens is temporarily mounted with a 0.8 mm gap between the camera and the back of the lens mount: the result was unambiguously negative. The whole image is badly blurred @f/3.5. An optical corrected adaptor must then be used to make the Samyang fisheye suitable to a camera from which the IR filter has been removed."


08-18-2011, 05:58 PM   #20
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QuoteOriginally posted by nater Quote
I've certainly seen people post here saying new lenses focus past infinity because they aren't made with the same precision, but this person contends it's useful to focus past infinity at visible wavelengths so that you can focus to infinity at other wavelengths, implying it could be intentional:
It's probably either or both depending on the lens (some lenses have focus marks for IR focus). Another one I have heard is that it allows for variation in temperature implying shrinking and contraction of parts (in particular with new lenses that mix a lot of metal and plastic I would think). All 3 are probably true to some respect.

Regardless, my point was its not that important to fine tune it exactly as long as it goes past infinity (maybe far enough past infinity if you take these issues into account). If its too short you loose infinity focus which is an issue. I wouldn't think loosing a little of your macro range would not be as big a deal. Thats my feelimgs about it anyway.
I'm certainly no expert but my limited experience tearing apart lenses (just a handfull recently but a few all the way and back together working) tells me it varies quite a bit how easily and how much you can fine tune focus and it varies how it is done. This is based on tearing lenses completely down not just changing a mount.
08-18-2011, 07:24 PM   #21
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QuoteOriginally posted by ripit Quote
When you say you glue an extension section around the lens body, do you remove the aperture ring and just glue the mount with a ring to the lens?
I haven't had to remove any aperture rings yet. Depending on the lens (NOT Nikon mount!) the body may extend far enough beyond the aperture ring for the extension section to have a good grasp. And I'll admit that this is a trick I use mostly on projection lenses, although I've done this with a Retina-C lens also. This is just a general trick for providing a cheap mount for lenses within certain size ranges.
08-18-2011, 07:41 PM   #22
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Seems like its a little different with every lens. I'll keep that in mind should I attempt any lenses where it looks like that would work.
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