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06-08-2013, 02:06 PM   #16
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QuoteOriginally posted by vonBaloney Quote
I have heard of a few incidents involving the K20D of the mirror just hitting the back of the lens.
This surprises me. The mirror boxes on the K20D and K10D are essentially the same. It also surprises me that there is any interference at all on an APS-C camera. After all, M42 Yashinons were originally fitted to full-frame 35mm SLRs with the same registration distance as Pentax dSLRs, but having mirrors that were 50% larger in each dimension.

As a check, a person can always simply do a side-by-side comparison of a K-mount lens and the suspect M42 lens. Line up the the lenses' back flanges (the part intended to contact the body mount flange) with each other and note how much the M42 lens's back element projects beyond that of the K-mount lens. I did this with my Auto Rikenon 55/1.4 which has a significant extension beyond the mount threads and was pleased to note that the actual depth was less than my FA 35/2.

Mind you, there may still be issues when used on Canon FF dSLRs, but that is a different story.

Edit: I did a little research and found that there are historic issues with the DX lenses on non-Yashica 35mm film cameras as well as a few reports of issues on K10D and K20D dSLRs. Why this should be is a mystery unless Yashica bodies at the time had an unusually shallow mirror and/or a sophisticated swing mechanism to help the mirror clear deeper lenses. Again, I would suggest visual comparison with lenses that are known to not cause problems before attempting to mount.

Edit 2: Extensive thread on this site regarding the DX lenses, mirror clearance and such...includes measurements:

https://www.pentaxforums.com/forums/pentax-slr-lens-discussion/160235-yashica...ge-mirror.html

I feel particularly dumb at this point since I took part in that and another earlier related thread.

Steve


Last edited by stevebrot; 06-08-2013 at 02:59 PM.
06-08-2013, 02:38 PM   #17
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QuoteOriginally posted by Rense Quote
I searched the forum for examples of M42 Yashinon lenses but they seem to be in disgrace.... Not that there are no examples, but in comparison to other legacy lenses, Yashinons seem to be very underrated. Any idea why?

I only have one Yashinon, but I like it a lot. It's the Auto Yashinon-DX 50mm F1.7, and it delivers great photos, both normal, as well as mounted on a 25mm extension tube...
Here is some information on Yashica lenses

Last edited by interested_observer; 06-08-2013 at 02:55 PM.
06-08-2013, 02:38 PM   #18
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QuoteOriginally posted by stevebrot Quote
This surprises me. The mirror boxes on the K20D and K10D are essentially the same. It also surprises me that there is any interference at all on an APS-C camera. After all, M42 Yashinons were originally fitted to full-frame 35mm SLRs with the same registration distance as Pentax dSLRs, but having mirrors that were 50% larger in each dimension.

As a check, a person can always simply do a side-by-side comparison of a K-mount lens and the suspect M42 lens. Line up the the lenses' back flanges (the part intended to contact the body mount flange) with each other and note how much the M42 lens's back element projects beyond that of the K-mount lens. I did this with my Auto Rikenon 55/1.4 which has a significant extension beyond the mount threads and was pleased to note that the actual depth was less than my FA 35/2.

Mind you, there may still be issues when used on Canon FF dSLRs, but that is a different story.

Edit: I did a little research and found that there are historic issues with the DX lenses on non-Yashica 35mm film cameras as well as a few reports of issues on K10D and K20D dSLRs. Why this should be is a mystery unless Yashica bodies at the time had an unusually shallow mirror and/or a sophisticated swing mechanism to help the mirror clear deeper lenses. Again, I would suggest visual comparison with lenses that are known to not cause problems before attempting to mount.

Steve
Yashica's own later bodies came with warnings not to use DX lenses...
06-08-2013, 03:18 PM   #19
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QuoteOriginally posted by vonBaloney Quote
Yashica's own later bodies came with warnings not to use DX lenses...
Yes, I found that quote from a Yashica manual. The warning specifically indicated that there had been a change in mirror design that caused the incompatibility. I also found that the the DX lenses had a long run with several different variants in terms of build. That may account for some users having no problems. It seems that the clearance issue is very slight. One Pentax user was able to use emery paper to remove a slight amount of material from the metal shroud on the rear element to create clearance for the mirror.


Steve

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