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04-14-2019, 08:06 AM   #1
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converting M lens to A lens

can you take the aperture ring components from a 'A' lens and place them on a 'M' lens to make it an 'A' lens?

have the rear parts of a sears 135 marco 'A' that is rather dismantled but have a sears 135 (I will call it 'M' as no 'A' on the aperture ring...….will 'swapping' thus make a frankenstien 'A' by changing out the parts?

edit~ sorry failed to mention this but the idea is to obtain flash capabilities

thanks


Last edited by Aaron28; 04-14-2019 at 08:46 AM.
04-14-2019, 08:31 AM   #2
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QuoteOriginally posted by Aaron28 Quote
can you take the aperture ring components from a 'A' lens and place them on a 'M' lens to make it an 'A' lens?
You can give it a set of contacts, but the mechanical parts of the iris diaphragm may not be the same between the two lenses, even assuming the same maker. The actuator mechanism on non-A lenses is not designed and/or calibrated to provide a particular opening for a given motion of the actuator lever.


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04-14-2019, 08:38 AM - 1 Like   #3
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This has been done there is a thread or two here (somewhere...). The basic technique is to take the mount off and create a contact that activates the middle contact on the camera mount (see mount pics eg here). It can work but there is a fundamental difficulty: the aperture function is designed differently between M and A lenses. IIRC the ris moves linearly with the movement of the aperture lever on M lenses, but relative to the area of the iris on A lenses. So the exposure won't be consistent as you change f stop on a converted lens. However you could argue this isn't such a big deal as the main object would be for the exposure to auto adjust on the fly with changing light, and exposure isn't consistent anyway as f-stop is changed with many lenses (I am thinking esp of adaptall lenses with PKA mount).
More fundamentally, why don't you use the time and effort to simply get good with M mode... chimp and exposure bracket a lot...
04-14-2019, 08:39 AM   #4
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QuoteOriginally posted by stevebrot Quote
The actuator mechanism on non-A lenses is not designed and/or calibrated to provide a particular opening for a given motion of the actuator lever.
thank you Steve

04-14-2019, 08:44 AM   #5
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No idea but sounds like a fun project. I guess it all depends on the similarity of the two lenses. Certainly couldn't hurt to try,
especially with cheap, old, off brand glass.

You'll need to add everything "A" specific to the "M" lens, including the "A" style aperture ring, linkage(?) and bayonet with "A" contact.

Also, beware that Ricoh pin.
04-14-2019, 08:44 AM   #6
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QuoteOriginally posted by marcusBMG Quote
However you could argue this isn't such a big deal as the main object would be for the exposure to auto adjust on the fly with changing light
thank you Marcus

seems as it could work......its more about obtaining flash capabilities which I failed to mention in the first place
04-14-2019, 08:45 AM   #7
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M series, opening diameter changes linearly as it closes. A series, opening diameter AREA changes linearly as it closes.
04-14-2019, 08:46 AM   #8
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Get to it and let us know how you get on! 👍

04-14-2019, 08:49 AM   #9
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QuoteOriginally posted by tvdtvdtvd Quote
No idea but sounds like a fun project. I guess it all depends on the similarity of the two lenses. Certainly couldn't hurt to try,
especially with cheap, old, off brand glass.

You'll need to add everything "A" specific to the "M" lens, including the "A" style aperture ring, linkage(?) and bayonet with "A" contact.

Also, beware that Ricoh pin.
thanks! believe I have all the pieces as it was my favorite lens to use until it decided to pop in half! the ricoh already removed

did not consider the bayonet but I believe that's part of the 'A' ring....

---------- Post added 04-14-19 at 10:50 AM ----------

QuoteOriginally posted by marcusBMG Quote
Get to it and let us know how you get on! 👍
hahaha! thanks!
04-14-2019, 08:59 AM   #10
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QuoteOriginally posted by Aaron28 Quote
hahaha! thanks!
Watching for your reply to this thread with interest... as I have "Retro Lady" (SMC Pentax-M 40mm F2.8) that would no doubt love to be updated in her Harem status, to be the same as her Sisters.

I think that my "HM The Queen" (SMC Pentax 500mm F4.5) is too old to care about such things and is neither up or down about it all.
04-14-2019, 01:14 PM - 2 Likes   #11
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I did modifications of Pentax-M 50/1,7 and Revuenon 55/1.2 from non-A to A design. I like shoot wide open or up to f2,8 ar similar. So, I did not noticed huge exposure problems after modification.

04-14-2019, 02:19 PM   #12
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QuoteOriginally posted by Medex Quote
I did modifications of Pentax-M 50/1,7 and Revuenon 55/1.2 from non-A to A design. I like shoot wide open or up to f2,8 ar similar. So, I did not noticed huge exposure problems after modification.
sweet! that's awesome
04-14-2019, 07:40 PM   #13
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I'm going to follow this thread too. I have a M 135mm Sears lens and the Macro Sears 135mm A that is debuncted, fungus filled. Woulld be nice if I could switch mounts.
04-16-2019, 07:28 PM - 1 Like   #14
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ok so the sears 'm' arrived today but the aperture is stuck wide open (got it in a camera bundle that ended up quite lame)
anyways I switched out the rear parts....went together quite smoothly and registers as an 'A' lens.....I believe it would operate the aperture (maybe not correctly) if it worked.....
reckon I will try again if I get an operational 135 'm'.....

the good news is I can use this frankenstien on my K-50 that has aperture block failure since it is stuck wide open and use HSS with the af-360/cactus system...…
have a vivitar S1 28-105 that's stuck wide open and useful in this manner as well

so it worked but not in the manner I wanted...…….
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