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11-23-2021, 03:45 PM   #1
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Turning a Pentax M lens into a Pentax A lens

I know it sounds a bit far fetched, but I remember seeing a post about it somewhere. Also I recently ran into an item online which had undergone such conversion.
I have searched the forum thoroughly but to no success, I suspect I haven't picked the right words to do so.
Can anyone help me get to such article if it exists?
Thank you in advance!

11-23-2021, 03:52 PM - 1 Like   #2
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converting M lens to A lens - PentaxForums.com
11-23-2021, 04:39 PM - 1 Like   #3
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It does sound far fetched, because it would require the skills of an instrument maker and access to a machine shop Unless, as a matter of terminology it would simply mean the repair of a broken A-series lens using some compatible donor optical and mechanical parts from an M-series lens, which could be possible within limits.
QuoteOriginally posted by steephill Quote
I looked through that thread and it appears that at best the efforts were only partly successful. They were not complete conversions.

What lens did you have in mind? Unless it is some very special lens such as an extreme telephoto, A-series lenses in working order are available relatively cheaply on Ebay.
11-23-2021, 05:52 PM - 1 Like   #4
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Seems more trouble than it is worth. Why not just buy a working A lens? You would have to swap out the entire diaphragm mechanism.

Aren't there other threads on exposure issues with M and K lenses where you simulate the A contacts. Something to do with the proportional movement of the aperture lever in relation to iris opening?

11-23-2021, 08:30 PM   #5
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QuoteOriginally posted by Not a Number Quote
Seems more trouble than it is worth. Why not just buy a working A lens? You would have to swap out the entire diaphragm mechanism.

Aren't there other threads on exposure issues with M and K lenses where you simulate the A contacts. Something to do with the proportional movement of the aperture lever in relation to iris opening?
M lens aperture lever movement isn’t proportional to the aperture area. A series lens aperture lever movement is.
11-24-2021, 12:46 AM   #6
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QuoteOriginally posted by shyrsio Quote
Also I recently ran into an item online which had undergone such conversion.
Don't know if that is the question, but personally I would NOT buy something like this.
Other than that, have fun! (but please don't massacre innocent lenses in the process)
11-24-2021, 01:17 AM   #7
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As mentioned above has a simple 'conversion' by creating the conductive /non-conductive pattern on the lens some issues because of the differences in the M and A series aperture levers.
Close to wide open it won't be that obvious, but the further you stop down the lens, the greater your discrepancies from the intended exposure will be

11-24-2021, 03:18 AM   #8
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QuoteOriginally posted by othar Quote
Close to wide open it won't be that obvious, but the further you stop down the lens, the greater your discrepancies from the intended exposure will be
Someone on another thread who did the "simple" conversion said they did not mind that limitation because they always shot wide open (or nearly). But if you are choosing a lens aperture you must be over-riding the camera's Program mode algorithm and effectively using it in Aperture Priority Auto mode or Manual mode, both of which M-series lenses already allow, and all that will have been achieved is to enable aperture control from the the thumbwheel on the camera (if a DSLR), as well as (or instead of*) the ring on the lens, and the thumbwheel will not even control the smaller apertures accurately, as others have pointed out.

*Depending on how the conversion is done.
11-24-2021, 03:25 AM   #9
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QuoteOriginally posted by Lord Lucan Quote
It does sound far fetched, because it would require the skills of an instrument maker and access to a machine shop Unless, as a matter of terminology it would simply mean the repair of a broken A-series lens using some compatible donor optical and mechanical parts from an M-series lens, which could be possible within limits.

I looked through that thread and it appears that at best the efforts were only partly successful. They were not complete conversions.

What lens did you have in mind? Unless it is some very special lens such as an extreme telephoto, A-series lenses in working order are available relatively cheaply on Ebay.
I was thinking of converting the K 50/1.2. I know, I know I shouldn't. but I wouldn't put my hands on it if I wasn't 100% certain of what I did. Its quite difficult to reach the aperture ring when the camera is mounted on the K1.

---------- Post added 11-24-21 at 03:31 AM ----------

QuoteOriginally posted by steephill Quote
Thank you very much!
I was looking for something like a detailed guide, but this gave me an idea of how its done. I see its quite problematic though and at the moment I wouldn't dare touch my precious K 1.2/50.
11-24-2021, 03:52 AM   #10
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Perhaps the K-1 mark III will have the stop-down meter function in Av mode for non-A MF lenses taken from the K-3 mark III. I doubt you'll see it in a firmware update for the K-1/K-1ii.

But that doesn't solve the difficulty of accessing the aperture ring.
11-24-2021, 04:17 AM - 1 Like   #11
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The "K" and the "A" Version of the 1.2/50 mm share the same optical design.
Thus I would try to get a 1.2/50 A and sell the 1.2/50 K.
11-25-2021, 04:58 PM   #12
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QuoteOriginally posted by Not a Number Quote
Perhaps the K-1 mark III will have the stop-down meter function in Av mode for non-A MF lenses taken from the K-3 mark III. I doubt you'll see it in a firmware update for the K-1/K-1ii.

But that doesn't solve the difficulty of accessing the aperture ring.
I'm sorry, am I missing something? If you're talking about stop down metering using the green button it's already available in the K-1. Is there any other option that the K3 iii has in this field that I dont know of, other than manually setting the aperture value for the exif? (Please let it be the Aperture simulator reader)

---------- Post added 11-25-21 at 04:59 PM ----------

QuoteOriginally posted by Papa_Joe Quote
The "K" and the "A" Version of the 1.2/50 mm share the same optical design.
Thus I would try to get a 1.2/50 A and sell the 1.2/50 K.
The price of the A version is almost double the price of the K version for some reason, so the upgrade seems unlikely anytime soon.
11-26-2021, 12:22 AM   #13
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QuoteOriginally posted by shyrsio Quote
I'm sorry, am I missing something? If you're talking about stop down metering using the green button it's already available in the K-1. Is there any other option that the K3 iii has in this field that I dont know of, other than manually setting the aperture value for the exif? (Please let it be the Aperture simulator reader).
I think when using Av mode with K and M lenses the K-3iii now stops down to the chosen aperture on the aperture ring (by doing a stop down metering on its own)
11-30-2021, 06:34 AM   #14
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QuoteOriginally posted by Not a Number Quote
Seems more trouble than it is worth. Why not just buy a working A lens? You would have to swap out the entire diaphragm mechanism.
Indeed, apart if the person sees this as a fun project, it would be simpler to just get an A lens.
11-30-2021, 09:16 AM   #15
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One can knock oneself out trying; many did in the early days of Pentax Forums. There is no way around the lack of proportional aperture actuation in the M lens.


Steve
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