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01-17-2015, 08:28 AM   #1
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Noob to M42 lenses -- quick question

I have acquired my 1st M42 screw-mount lens and am a total noob to this type of lens. I have a couple of quick questions regarding use of these lenses ...


1. What is the pin on the back side of the lens for? Is it used at all on a modern Pentax DSLR?
2. I have just started shooting some test shots and am using in AV mode. Any recommendation on shooting M42 Takumar) lenses?


Thanks!!


Last edited by ripper2860; 01-17-2015 at 08:42 AM.
01-17-2015, 08:35 AM - 1 Like   #2
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I think this should answer your questions

https://www.pentaxforums.com/forums/54-pentax-lens-articles/110657-how-use-me...k-x-k-7-a.html
01-17-2015, 08:37 AM   #3
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The pin on the back is to close the aperture when the lens is set to Auto. It is not used by any camera other than a screwmount camera.

If the lens does not have an Auto/Manual (A/M) switch you have to gimmick the pin to close the aperture, or use an adapter that has an internal flange to depress the pin.
01-17-2015, 08:39 AM   #4
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Quick answers:
1. No.
2. Make sure the "MAN./AUTO" switch is showing "MAN." - this allows you to stop the lens down. Otherwise you'll be shooting it wide open all the time.
3. Have fun!

01-17-2015, 08:48 AM   #5
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I appreciate the info. I failed to mention that I am musing a M42-K adapter (Fotodiox) that supports infinity focus. The lens does have an A and M switch. I've been using it in A mode to focus (to maximize light to through the VF (unless shooting at or near wide-open)) and then switching to M prior to shooting to stop-down and meter/shoot. So far I find it easier than an M with green-button stop-down metering -- it just seems more natural.


The reference link/article specifies M mode. Any reason why AV mode would not work ?


Again -- thanks!!

Last edited by ripper2860; 01-17-2015 at 08:56 AM.
01-17-2015, 09:12 AM   #6
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QuoteOriginally posted by ripper2860 Quote
I appreciate the info. I failed to mention that I am musing a M42-K adapter (Fotodiox) that supports infinity focus. The lens does have an A and M switch. I've been using it in A mode to focus (to maximize light to through the VF (unless shooting at or near wide-open)) and then switching to M prior to shooting to stop-down and meter/shoot. So far I find it easier than an M with green-button stop-down metering -- it just seems more natural.


The reference link/article specifies M mode. Any reason why AV mode would not work ?


Again -- thanks!!
Av works with m42s that you can stop down, yes. Whereas bayonet M-type lenses will not stop down ever unless the camera is in (M)anual. However, the metering can become somewhat inaccurate as you stop down (unless you are in live view), so you may want to use EV compensation depending on the apertures you are using. Just do lots of shooting and experimentation...
01-17-2015, 09:17 AM   #7
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Thanks!! I've noticed the metering inconsistencies with my manual M, and K lenses, as well as a preset T2 lens I currently have. Seems to be a wide-spread issue not limited to M42s. It's tricky as the amount of EV compensation needed varies with aperture and the lens. I may have to resort to bracketed shots, but so far I've been able to address in PP.
01-17-2015, 09:29 AM   #8
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I have tried to address a lot of this on my pages:

Using manual focus lenses on Pentax (and Samsung)DSLR's

haven't finished the third page yet which is supposed to be M42 stuff in detail however most is already mentioned on pages 1 and 2, and also touched on on my new page on t-mount lenses

How to use t-mount, preset lenses.

which isn't linked yet and I haven't done pics for
I also contributed this here:
https://www.pentaxforums.com/forums/116-pentax-k-r/271872-tests-plated-vs-pai...r-whats-t.html

comments welcome

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