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03-08-2013, 12:03 PM   #1
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Help with Takumar Bayonet on the K-01!

Just got my wonderfully sharp Takumar Bayonet 135/2.5 today. I am using it on my K-01 but I can't seem to get the green button to work? Am I missing something here? Do I have to use it in M mode and not AV mode? When I focus on something at f/2.5 and hit the green button nothing seems to happen and when I change the aperture to f/5.6 and hit the green button nothing changes. The manual is not really helping me much so if someone would help me I would be most grateful.

03-08-2013, 12:12 PM   #2
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QuoteOriginally posted by treebeard Quote
Do I have to use it in M mode and not AV mode?
In a word, yes.

Manual bayonet lenses have always worked this way on Pentax DSLRs, and it's true on the K-01 also.

M42 screwmount lenses -- the truly manual ones at least, and ones with a Manual/Auto switch like many Takumars -- work in Av mode because they're always stopped down.

I don't think there's any technical reason why Av mode COULDN'T work on a manual bayonet lens -- and I think someone (THoog?) has a hack to enable it -- but I have never bothered, because M mode plus green button has always worked fine for me.

(Actually, I can think of one reason: stopping down to take an exposure measurement right before the capture will mess with the shutter operation, and probably lengthen shutter button latency. It would need to stop down with the shutter open, measure, then arm the shutter and fire it. Ordinarily, metering is going on all the time, so when you hit the shutter button, it just stops down and arms the shutter at the same time.)

EDIT: Here's a thread where THoog talks about the taped-contact hack. It enables TAv (auto ISO) in M mode at least, but I don't know about Av mode.

Last edited by Quicksand; 03-08-2013 at 12:21 PM.
03-08-2013, 12:13 PM   #3
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QuoteOriginally posted by treebeard Quote
Just got my wonderfully sharp Takumar Bayonet 135/2.5 today. I am using it on my K-01 but I can't seem to get the green button to work? Am I missing something here? Do I have to use it in M mode and not AV mode? When I focus on something at f/2.5 and hit the green button nothing seems to happen and when I change the aperture to f/5.6 and hit the green button nothing changes. The manual is not really helping me much so if someone would help me I would be most grateful.
Yup, you need to be in M mode. Av mode will only work with lenses that have a manual diaphragm.

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03-08-2013, 12:35 PM   #4
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Whenever this question comes up I link to this thread:
https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...k-x-k-7-a.html

Make sure you have enabled aperture ring and the lens is fully mounted (should click into place). When you hit the green button the camera meters. It should stop down to the selected aperture and adjust the shutter speed to what it deems is the right value.
If you have Av mode or auto iso, then the camera will always shoot wide open, but it will also meter continuously, so this can be useful. Just check the screen to see whether it says M or Av. It will default to Av mode in all modes, other than M. And maybe video, not quite sure how it handles that.
But honestly, with that lens, I suggest you just set it to M mode, shutter speed to 1/250 and manually adjust aperture on the lens and ISO sensitivity on the camera (leave it low, except for when shooting in dark places or indoors). If you use SR (make sure you input the correct number) and have a steady hand, you can probably get away with a slower shutter speed as well.
Good luck!

03-08-2013, 12:42 PM   #5
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Thanks for the responses. I was in Av mode so that's why the shutter speed was not changing when I changed the aperture. It's
been awhile since I have used a lens w/out the A setting. I will have to go back and re-read the article, which I did and it all came back. It's working wonderfully now and it's a great lens paired with my 50/1.7!

Last edited by treebeard; 03-08-2013 at 05:34 PM.
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