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02-05-2016, 08:23 PM   #1
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Green button and manual/K-mount lens

I happen to have a 50mm 1.7 Pentax-M lens in my legacy collection, and I finally got around to trying it with my new/used K-r today.

I've got the dial on "M" and I think that the way this is working is that if I set the lens, to, say, f8, then press the green button, the K-r automatically selects the correct shutter speed.

That's what it seems like anyway.

Is that correct?

Also, re. focussing in this case (with a Pentax-M), I noticed that when I get the lens focused a small red square appears in the viewfinder. Is that indicating that I'm in focus in the center? So, can I rely on that red square rather than trying to actually see that the image in the viewfinder is sharp (eyes are getting really bad)?

Also, one more thing: I a bunch of M42 lenses and also a couple of M42-to-K-mount adapters. Would the M42 lenses work the same way as above?

Thanks,
Jim

EDIT: One more question: Assuming that the above is correct as far as how the green button works, what do I do in situations where I want to increase exposure (e.g., in a backlit situation)?


Last edited by ohaya; 02-05-2016 at 08:24 PM. Reason: Added one more ques
02-05-2016, 08:47 PM   #2
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Sounds like you've got the hang of it!

QuoteOriginally posted by ohaya Quote
Also, one more thing: I a bunch of M42 lenses and also a couple of M42-to-K-mount adapters. Would the M42 lenses work the same way as above?
Yes, except Av mode would also work since M42 lenses have manual diaphragms. In other words, since the viewfinders darkens as you stop down, you don't need to stop the lens down to meter using the green button. You can still use the green button in M mode if you want to, though - the end result will be the same

QuoteOriginally posted by ohaya Quote
Also, re. focussing in this case (with a Pentax-M), I noticed that when I get the lens focused a small red square appears in the viewfinder. Is that indicating that I'm in focus in the center? So, can I rely on that red square rather than trying to actually see that the image in the viewfinder is sharp (eyes are getting really bad)?
The AF confirmation has a fairly high tolerance, so I would verify that the image is in focus. When on a tripod, you can of course use live view which will make things even easier.

Adam
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02-05-2016, 08:56 PM   #3
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QuoteOriginally posted by Adam Quote
Sounds like you've got the hang of it!



Yes, except Av mode would also work since M42 lenses have manual diaphragms. In other words, since the viewfinders darkens as you stop down, you don't need to stop the lens down to meter using the green button. You can still use the green button in M mode if you want to, though - the end result will be the same



The AF confirmation has a fairly high tolerance, so I would verify that the image is in focus. When on a tripod, you can of course use live view which will make things even easier.


Hi,

Thanks for all the answers. I was a little worried about how "unnatural" using the old lenses would be, but with the way it works, it actually feels pretty natural, esp. for someone who learned photography with a hand held light meter (or with no meter at all )...
02-05-2016, 09:27 PM   #4
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QuoteOriginally posted by ohaya Quote
EDIT: One more question: Assuming that the above is correct as far as how the green button works, what do I do in situations where I want to increase exposure (e.g., in a backlit situation)?
Just adjust your aperture with the ring or your shutter speed with the e-dial after you hit the green button, a lot like the manual cameras of old. Also note that auto bracketing and exposure compensation also work with this configuration.

02-05-2016, 09:33 PM   #5
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QuoteOriginally posted by KC0PET Quote
Just adjust your aperture with the ring or your shutter speed with the e-dial after you hit the green button, a lot like the manual cameras of old. Also note that auto bracketing and exposure compensation also work with this configuration.
Ahh, I forgot, I'm in "manual mode", i.e., I get to control the opening!!
02-05-2016, 10:29 PM   #6
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(As I don't think your question about ev adjust in M mode was answered) I believe the K-r works like the K-x w/ regards exposure compensation--namely:
-- For pre-A K mount lenses in M mode it will not do it (my K-20d & K-5 will)--so after green button adjust aperture ring or shutter speed by the ev adjustment you want.
-- M42 and A lenses can meter in AV mode and in AV mode the user can set an ev adjustment value.

Sorry KCOPET answered this/did not mean to duplicate it.
02-06-2016, 07:13 AM   #7
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NP, but I think that is additional information. I don't have a K-r, so I just assumed it worked like other models. Does auto bracketing work with pre-A K mount lenses in M mode?
02-06-2016, 11:43 AM   #8
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I've been trying Av instead of M/Manual, and one thing I'm curious about.

When I am in M and click the green button, I hear a "clack", like the mirror moving when I am taking a pic and it sets the speed.

When I am in Av, it seems like the speed changes as I move the camera around and when I click the green button, but no "clack" sound.

In other words, it seems like in Av mode, it measures the light without moving the mirror, but in M mode, it has to move the mirror to take the measurement? I'm not sure if I know what I'm talking about though ...

02-06-2016, 02:44 PM   #9
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Also check menu!

When using these lenses you have to check one special item in the menu. At least in my case, trying without this adjustment I ended up using full aperture regardless of how I turned the aperture ring on the lens.

On my Pentaxes: Menu, C, item 26 or thereabouts, "Using Aperture Ring" check "Enable". Then the aperture you select on the lens works very well with "Manual" and green button.

(Congratulations on that lens! I think it gives very sharp but still not harsh pictures and negligible distorsions. A litte bit sensitive to flare but no big "problem".)
02-06-2016, 03:12 PM   #10
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QuoteOriginally posted by Mans Hagberg Quote
When using these lenses you have to check one special item in the menu. At least in my case, trying without this adjustment I ended up using full aperture regardless of how I turned the aperture ring on the lens.

On my Pentaxes: Menu, C, item 26 or thereabouts, "Using Aperture Ring" check "Enable". Then the aperture you select on the lens works very well with "Manual" and green button.

(Congratulations on that lens! I think it gives very sharp but still not harsh pictures and negligible distorsions. A litte bit sensitive to flare but no big "problem".)

Hi,

I checked that setting (the aperture ring one) and on this K-r, it was already set at 2/enabled.

Any idea about the M vs. Av and the mirror motion questions?

Thanks,
Jim
02-06-2016, 05:18 PM   #11
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Hi,

I recently found I had an old Soligor 28mm/f2.8 lens, and then I just found a long-lost T-mount adapter tonight, so I was messing with the "new" lens and my K-r.

I tried it in Av mode (focus with lens open, stop down lens, press green button, fire), but it seemed like when I used that and the green button, it was underexposing. On the other hand, if I did the same steps in M/manual mode (focus with lens open, stop down lens, press green button, fire), it looks good. I'm attaching two pics. The first is using Av mode and the 2nd is using Manual mode.

What am I doing wrong in Av mode? Or is Av mode not supposed to work with this completely manual T-mount/M42 lens?
Attached Images
View Picture EXIF
PENTAX K-r  Photo 
View Picture EXIF
PENTAX K-r  Photo 
02-06-2016, 05:29 PM   #12
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ohaya, I believe what you are hearing is the stop down mechanism kicking in, not the mirror. When you hit the green button, it activates the aperture lever on the lens to stop down the lens, then takes a meter reading. It is similar to the old "automatic" M42 cameras (like Mamiya Sekor or Pentax Spotmatic) where you pushed in the film advance in or turned on the metering switch to stop down the lens, set the meter, then let go to focus, if you ever used one of those cameras.

If I understand it right the AV mode will do live metering, but only for wide open shooting. I don't use AV mode with M lenses so I am not familiar with exactly how it works.
02-06-2016, 05:33 PM   #13
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QuoteOriginally posted by KC0PET Quote
ohaya, I believe what you are hearing is the stop down mechanism kicking in, not the mirror. When you hit the green button, it activates the aperture lever on the lens to stop down the lens, then takes a meter reading. It is similar to the old "automatic" M42 cameras (like Mamiya Sekor or Pentax Spotmatic) where you pushed in the film advance in or turned on the metering switch to stop down the lens, set the meter, then let go to focus, if you ever used one of those cameras.

If I understand it right the AV mode will do live metering, but only for wide open shooting. I don't use AV mode with M lenses so I am not familiar with exactly how it works.
Oh, so with fully manual lenses, if I use Av mode, then the lens will always have to be full open?
02-06-2016, 06:37 PM   #14
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My K-5 does following I believe, and pretty sure my K20d and K-x do likewise.
-- In AV and M mode the lens is not stopped down on taking exposure reading--if lens set to A setting, and proper exposure at taking f stop is made. The advantage is more light is being measured.
-- In AV mode if non A lens, or A lens not set to A, it take the exposure wide open and does not correct for the desired f stop (it does not know about it).
-- In M mode if K lens--and not A lens, or A lens not set to A, it stops lens down to take the exposure
02-07-2016, 06:47 PM   #15
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Hi,

I'm still confused about Av (or Av is not working for me), with full manual (like an M42) lens.

If I put the mode to Av, I thought all I had to do was leave the lens wide open, e.g., with the 28mm Soligor I set it to f2.8, and put the mode to Av. Whether or not I hit the green button, and then shoot, it looks like it's coming in underexposed (too dark).

Can someone explain how I should use Av with such an manual lens?

Thanks,
Jim
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