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01-26-2009, 11:23 AM   #1
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Will the K20D meter with M lenses attached?

Sorry for this (probably) stupid/boring/old/etc. question, but surprisingly I can't find an answer neither here on the forum, nor in the camera manual...

Anyway, the question is:

Will the K20D automatically set the exposure in Av mode, when the M lens is attached and the aperture is set manually?

Thanks.

01-26-2009, 11:25 AM   #2
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Correct me if i'm wrong, but I think that Av mode works properly if you are using the biggest aperture. But if you stop down the lens, you'll have to meter manually.

grets

Juho
01-26-2009, 11:36 AM   #4
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QuoteOriginally posted by igor Quote
Sorry for this (probably) stupid/boring/old/etc. question, but surprisingly I can't find an answer neither here on the forum, nor in the camera manual...

Anyway, the question is:

Will the K20D automatically set the exposure in Av mode, when the M lens is attached and the aperture is set manually?

Thanks.
If you are in other than M mode, the camera will automatically default to AV for all non-A mount lenses. With a Pentax-M lens, this will mean metering and taking at full aperture only, regardless of aperture ring setting.

Steve

01-26-2009, 11:49 AM   #5
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QuoteOriginally posted by igor Quote
Sorry for this (probably) stupid/boring/old/etc. question, but surprisingly I can't find an answer neither here on the forum, nor in the camera manual...

Anyway, the question is:

Will the K20D automatically set the exposure in Av mode, when the M lens is attached and the aperture is set manually?

Thanks.
all pentax cameras are the same, in AV mode they expose withthe lens wide open, not manual way to stop down with M lenses.

In manual mode, push green button to set shutter to "correct" speed for stopped down apature, or use the DOF preview to set shutter pseed manually but with metering activated so you can see over/under exposure.

When I say correct, K10d and K20D have some exposure issues with manual exposure lenses.

see attached


https://www.pentaxforums.com/forums/241716-post69.html
01-26-2009, 12:21 PM   #6
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Thanks guys, I think I got the picture.

Still, Lowell, have I got it correctly: every time I change manually the aperture on the M lens I have to press the green button before taking the picture? to get the correct exposure that is.
Why the same effect can't be achieved by just pressing the shutter button half-way??
01-26-2009, 01:31 PM   #7
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QuoteOriginally posted by igor Quote
Thanks guys, I think I got the picture.

Still, Lowell, have I got it correctly: every time I change manually the aperture on the M lens I have to press the green button before taking the picture? to get the correct exposure that is.
yes
QuoteQuote:
Why the same effect can't be achieved by just pressing the shutter button half-way??
because the half press of the shutter only activates focus functions and metering, not stop down of the lens.

it would add a lag to shutter release if it was done.
01-26-2009, 02:08 PM   #8
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Thanks again Lowell, it's clear now.

01-26-2009, 04:42 PM   #9
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QuoteOriginally posted by igor Quote
Still, Lowell, have I got it correctly: every time I change manually the aperture on the M lens I have to press the green button before taking the picture? to get the correct exposure that is.
That's one way. But another is to simply trust that if you open up the aperture one stop, you can speed up the shutter one stop to compensate, and so on. I do this all the time. I might also of a DOF preview to check to see if the meter agrees with me - I check the meter in the DOF quite often, actually, to monitor light changes.
01-27-2009, 12:35 AM   #10
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QuoteOriginally posted by Lowell Goudge Quote
yes because the half press of the shutter only activates focus functions and metering, not stop down of the lens.

it would add a lag to shutter release if it was done.
In fact, no, as the camera has to stop down anyway to take the pic...
So, the only downside to such a feature would be the darkened viewfinder during half-press (that and the battery drain!).

But a simpler solution would have been to do the metering on shutter release, once the lens is stopped down... I'm sure it would not take too much time...
01-27-2009, 06:03 AM   #11
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QuoteOriginally posted by dlacouture Quote
In fact, no, as the camera has to stop down anyway to take the pic...
So, the only downside to such a feature would be the darkened viewfinder during half-press (that and the battery drain!).

But a simpler solution would have been to do the metering on shutter release, once the lens is stopped down... I'm sure it would not take too much time...
but the camera does not need to be completely stopped down prior to the movement of the mirror, where as here it would, Presently stopping down can be done in parallel tomoving the mirror, where as your proposal would require stop down to be always before moving the mirror because metering is done off the focusing screen.

Aside from that point, given the issue with metering on the K10SD and K20D anyway with manual lenses it is a lot of effort for nothing.
01-27-2009, 06:13 AM   #12
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This is why M42 lenses are so much simpler to use on the crippled K-mount than are M lenses.
01-27-2009, 06:29 AM   #13
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QuoteOriginally posted by Mike Cash Quote
This is why M42 lenses are so much simpler to use on the crippled K-mount than are M lenses.
to some extent, having bought a couple now, I have to agree,

put it in Av mode, add what ever compensation factor yo need for metering error and just go out and shoot.

especially with 35 and 28 mm lenses the DOF makes it almost unnecessary to focus, and even stopped down to 5.6 (my lenses are F2 and F2.5) the view finder is just as bright as a kit lens so focusing is not a big deal anyway.

I still like the first generation K mounts over the M42's but would take an M42 over most SMC-M lenses just because the M series feel cheap
01-27-2009, 04:52 PM   #14
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QuoteOriginally posted by dlacouture Quote
So, the only downside to such a feature would be the darkened viewfinder during half-press (that and the battery drain!).
Um, that and the fact that the whole point of "M" mode is that you set the exposure and the camera doesn't change it. I sure as heck don't want the camera picking a new shutter speed for me every time I press the shutter button! It doesn't do that with DA lenses; it better not with M lenses!

Such a thing could have been implemented for Av mode, of course.
01-28-2009, 02:05 AM   #15
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NIkon does it in A mode, you put any non-AF lens (AI, AIS) on a camera (D2x, D200 or later) and shoot. Camera meters automatically just fine.
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