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04-04-2012, 08:55 PM   #1
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Pentax M Series Work in AV Mode (With Limited Functions)

I'm sure that a lot of other people already know this, but I didn't until a couple of days ago. This post is meant for people, like me, that may have been confused about the compatibility of my DSLR and m series lenses.

For months now, I was under the impression that if I got an M series lens, I would only be able to use it in manual mode. You can imagine my joy and delight when I got my first m lens and accidentally put the camera in AV mode only to discover that it does work. I think what confused me was reading this:

-Screwmount lenses may also be used in Av mode since they are always stopped down to the aperture you will be shooting at (unlike M&K lenses, which are stopped down only when the shutter is released or when you meter as described above).

from this article: https://www.pentaxforums.com/forums/pentax-lens-articles/110657-how-use-meter...-x-k-7-a.html?

I'm not really sure if that quote is misleading, or if my limited understanding just didn't really allow me to understand. I'm pretty sure I misunderstood.

I should mention that you do have to manually set the aperture using the aperture ring on the lens, but the camera does set the shutter speed for you once you've done this. Another thing to note is that the camera will not automatically compensate when using flash (or I haven't figured out how to do it) so all of the shots are extremely over exposed when using flash (I'm sure this can be corrected with manual flash settings, but I'm trying to point out the lack of automatic function).

Again, I'm sure that this is not a revelation for most people, but if this helps one confused soul it was worth the time writing it up.

04-04-2012, 09:12 PM   #2
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QuoteOriginally posted by reivax Quote
For months now, I was under the impression that if I got an M series lens, I would only be able to use it in manual mode
"M" series K-Mount lenses only work in "Hyper Manual" mode, in "AV" mode it will always shoot wide open no matter what aperture you have set on the ring.
04-04-2012, 10:11 PM   #3
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When I use my K- or M-series lenses on my K20D, I'll often leave the mode dial at TAv, which is right next to M (hyper-manual). Such non-A-type lenses cause the camera to default to Av when the dial is set to any Auto mode, such as TAv. I'll set the aperture to around f/4-f/8. I shoot the lens wide-open in TAv/Av; then, if I need to stop-down, I just flick the dial to M and hit the Green button. It's sort of like a quick-shift for the aperture when I'm in a hurry. With a dSLR that lacks TAv, just leave it at Av for the same trick.
04-05-2012, 12:16 PM   #4
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QuoteOriginally posted by reivax Quote
For months now, I was under the impression that if I got an M series lens, I would only be able to use it in manual mode. You can imagine my joy and delight when I got my first m lens and accidentally put the camera in AV mode only to discover that it does work.
It "works" only in the sense that you do in fact get a picture. But the aperture ring is being completely ignored - you get exactly the same picture whether you set it to f/2.8 or f/22. Same aperture, same shutter speed, same picture. Most people would call that "not working". But true, it does have its occasional value if you know you are only planning on shooting wide open. That is, if you have no intention of *using* the aperture ring for anything but decoration.

04-05-2012, 02:29 PM   #5
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Well that is good to know. I guess it's back to the "learning" board for me. I'm just curious if anyone can explain why it would work with m42 lenses and not with M lenses.
04-05-2012, 05:37 PM   #6
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QuoteOriginally posted by reivax Quote
Well that is good to know. I guess it's back to the "learning" board for me. I'm just curious if anyone can explain why it would work with m42 lenses and not with M lenses.
Because M42 lenses don't have the PK mechanical aperture linkage. With an M42 or a PK-zero (no linkage) lens, you set the aperture and it stays there while you peer through the viewfinder. This can make shooting stopped-way-down rather tricky. I took my SuperTak 35/3.5 out for a walk today in bright desert-mountain sunshine. I left it at f/16 and pretty much had to guess at the compositions.

An M lens has the mechanical linkage. On non-crippled cameras, like film SLRs and the *ist's, the mount (so I'm told) could sense the lens' aperture setting via that linkage. Our newer crippled-mount dSLRs can't do that. So if you're not in M mode, the aperture stays wide open. Go into M mode and hit the Green button, and the camera stops-down the lens for metering and subsequent exposures.

Hope this helps!
04-05-2012, 06:23 PM   #7
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QuoteOriginally posted by RioRico Quote
Our newer crippled-mount dSLRs can't do that. So if you're not in M mode, the aperture stays wide open. Go into M mode and hit the Green button, and the camera stops-down the lens for metering and subsequent exposures.

Hope this helps!
It does help. Thanks. I know this has been discussed, but I've never understood what makes our mounts "crippled". Is this on purpose for some type of added benefit? Or is this a design error that has not been fixed?
04-05-2012, 06:42 PM   #8
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While we can make a Pentax digital camera expose (relatively) correctly using a non-A lens, we must take the extra step of Green-Button or DoF-lever metering. This isn't a design error. It is an intentional feature designed to allow those of us who non-A lenses use them, while at the same time encouraging the purchase of new lenses.

We should be happy Pentax built-in the Green Button metering implementation.

04-05-2012, 07:03 PM   #9
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So why is it called a "crippled mount"?
04-05-2012, 07:15 PM   #10
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Doesn't have an aperture coupling lever.

Under the General heading at the top of this page you can find everything you ever wanted to know about the K Mount (and lots you didn't want to know).

Here is the direct answer to your question
04-05-2012, 07:58 PM   #11
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I got tired of using the metering button to keep checking the exposure I just removed the stop down lever on the lens, now it works like my screw mount lenses and I can use the M lens in Av mode just fine. Obviously as you stop the aperture down the view gets darker, but I have been using cameras since the early 80s and I am used to it.
04-05-2012, 08:43 PM   #12
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QuoteOriginally posted by BirdDude007 Quote
I got tired of using the metering button to keep checking the exposure I just removed the stop down lever on the lens, now it works like my screw mount lenses and I can use the M lens in Av mode just fine. Obviously as you stop the aperture down the view gets darker, but I have been using cameras since the early 80s and I am used to it.
No need to butcher your lens like this! You just have to drill a second locking groove halfway from the original one, so the lens locks "sideway" in the mount, and the aperture lever is not engaged by the camera.
And if you want to use the lens in its intended M-lens behavior (either on your DSLR or your film SLR), then just use the original locking groove, turning the lens fully into the mount...

I've seen so much lenses savagely tortured this way, I'm honestly thinking about creating the PETL!!!
04-05-2012, 09:16 PM   #13
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QuoteOriginally posted by dlacouture Quote
I'm honestly thinking about creating the PETL!!!
Some time ago I tried to start PETAL for artificial lifeforms, but nobody admitted to being robotic. [References to political candidates deleted.]
04-07-2012, 06:31 AM   #14
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QuoteOriginally posted by dlacouture Quote
No need to butcher your lens like this! You just have to drill a second locking groove halfway from the original one, so the lens locks "sideway" in the mount, and the aperture lever is not engaged by the camera.
And if you want to use the lens in its intended M-lens behavior (either on your DSLR or your film SLR), then just use the original locking groove, turning the lens fully into the mount...

I've seen so much lenses savagely tortured this way, I'm honestly thinking about creating the PETL!!!
I did it in a way so that I can return it back into its original condition, Besides...I will never get rid of this lens, I have had it since the 70s/80s (most of my life) so it is sentimental like my ME Super is to me.
04-07-2012, 06:53 AM   #15
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QuoteOriginally posted by BirdDude007 Quote
I did it in a way so that I can return it back into its original condition, Besides...I will never get rid of this lens, I have had it since the 70s/80s (most of my life) so it is sentimental like my ME Super is to me.
Ditto, did the same to mine, kept all the screws and parts, no problem, even removed the aperture ring ball. If you are used to the old pre-set lenses, you get to know more or less at what aperture you are by just looking at how dark the viewfinder becomes while you set the aperture, thus making it in a sort of pre-set lens.
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