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02-05-2008, 09:12 PM   #1
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Screw mount to K mount adaptor?

Hey guys, I was interested in getting a Pentax/Asahi lens for my z-xm. I was wondering if I got the adapter to turn the screw mount to a k-mount would all my meters work? If not then do you guys have any other suggestions as far as getting a manual f1/4 lens? Thanks!

02-05-2008, 09:15 PM   #2
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QuoteOriginally posted by Wolf74 Quote
Hey guys, I was interested in getting a Pentax/Asahi lens for my z-xm. I was wondering if I got the adapter to turn the screw mount to a k-mount would all my meters work? If not then do you guys have any other suggestions as far as getting a manual f1/4 lens? Thanks!
The metering will work. The automatic stop down of the aperture will not. You will be using stop down metering with the M42 lens, as there is no way for the camera to hold the aperture open for metering. When you set the lens to f/8, that's what you will see through the viewfinder,, just as if you used the depth of field preview. Annoyingly enough, the M42 lens will probably work in aperture priority AE, whereas the M series lenses will not.
02-05-2008, 09:36 PM   #3
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Thanks for the info. But I'm not quite sure what you mean by stop down metering. Can ya explain a little?
02-05-2008, 09:43 PM   #4
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QuoteOriginally posted by Wolf74 Quote
Thanks for the info. But I'm not quite sure what you mean by stop down metering. Can ya explain a little?
It simply means that in order for you to get a correct light meter reading, you have to manually set the lens to f8. On the K mount there's a little lever that interacts with a lever in the body that tells the body that the lens is set to f8, on a M42 lens there's no such interaction, so you have to set the lens to what you want, which cuts down on the light going to the light meter.

02-06-2008, 01:15 PM   #5
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QuoteOriginally posted by Wolf74 Quote
Thanks for the info. But I'm not quite sure what you mean by stop down metering. Can ya explain a little?
Sorry for the delay - I was off line.

Stop down metering is an expression that means that you meter the exposure with the aperture actually at the setting you will use.

Suppose you have a 55/1.8 M42 lens on your dSLR. When you turn the aperture ring to f/11, the viewfinder will get dark; the aperture blades will actually take the f/11 position. In photo parlance, the lens is "stopped down". The mechancial connection is not there for the M42 lenses on a K mount camera, so the camera has no idea what the f/stop is set to.

The previous post said basically the same as the above. I just used some different words to perhaps help you understand the concept.
04-06-2008, 11:02 PM   #6
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Thanks again for all your help.
04-07-2008, 06:13 AM   #7
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Beware of what adapter you buy
make sure it can focus to INFINITY, a few of them will not work
04-07-2008, 06:45 AM   #8
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If you are interested in an original Pentax K mount to M42 adapter, I have one I'll sell. Just send me a private message and I'll tell you how to use it as well.

04-07-2008, 07:46 AM   #9
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M42 adapters

QuoteOriginally posted by titrisol Quote
Beware of what adapter you buy
make sure it can focus to INFINITY, a few of them will not work
To elaborate on this, some adapters have a large-ish flange that sits outside the lens mount. This added thickness prevents the lens from focusing at infinity. This may be okay if you are doing macro work, but it is not good for general photography.

The genuine Pentax adapter and the better third-party adapters fit entirely inside the camera lens mount opening, leaving a flush surface. Therefore, these adapters allow the lenses to focus to infinity normally.

I'm not very familiar with the ZX-M, but I did have its contemporary, the ZX-60, for a while. The ZX-60 will not function with any lens that does not have an "A" aperture setting, or with a lens that has the aperture set anywhere other than "A". This is not the A-M setting on screw-mount lenses.

If the ZX-M requuires the "A" setting on the aperture, the way the ZX-60 does, then you won't be able to use an adapter, because no screw-mount lens will have the setting.

Paul Noble
04-07-2008, 08:02 AM   #10
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Paul I'm fairly certain the ZX-M will work as seen in this chart:
The Pentax Camera Lens Compatibility Chart

The adapter with the flange is the following one:
https://www.pentaxforums.com/forums/attachments/pentax-slr-lens-discussion/66...-k-mount-2.jpg
https://www.pentaxforums.com/forums/attachments/pentax-slr-lens-discussion/66...-k-mount-1.jpg
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