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05-21-2008, 12:56 PM   #1
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M lenses and metering

So here is the thing:

Today I tried my M 50/1.7 lens on my MZ-7 film SLR. I put the camera into Av mode and turned the aperture ring on the lens. Surprisingly, the camera responded with different shutter speed values. What am I missing here? The DSLR does not do that, because the aperture is wide open until you press the shutter release or A/E lock button in M mode.

I know, that when you use M42 lenses, you actually change the aperture opening when turning the aperture ring. But of course you notice this as the viewfinder is getting darker when stopping down the lens.
How in the world does the MZ film camera know, that the aperture has been changed? I didn't notice any darkening of viewfinder image when I stopped down the lens.
Can anyone explain this to me, please?

05-21-2008, 01:50 PM   #2
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The MZ-7 has the original KAF2 mount. The digitals have a 'crippled' version, which basically means they are unable to read the aperture value mechanically, presumably through the aperture lever.

In theory, if the digital bodies were told the aperture wide-open and the aperture when stopped down, it didn't have to check the exposure stopped down.
(Which is what the A lenses do.)
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