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Old Dec 8, 2006, 9:34 AM   #1
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I have been looking at some Pentax-A 50mm 1.4/17 lens. From what I understand the A here is for auto aperture, and the M will denote manual aperture. Now My question is that if I get one of the lens with the M42 screw mount and the K adapter -- are thoese lens auto aperture or are they all manual?

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Old Dec 8, 2006, 9:39 AM   #2
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they would work as manual only.
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Old Dec 8, 2006, 9:41 AM   #3
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The M42 lenses can only be used in the M position since the aperture will not stop down otherwise. Beware, there are a very small number of M42 lenses that are auto only and therefore will not work on a K-mount camera (ran into that over 25 years ago with a Hanimex 35mm f2.8 lens that I sold because I could not use it with my (then) new Pentax ME Super).

The A in Pentax-A series lenses means something completely different, it means that the camera can set the aperture value automatically. A Pentax A lens will do everything but autofocus on a Pentax DSLR.


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Old Dec 8, 2006, 10:42 AM   #4
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To make it simplier, the M42's have a pin that goes in and out. The K mount uses a lever that goes up and down, so there is no mechanical connection with the camera when using M42 lenses. They take fine pictures, but are totally mechanical. By pressing the AE-L button you can set the correct shutter speed for the aperture you have the lens set at though, so that part still works like the M-seriesK mount lens would - Bruce
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