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06-17-2007, 09:48 PM   #1
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help request with M42 lens

Just got a M42 screw mount lens for use on my dSLR bodies. I came to Pentax with the K and M series lenses and have never used the screw mount lenses. How can I tell the A/M switch is in Auto or Manual mode? Is the lens in Auto when the "A" is exposed (switch slid to cover up the "M"), or the "M" exposed (switch slide to cover the "A" position).

In use, does one focus with the switch covering up the "M" (aperture is wide open", then slide the switch to cover up the "A" (lens is stopped down), meter with the appropriate button (with lens stopped down), then take the shot?

Thanks for any help you can offer.

06-18-2007, 12:02 AM   #2
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Slide the switch so that the "M" or manual is exposed. You know you have the correct setting if the aperture stops down when you rotate the aperture ring.

To shoot. Set the camera to Av mode, focus and compose at maximum aperture, stop down the lens to what you want and take the photo. The camera will automatically meter the change in aperture, no extra button pushes required.

You can, of course, use manual exposure as well.

cheers

Greg
06-18-2007, 12:11 AM   #3
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>Is the lens in Auto when the "A" is exposed (switch slid to cover up the >"M"), or the "M" exposed (switch slide to cover the "A" position).
The "Exposed" is the one which becomes effective. So, you should expose "Manual" for dSLRs.

>In use, does one focus with the switch covering up the "M" (aperture is >wide open", then slide the switch to cover up the "A" (lens is stopped >down), meter with the appropriate button (with lens stopped down), then >take the shot?

You always leave it at "Manual". The "Auto" is for older screw mount film bodies.

The easiest way is to use these lenses in Av mode of the current dSLR's.
You may need to adjust exposure compensation for varying apertures; some experimentation is required.
06-18-2007, 12:56 AM   #4
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with my thread lenses the metering is ok up to around F8, if i want smaller aperture, i switch to manual. The histogram is of great help here!!

06-18-2007, 02:23 AM   #5
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QuoteOriginally posted by bc_the_path Quote
>Is the lens in Auto when the "A" is exposed (switch slid to cover up the >"M"), or the "M" exposed (switch slide to cover the "A" position).
Yes, The lens in Auto when the the A is exposed.
06-18-2007, 09:59 AM   #6
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Original Poster
Thanks to all for the clarification. Going to have to try it out tonight and see if I can infinity focus or not. Stupid me! Sold a "real" Pentax brand M42 adapter last year when I didn't think I'd ever use it.
06-19-2007, 01:56 AM   #7
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If you know beforehand what aperture you wish to use, you can set the switch to Auto and set your aperture on the ring. The iris will stay wide open. Focus, then just before shooting move the switch to Manual and the iris will close down to your pre-selected aperture.

Due to the adapter causing the lens to mount off-center, the switch comes out on top of the camera, right under the built-in flash, making it an awkward move. I have personally never found any use for the technique, but I mention it as a possibility and an idea for anyone who might find some use for it.
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