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05-17-2011, 09:27 AM   #1
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Convert pentax-m to pentax-a?

I recall someone talking about modifying a pentax k or pentax-m lens to function as a pentax-a lens on a dslr. Is there a way of modifying it without permanently altering it? Or can I buy lens backs to convert a -m to -a?

05-17-2011, 09:33 AM   #2
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yes and no, you can do it technically though the aperture lever movement in non-A lenses might be non-linear and hence the conversion may not work as expected. However, if you are only shooting wide open, you will gain on flash metering.
05-17-2011, 10:42 AM   #3
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I converted a ricoh XR Rikenon 50mm F2 to KA mount, as a trial, (the lens is only worth about $30 and I had a K50/1.4 so it was no loss)

to do the conversion, I obtained some pins from a connector manufacturer who supplied pins for grid array microprocessor connectors. these are roughtl .5mm pins in spring loaded sockets that are 0.7mm in diameter

I removed the lens mount and using an old A series camera side lens mount as a template, drilled the location in my lens base for the A pin, which i pressed in and soldered from the back side

I then used the remaining holes in the camera mount as guides to drill the aperture coding as it should be for the F2 -F16 lens.

WHen I put it on the camera, it worked. By this, I mean, I got F2-F16 as an adjustment range through the camera body, BUT...

the linearity of the aperture lever was a big headache. wide open it was KO, but all other apertures over exposed badly, getting worse until about F11 then getting better at F16.

the reason is that the motion of the lever is just not the same as an A series lens. As a result, I concluded it to be a waste of time.

Note that the reason I wanted to do this was to convert my K mounts to A mounts because myK10D was so bad at metering with K mount lenses compared to the *istD. In the end, the metering was no better with the converted lens, however, you did have the possibility of P-TTL flash with the converted lens.

In the end, I decided that If I wanted to do flash work with a K mount, I would use my *istD which supports both TTL and P-TTL flash, and save my time and lenses from the mod
05-17-2011, 12:08 PM   #4
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