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07-08-2008, 11:51 PM   #1
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An Obscure Lens Compatibility Question

Short question: A K-mount lens should work on a Ka-mount body in aperture priority or manual exposure mode, right?

Longer question: I was home to see my parents this weekend, and I found a stash of old SLRs that haven't been used for over 20 years: a Sears KSX with a K-mount 50mm f/2 and a K-mount 135mm f/2.8, and a Pentax Super Program with a Ka-mount 28mm f/2.8 and a Ka-mount 50mm f/1.7. All nearly mint condition, all apparently never used because almost no one took the time to learn how they worked. The Sears camera (which is built like a tank) was in a diaper bag.

I took the Pentax body, the 28mm, the 50mm f/1.7, and the 135mm f/2.8 body back with me. The camera and the Ka-mount lenses work just fine, and I'm looking forward to shooting with a decent film camera. However, the 135mm doesn't seem to work correctly on the Pentax. The meter massively underexposes (at least 5-6 stops), and it doesn't seem to reflect any changes I make on the aperture dial. Nothing changes when I manually stop the lens down with the depth of field preview lever.

Am I wrong that K-mount lenses should work on the Super Program body, or is it some weird issue with a third-party lens? For reference, it's a Sears 135mm f/2.8, 52mm filter size, built-in lens hood, stops down to f/22, 6-bladed aperture, looks to be multi-coated. I've not had a chance to check the optical quality, but it just sort of feels like a good lens, and I'd like to be able to use it.

07-09-2008, 06:12 AM   #2
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My guess is that the aperture blades may be sticky and not re-opening after closing down.
Does it have a selectable A/M switch? Switch to M and while looking through the lens and see if you can manually open and close the aperture by turning the dial and or pushing the auto pin. Could need a clean after sitting still for all those years. Lots of sites have help if you Google "Cleaning Aperture Blades".
07-09-2008, 06:16 AM   #3
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The 135 is proabably an 'm' type of lense. You will need to go to the allow aperature ring setting in the menu (I'm not sure which menu path) and when you are shooting with it, use the M setting on your dial and press the AE-L button to get correct metering. There are several threads on the forum that go into a lot more detail.
07-09-2008, 07:17 AM   #4
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Folks, the Super Program is an old school film body and there aren't any menus and the 135 is a K mount not a screw so it won't have the Auto/Manual switch either.

To check the aperture blades, hold the lens in front of you and push the pin/lever in the mount that does this. The blades should snap closed pretty fast. But this isn't the most likely problem.

The manual is available from many places on the net, including here:
Pentax Super Program Manual
On the Super Program, you have to go into manual metering rather than auto on anything but the A lenses. This is easy enough, you set the aperture via the lens ring and the shutter speed via the buttons on the body. You'll see the exposure indicators in the viewfinder.

07-09-2008, 07:22 AM   #5
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Nesster has it right and this is actually a very good lens. So as long as the blades move fine and are clean, you should be fine in full manual.
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