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02-26-2011, 06:29 AM   #1
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Pentax K-x with m42 apaptor

Hi there

I was wondering if someone could shed some light on the situation i have at hand. I have a Pentax K-x and wanted to use some of the old lenses we had kicking around the house. These had M42 screw threads so did some quick research and read that there were M42 Pentax adaptors. To which i bought a metal adaptor but when i screw the lenses in the camera wont take a picture with them fitted.

Can someone please help me!


02-26-2011, 06:34 AM   #2
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Join Date: Dec 2009
Location: Liverpool, NY
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First read page 284 of the manual.

Then read this thread.

A few caveats. You can use a screw-mount lens in AV mode, but it tends to underexpose when stopped down. You need to use up to +2EV. Luckily it is easy to chimp photos with a dslr. In M mode you do not need to use the Green Button to meter. The AV +- button will do that. You can set the Green Button to do something else.

Last edited by boriscleto; 02-26-2011 at 06:39 AM.
02-27-2011, 02:41 AM   #3
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Thankyou very much for your advice.

02-27-2011, 02:50 PM   #4

Join Date: Sep 2007
Location: Bay Village, Ohio USA
Posts: 1,047
Two types of adapters

There are two basic types of adapters, and many brands.

One type, which tends to be the cheapest, has a large-ish flange that sits OUTSIDE the lens mount opening on the camera. This flange prevents the lens from focusing to infinity. This is okay if you're just interested in using the lens for macro work.

The other type, preferred by most knowledgeable users, sits completely INSIDE the lens mount opening. The mount-to-sensor distance is identical for Pentax film and digital slrs. This type of adapter allows infinity focus.

Many prefer the genuine Pentax adapter, which is of the second type. It is a little more expensive, around $30, I believe, but it can be a bit hard to find. Even Pentax is often out of stock.

I have a third-party adapter (a Bower, I think) that has never caused me problems. Some people have reported difficulty removing the third-party adapters from the camera.

Some users, myself included, remove the little spring clip on the adapter that mates with the lens lock mechanism in the camera. With my adapter, at least, friction is more than enough to keep the lens from falling off or even loosening up. I have only one M42 lens that I use on my K10D, a Super-Takumar 50mm, f/1.4. By removing the spring clip and leaving the adapter on the lens, it is effectively converted to a k-mount lens.

If you are going to use M42 lenses on dslrs, a Manual/Auto switch on the lens is extremely useful. Put the lens in Manual mode and you can use Av metering mode on your camera. In this mode, turning the aperture ring actually closes the iris to the selected size. In Auto mode, the iris does not "stop down" to the working aperture until the camera pushes the little silver pin in the lens mount. Unfortunately, dslrs do not have any way to push this pin, so the lens will never stop down. If your lens does not have the A/M switch, you must find a way to modify the lens to force the pin to always be depressed.


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