Originally posted by causey Two questions for users of the genuine Pentax converter: a) how does it behave in Av mode? b) does it allow focus to infinity?
Thank you!
I have a third-party adapter that is similar to the genuine Pentax version. The only difference is that some report that the genuine article is easier to install and remove from the camera. However, I have had no problems with mine. There is a small spring clip on mine (or was, anyway), that is also on the genuine Pentax. This locks the adapter into place, since the screw-mount lenses have no hole for the lens lock pin. I removed the clip. Now, I simply screw the adapter onto the lens and use the lens as if it were a k-mount lens.
I use an old (but still great) Super Takumar 50mm, f/1.4 prime lens on my K10D. I usually use Av mode and it seems to work fine. I set the lens in manual mode and the camera in Av. Then I just adjust the aperture and let the camera pick the shutter speed. I learned on a Spotmatic (that's where I got the 50), so stop-down metering doesn't bother me in the least.
Yes, it allows infinity focus. The genuine Pentax adapter and the better third-party ones all fit entirely within the k-mount opening of the camera, leaving a flush mounting surface for the lens. The cheap adapters have a large flange that extends beyond the camera opening. This adds a mm or two to the camera thickness, which is what prevents infinity focus.
BTW, some non-Pentax screw-mount lenses do not have an auto/manual aperture switch. Since Pentax dslrs have no mechanism to operate the aperture of an M42 lens, this means that such lenses can only be used wide-open. If possible, try to avoid these lenses. Use only Pentax brand lenses or third-party lenses that have the A/M switch. Some have super-glued or jammed the aperture pin so that the aperture is always stopped down, but I've never tried that.