M42 Lenses on Pentax DSLRs
Surely the answer given to "Tedley" in this month's (May 2011) What Digital Camera by PH (Phil Hall?) is in part wrong. As I understand it, whilst you can use M42 lenses on all Pentax autofocus SLRs, including digital, you will still get metering in Aperture Priority and Manual modes; aperture control is manual, as stated in your answer, but metering is NOT manual. The only thing you must be wary of is whether the lenses have an auto/manual switch; lenses without an auto/manual switch can only be used at full aperture. To my knowledge, there is only one supplier on eBay whose adapter includes the extra ring to depress the aperture pin, though, of course, firms like SRB manufacture rings that can do this.
Was PH thinking of Nikon cameras, where, if there is no electronic contact between the lens and the camera, metering has to be totally manual?
One other point - Pentax screw thread lenses were exceptionally sharp, especially at the centre. Using them on a DSLR with cropped sensor, only the centre of the lens would be used, so results should be very satisfactory.