Are all mounts equal?

I for one would be very interested if Pentax offered a retofit service for older lenses. I wonder what a reasonable price would be to make it viable. Anyone care to guess ?

/Ian

George perhaps I used the wrong term in 'fooled'. When I tried this I did replace the base with one taken from a damaged 'A' series lens. Aperture information was shown in the viewfinder, however as I stated the exposure problems remained.

This is my understanding and I may be wrong here

Using a 50mm F1.4 'A' series lens as our example, lets say for our purposes to go from F1.4 to F22 requires the aperture arm to move 16 mm. From the 'A' series onwards Pentax lenses have linear aperture control, therefore if F5.6 is selected the aperture arm will need to move 8mm from its fully open position. For F11 it would be 12mm ect.

Now K or M series lenses were designed with non linear distances between F stops. The amount does seem to vary by lens, so in the above example we might find pretty close correlation at F5.6, but a widening gap from F11 upwards. The result is that as we move from F1.4 to F22 we go from over to underexposure.

Now when we fit the lens to the DSLR, the camera would recognise the modified lens as a 50mm F1.4 'A' series and when asked for F11 would move the aperture arm 12 mm, which in this case would be too much and would result in under exposure.

I hope this helps - regards Steve