Originally posted by Douglas_of_Sweden Thanks Jim for taking your time to answer my questions.
Why is this lens a preset lens when no other (?) K generation lenses are? Isn't preset aperture a feature found among older Takumar lenses? Where there a previous m42 version of this lens which they just put a K bayonet on?
I think that it has to be a preset design because the shift mechanism would interfere with the aperture readout lever, which is very sensitive to position for accuracy, and the aperture stopdown lever. If the lens were shifted I don't think mechanical linkages would function properly. Of course, in a modern electronic mount design such as Canon uses this would not be a problem.
In any event, I think that stopdown metering would be necessary anyway because of the light falloff at the edges of the large image circle. Even so, I found that images metered at full shift required extra exposure from what the center-weighted TTL metering of my *ist-D suggested.
As far as I know, Pentax did not offer this lens (or any other shift lens design) in M42 mount - it is an original design. Since it was a preset design, there was no need to update it as the later versions of the K-mount lenses were developed. Boz's site indicates that it was still being made as late as 2004.
Quote: My reason for asking about the positions of shift mechanism in relation to iris and lens is a crazy idea that I might try converting an ordinary lens into a shift lens, just because these Pentax shift lenses are so awfully rare. The shift mechanism itself is not so complicated a construction. But it is just a wild idea.
Sounds possible, but as others have said, I think that you would need to use a MF lens to get a sufficiently large image circle to accommodate a significant amount of shift.
Regards, Jim