Devilry with an old Minolta lens…

I modified the mount of an old (but very sharp and clear) Minolta Rokkor-PF 1:1.7 f=55mm lens for use with the K10D.

The Minolta lens focusing is done by moving the whole optic´s (5 glasses) front and back in a 11 mm travel for the complete focusing range (from minimal focus distance; 40 cm to infinite).

All the physical distances (lens body-film/CCD plane) stands equal in both cameras (after the lens modification).

The results using the modified Minolta lens in the K10D are confusing. The new minimal focus distance is now 30cm (minimal focusing stop) and the maximum in-focus target distance (at infinite stop) is no more than 1 meter and 10 cm away from the camera. The vision angle is just 20º (before was 46º). The sharpness is like always was; gorgeous!

The question: is any lens (for SLRC) capable to be used in any SLRC (film or digital) independently of the mount problem? I know that digital lenses not always suits in film cameras. Exists other limitation to this?




Two images. Leftmost; stop at infinite. Rightmost; stop at 40 cm. (minimal focus distance). Note the rear lens position in both cases…





The very sharp image at 30 cm!

Thanks in advance for any help.


Best regards.
________________
Dirk TROTTEYN.
K10D+ Sigma 18-50 1:2.8 DC; DA 10-17 fish-eye.
Image counter: 5333.-

If a lens can be made to focus its light on the film/sensor plane then it can be used. A lens is a lens.

What the result will be will depend on the lens design.

This would imply that the lens is too far away from the sensor plane.

Yes, if the lens-to-flim/sensor plane is different in Pentax and Minolta SLRs there will be a discrepancy. This tends to result in closer focusing and no infinity focus.

Thanks John, thanks Stevo,

I understand the problematic more clear now.

Surely my lens stops a little (perhaps 0.5 mm) far away from the sensor plane when focus to infinite. And this is very well comprehended when I see the logarithmical scale in the focusing lens ring. For the closer distances the ring rotation is great, but from 10 meters to infinite the rotation if the ring is minimal (± 2 º no more).

Technically I have the possibility to adjust this difference, so hands at work…

Thanks again my friends. Will comment…


Best regards.
________________
Dirk TROTTEYN.
K10D+ Sigma 18-50 1:2.8 DC; DA 10-17 fish-eye.
Image counter: 5335.-

Well, the distance needed to move the lens for focus at infinite was not so depreciable. I moved the lens 3 mm back (to the sensor) and I need to do a fine adjust, another 0.5 mm, but for do this I need the help of a lathe to get this little distance!

But at least, now I can shot at infinite (without all the fine sharpness the lens is capable) until I do the fine adjusts necessary.





Thanks again John, thanks Stevo for the proffesional help.


Best regards.
________________
Dirk TROTTEYN.
K10D+ Sigma 18-50 1:2.8 DC; DA 10-17 fish-eye.
Image counter: 5378.-