Originally posted by Lowell Goudge 
A couple of notes.
What causes the reported "fiddly" behaviour is the fact that the contact pins on some sigma A lenses are drilled in a pair of straight lines of 3 pins, lying tangent on the true circle center of the Pentax mount. This causes minor mis allignment of some pins and lost contact. Rock the lens back and forth in the locked position and see if you can get F2.8
No such luck with wiggling and jiggling my Super-Wide II. It seemed to be more from the contact actually receding into the mount a bit.
Quote: Second, the mini wide II with KA mount suffers very badly from lateral CA. Unless you plan to spend time in PP with every image and correction the edge resolution is pittifull at best
Lightroom 4+ does a pretty good job of getting rid of this with a single checkbox you can leave on as a default, so no time spent. It is nice to see images actually become sharper than the lens actually took them. (Lateral CA is actually mostly corrected/fixed rather than masked.) I can't speak for the extreme (and unseen) edges you'd get on a full-frame camera, but for the lateral CA I do see from certain old lenses (even really bad) on the edges of the APS-C frame, it does a marvelous job of correction and improving resolution.
Ok, see pic below for bit of foil tape covering one contact. No problems whatsoever since -- before that it was a crapshoot what it would read. (Seemed to depend on the ambient temperature.)
Post #6 by scratchpaddy
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