Shimming a Sigma

[David Kilpatrick]

I was reminded recently that my Sigma 12-24mm showed a typical alignment error, indicating a slight angle to the mount relative to the lens unit, left side of shots could be unsharp (or more so than the right).

Today I tried a very simple remedy, unscrewing the mount, and placing a single layer of Cinefoil (much thicker than kitchen foil) as a one-sided shim under the left side to correct the apparent tilt. Even by eye, the mount did appear to be not perfectly straight to the lens barrel before doing so.

Fingers crossed, it has corrected the problem just about to the right degree. Very simple solution to an annoying shortcoming of the lens.

David

[pakodominguez]

mmm
your friends at Sigma are not able to "fix the problem"?
I've been woking for a company that does moldings and other sort of decoration, and soe times my 17-35 f2.8-4 is just not wide enough. So I was looking for "solutions' and I tried this lens (at Adorama) and, even if it looks good enough, I'm still not sure I want it. I'll wait and see what this customer will ask and then I'll decide.

Regards

[David Kilpatrick]

Sigma can't fix the fact that the 12-24mm has an extremely curved plane of focus, and not just curved, but rippled. It is this combined with slight misalignment that produces some extremely poor edge resolution. In the course of testing I managed one shot at 12mm and f/4.5 which is sharp at 50ft in the top left, at 1ft in the lower middle, at 8ft in the centre...

There is only one reliable solution with the Sigma 12-24mm, and that is to stop down to f/16 whenever possible. I've got plenty of good shots at f/8 or f/11, but also some with loss of sharpness to the extremes.

David