About a month ago i decided it was time to get rid of some "uneveness" that i found in my Sigma 70-200 Apo EX HSM.
The trouble was i could focus to infinity at 200mm pointing the AF to a very far point in front of me but when i did that at 70mm it would just end up finding the correct focus somewhere in between 15m and infinity.
I am now going to explain how i solved the problem and then i would like to talk about your experiences.
So, as you might know there are a few metal shims inside the lens mount. Just unscrew the mount itself to reveal them. They have different thicknesses so you can finely adjust the lens to jour body.
So, after a few tweaks i ended up adding a very thin shim made from the bottom of a plastic plate (how cheap is that) . I haven't used cardboard because it was already too thick and could become thicker due to humidity. You have to be very precise when fitting the shims otherwise you could end up with a very tight mount lock because the shim is not evenly pressed inside the mount.
So i tested my lens a bit so i could understand which direction to go and now i have a perfect correspondence between the infinity mark and the actual focus.
I guess everyone should do this with his lenses as we know every camera and glass has its tolerances. The procedure is easier with a prime lens because you have just one focal lenght to adjust. With a zoom lens is like finding the "compromise" or the equilibrium point or rather the exact mounting distance at which every focal lenght focuses accordingly to the distance window.
So, has any of you did the same? Is there anybody that can tell me if this is a right procedure (it was for me) .
