I've been having an issue with a new Sigma 35mm I bought. The first time I sent it to Sigma they did an AF update and it is much more consistant between indoors and out, however it was missing focus quite a bit. So i sent it back to sigma and requested calibration. (on my 5D2)
So I get a phone call from Sigma support and had a nice 10 minute conversation with the tech who is testing the lens. He mentioned that my camera body may be front focusing. (I need between -10MA and -14MA depending on subject distance) What I don't understand is that other lenses I have require no MA and seem very sharp, however they are 2.8 or slower lenses.
Do cameras front or back focus? I was under the impression that the lenses front and back focused. is this something that I would want to have Canon look into the next time I send it in for a clean and check?
On the positive, I have to say that Sigma may be on to something with their new USB dock. He explained how it worked for me. Apparently there are 6 different settings you can change vs just one in camera. So you can set the lens to front focus one amount from say 5' away, set it to front focus a different amount from 15' away, and so on. If a new setting makes it worse, you can just go back to a previous setting. This would also be a godsend for those who sell their used lens. lens plus dock so you can pretty much guarantee it will work and be calibrated with any body.