PSA: Public Service Announcement
MFA: Microfocus Adjustment
(Thanks SkipD )
So I am on my second copy of a Sigma 24-70/2.8 EX HSM and just filled out the form to send this one off to be calibrated for front focusing issues. This one seemed to be much closer, my first copy....there was no hope for.
I could not get it to focus correctly. I recently made a thread asking about if the price difference between the 7D and 60D is worth it. Bottom line, my mind was made up to get the 7D until I got a deal on a 50D that I would have been stupid to turn down. I am still going to get a 7D in the near future but this 50D will satisfy my urge for a while longer.
Anyway that is not the point, the point it I thought the Sigma was front focusing so bad that even setting the 50D's MFA at +20 didn't cure it. After days of messing around I was ready to send this one off until I said to myself, "Self, why not just go take some real world shots at F2.8 instead of the hundreds of shots I've taken of focus sheets and close up stuff in my apartment?"
So I leave the MFA at +20 and go outside. All of my shots are backfocused like crazy! So I set the MFA at 0, head back outside and all of a sudden my F2.8 shots are spot on. They are tack sharp right where I was focusing.
So moral of the story, I learned that not only do I not know how to properly use a focusing sheet but shooting objects that are about only a foot away from the lens isn't the best way to gauge how well the autofocus is working. I cancelled the repair.
So unless you know 100% what the hell you are doing leave MFA alone!