My sigma 50mm (sigmalux) was focusing randomly in the past few months until I decided to bring it at sigma center. What the tech did first was calibration. He made me tried the lens again but performed worst than it was before. I showed him the results and so he took the lens again and brought it inside their working area. After an hour, he showed up and told me that the rear element got loose a bit and some grease soaked a sensor (pointing at the focusing ring and don't know what he was talking about ) which caused the lens to focus randomly. So he made me test the lens again and I was happy with the results. I tested it with subjects ranging a distance from 10 feet to infinity. The results were spot on, mfa disabled. The downside is, I didn't clicked on a subject closer than 10 feet due to my overwhelmed feelings. When I got home, I took some shots (this time ranging from 3 feet to at least 8ft.) and found it front focusing consistently on the same focal plane. Mfa'd it and got +15, for near subjects and no mfa for far objects. The lens is consistent this time and its easier to use but its kind of annoying of getting inside the menu to change mfas all the time.
Did the tech did something wrong? I am currently thinking if the lens could be adjusted again by sigma to make it more accurate at all distances, is this possible? What I dont understand is, why was he able to make it accurate for long distances and not in short distances?
Just to make it clear guys, I am not in despair with the result of the repair. Just wanted answers to my questions. I can get around with the mfa annoyance but it would be better working with one mfa value only. Regards!!!