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Bhogi · Guest

My new Sigma 50-150 f2.8 has about 4cm of front focus. I purchased it
nevertheless because the lens can be calibrated.
What seems strange to me is when I focus it manualy using central
focus point on my Canon 20d, the focus is also confirmed about 4cm in
front. It's fair to say I don't know what I'm talking about, but I'd
realy expect when focusing manualy, there should be no lens focusing
logic involved for focus confirmation, only camera sensors.

In the viewfinder the confirmed point of focus is visualy less sharp
than 4cm in front at the distance of around 1m.

My only other fast lens is 50 1.8 which focuses sometimes in front
sometimes behind, which is to be expected from a cheap lens, but I
never noticed any focus problems at all.
I also tested the camera with my 500mm f5.6 mirror lens, which has
zero DOF at short distances, thinking if I could focus it acurately
using the viefinder, there's nothing wrong with my camera. The focus
was dead on.

Does this sound like the camera also needs calibration, or the lens
only? Sigmas are known for their front focus problem.
Otherwise the lens is great when focused in the distance but I'll use
it primarily for portraits and shallow DOF, for that it's useless the
way it is now.

Thanks in advance.