Sigma 85 1.4 AF

Hi all,

I recently got a Sigma 85 1.4, it works pretty good in One Shot AF as far as I can tell, but on servo... not so much.
It can't track someone walking towards it at walking pace on a 5D3 centre point, in good light.
The (sales) people in the camera shop I bought it from are telling me it's normal for a fast prime to be like that, and it kind of appears to be true, with their 85 1.2 giving a similar performance in an unscientific handheld test indoors with not great light, as well as another sigma on a D800.
But the service guy tested it on a tripod outdoors in better light and thinks it's pretty shocking and made the good point that this is what shooting a catwalk essentially is, so it can't be intended performance.

I'm talking between 2 and 4 out of 15 shots being in focus in this test outdoors. Somehow indoors both the 85 1.2 and sigma gave about 6-7 in focus out of 13, although the sales guy was operating the camera for that so he may not have used the same procedure as me.

What do you think?

At f1.4 on FF? Hmm, hard to tell. I think the 50% hit rate would not be way out of line with such a shallow DOF. Holding the focus point on the same spot after focus is achieved seems to help quite a bit, but this is definitely no 70-200L - of course that would be at 2.8 (or smaller) which would/should also significantly increase the hit rate.

How far out are the misses? If it's all over the place with the odd lucky shot, that doesn't sound too good. But if I was trying to track a moving subject I would stop down for sure and still not expect more than 50-80%, but then that's with the 5DII (center point).

ejenner wrote in post #15007173
At f1.4 on FF? Hmm, hard to tell. I think the 50% hit rate would not be way out of line with such a shallow DOF. Holding the focus point on the same spot after focus is achieved seems to help quite a bit, but this is definitely no 70-200L - of course that would be at 2.8 (or smaller) which would/should also significantly increase the hit rate.

How far out are the misses? If it's all over the place with the odd lucky shot, that doesn't sound too good. But if I was trying to track a moving subject I would stop down for sure and still not expect more than 50-80%, but then that's with the 5DII (center point).

Sorry I forgot to mention this is all at f2.8. Some are kinda close but definitely not sharp, others are way off, with a few in focus shots spread around...

All of my tests (no comparison to the 85L was done my way though) was on tripod, with the centre point on the person walking to me's face in continuous burst..

50-80% would be alright for me, this more seems to be 10-50% though... which makes the lens near useless for moving subjects...

I can tell you that from my experience the Sigma doesn't have the best AF but it shouldn't be that bad, I had 2 copies of this lens before the one I have now, one of them couldn't even lock on focus and the other one was just inconsistent, so you might want to either exchange it, if still possible, or send it in to Sigma

eyalha wrote in post #15007288
I can tell you that from my experience the Sigma doesn't have the best AF but it shouldn't be that bad, I had 2 copies of this lens before the one I have now, one of them couldn't even lock on focus and the other one was just inconsistent, so you might want to either exchange it, if still possible, or send it in to Sigma

Yeah, that's what I'm thinking. The service guy seemed helpful and said he's going to talk to the Sigma rep, but the salespeople were rather unhelpful not offering exchange or anything.

Do you have any idea if Sigma might do a test for moving subjects when calibrating/repairing a lens?

To be honest I wouldn't know the first thing about the way Sigma is calibrating the lenses, but from what I hear the usually do a pretty good job.
The way I see it sending it to Sigma couldn't hurt, and would also let you know that you copy is good and then you can decide yourself if it's good enough for your needs