OK folks, here's my problem. I just purchased a Sigma 85mm 1.4 ART lens for use on my 5DMk2. I have only used it a few times, but today I gave it a workout in both an outdoor setting and indoor portrait setting.
In both circumstances I was NOT shooting wide open. The outdoor shots included a Rovelight 600B fill, and I needed about F-3.2 and 1/200 seconds (settings driven by ambient light - no ND and didn't want to mess with HSS). All these shots seemed pretty good.
Next, we went inside where I again used the Rovelight on one side, and a Godox 860 on the other. Again, I did NOT shoot wide open. I shot 1/200 seconds, and F-2.8. (I didn't want too narrow a DoF since these were head shots for a career posting).
When I uploaded the shots, nearly every single head shot was OOF almost to the point of not being usable. One or two shots, perhaps, but 20 shots mostly OOF? I was hand holding, but at 1/200 and using a flash, there is no way I should be getting anywhere near the blur I got.
So I set up a test at home. I hung a towel on the wall, set up two flashes, set the F-stop to 1.4, 1/200, on a rock solid tripod, and a 2 second shutter delay. All this should take out all reasonable variables. On my first shot the towel was WAY OOF. Then I locked the mirror up to do a manual focus. I noticed there was very little light to manually focus, so I used a super bright LED flashlight to do the manual focus. The result was razor sharp image. So I am thinking the lens autofocus (or camera's) is screwed up. So for grins, I did another autofocus shot, but this time I used the same LED flashlight when using the autofocus. Result? Razor sharp image.
So, the lens is not focusing well in lower light, but when I depress the shutter halfway, I get the red square and the "beep" indicating an in-focus condition.
So I guess I'm looking for some thoughts on where to go, what to do. The lens is obviously working well in well lit conditions, but why is it missing in lower light but the camera sending the in-focus "beep"
Sorry for the long post. These two posts are Manual focus first, autofocus with LED light second. Both show overall image on the left and a 100% crop on the right.