Canon 750D - unreliable phase AF

Mr Kaja wrote:

Hi all, I'm forcing a problem with my 750D AF. Contrast AF in liveview works OK, but phase AF is unrealible. Sometimes, it works ok, but sometimes, pictures are soft or even totaly out of focus. Same settings, lens... and I see no connection. It just has better or worse days.

Do you have similar experiences? Would you consider to do nothing/try to repair-replace parts/buy 250D or 850D/buy M6II with reduction (good contrast AF)? Thank you

Before I assume that your lenses are not calibrated correctly with the camera body (i.e. Need micro focus adjustment, which the 750D doesn't have), what AF mode are you using?

Mr Kaja wrote:

Thank you for answer, but no, lenses are not the problem. How I said - sometimes AF works OK, sometimes not. In case of non-calibrated lens, results would be still +- the same (in same focal length). Even landscapes with the same settings can make huge differences.

I know the lenses are not the issue.  I am wondering if its the lens+camera body that's the issue.  This problem is precisely why the more expensive DSLR's have micro focus adjustments.  But before I say buy a better camera, I wanted to know what focus mode you were using, as that also affects AF performance but you have not answered that question yet.

Mr Kaja wrote:

Hi all, I'm forcing a problem with my 750D AF. Contrast AF in liveview works OK, but phase AF is unrealible. Sometimes, it works ok, but sometimes, pictures are soft or even totaly out of focus. Same settings, lens... and I see no connection. It just has better or worse days.

Do you have similar experiences? Would you consider to do nothing/try to repair-replace parts/buy 250D or 850D/buy M6II with reduction (good contrast AF)? Thank you

All of my Rebels was/is like that with certain lenses (I had/have EF 50mm F1.8, EF50mm F1.8, EFS 18-55mm STM, EFS 18-135mm, EF 28-135mm).

Send the Camera and the lens to Canon and ask them to calibrate it. Or better yet, buy a camera with MFA or buy mirrorless instead.

Mr Kaja wrote:

Problem identified - my 750D has really unreliable zone AF. Even new firmware changed nothing. Anyway - middle AF point (only) works on 99% OK and pictures are reasonably sharp.

I don't know what to think about it...

Zone AF will normally focus on the nearest thing to it as it has no idea what your  intended subject is. With a single AF point it should focus on whatever the focus point is covering so you get to make that choice. Given that you got 99% hit rate with single AF point it seems that your camera is working as intended.