EOS R8 Back focus issue

[2Artie]

I am shooting a R8 with an EF24-105.  Two shoots are back focused. 

My aperature setting on one indoor shoot was around 5.6 to 7.1 and was using a GODOX flash.

A second shoot was outside with aperature settings of f8-f11 with a studio flash as the light source.  Contrasty light with straw bales behind the people.  The bales are sharper than the people. 

Mutiple focus points are selected and both shoots are of people. 

I have read that it can't happen with a mirrorless camera so I am not sure what I need to be doing to figure this out.  I do have a calibration card which I will use to do some in-studio testing.  

[deebatman316]

Have you tried w/o using the flash to see what happens?

[2Artie]

One shoot was a speedlight and one was a dumb trigger. In my studio testing it made no diff.

[2Artie]

Not at an event.  In my studio testing I could not duplicate it with or without flash. 

[p4pictures]

Yes it can be possible, but it's rare for a mirrorless to back focus as the image sensor is also the AF sensor unlike a DSLR.

What AF settings did you use for the photos, servo AF, people subject detection, whole area AF?

Did the camera LCD/viewfinder look really dark when you framed the shot? The reason I'm asking is that with some studio triggers the camera doesn't get a signal to tell it to switch off display simulation, like it would from a Canon flash, so the frame can look dark and actually the camera will struggle to focus. If the GODOX or studio triggers are not cooperating with the camera this might be part of the problem.

[2Artie]

One shoot was a dumb trigger and one was a speedlight. 

I have simulation turned off. Af was expanded center. I replied with an update but I'm wondering if it was the brighter bg.

[2Artie]

Thanks for ideas.  I did some in-studio testing on a focus testing card.  Naturally I'm not seeing the same issue.  I tested the lens with flash and existing lighting.  I did change focus to spot.  Does this sound plausible? I was shooting with expanded center spot and in both cases my bg was brighter than my subject.  In the back of my mind I've seen the scenario where cameras have back focused on brighter backgrounds.

[Waddizzle]

It’s difficult to give any sort of insightful explanations without seeing a few sample images.  The most you’re going to get are a host of educated guesses. 

So on that note, I pitch in my two cents. Your lens has well known issues with lens creep. This can be a problem when you are using One Shot AF and are not mindful of how you are handling the lens. 

[2Artie]

[2Artie]

These are pulled from larger images.  The outdoor shoot was a lot of kids and I am reluctant to post those.  Based upon what the group has said I am thinking that at one event the bright background was creating an issue and on this one I looked at the focus point and some of the back focus were operator error.  It is not as consistent as I thought so I am wondering if part of the issue is not all the camera.