Focussing issue with Canon 90D and Tamron 24-70

Question

A few weeks ago, I took wedding photos for a friend of a friend. A problem I had been having lately suddenly became very apparent: a lot of photos I take are not in focus. The focus indicators of my viewfinder light up red, so I think I'm focussing correctly. But afterwards, the picture seems out of focus.

Example 1

This is the best example I have of the issue. The couple is standing still and I try to focus on their faces. However, after taking the shot, the focus seems behind them.

Settings: ISO 400, f2.8, 1/160, 52mm

Luckily, there are pictures that are sharp, like this one (same settings):

[ Moderator note: removed for now ]

Example 2

In this example, the couple is walking towards me, so it might be more difficult to focus on them. I used AI Servo focus mode. As you can see, the focus is behind them again.

Settings: ISO 640, f2.8, 1/200, 57mm

Tiles behind the couple seem in focus

Example 3

This example is a little different, as it is very obvious the focus point lies behind the couple. Might be a different issue altogether.

Settings: ISO 400, f4.5, 1/200, 51mm

I shoot with a Canon 90D and a Tamron SP 24-70mm F/2.8 Di VC USD (the older version of this lens).

At first I thought the lens might not be calibrated correctly (backfocus?) but then again, there are pictures that are in focus. I do a lot of video, too, but it seems the problem isn't really there in live view mode. When I do real estate at a high F-stop (8.0 or higher), and in live view mode, the issue is not there. The issue only becomes apparent when shoot stills through the viewfinder.

Does anybody know what could be the issue? Could it be the lens, or the camera itself? Or worse: am I the problem?

Answer 1

You write that the problem is not there when you use live view.

This definitely makes it sound like a calibration problem between your camera and your lens. Live view uses the sensor itself for focusing, while a DSLR viewfinder uses a separate autofocus mechanism which may be off from the actual sensor.

You should look in your camera's documentation how to do that. I found an article on how to do that here: How To Do Autofocus Microadjustment On Your Lens (tutorial). I have not checked how well it works because I don't have your specific camera.