Canon 90D with Tamron 24-70mm f/2.8 is back-focusing through the viewfinder
Asked 3/1/2022
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My Canon 90D with a Tamron SP 24-70mm f/2.8 Di VC USD often produces images that look focused behind the subject when I shoot stills through the optical viewfinder, especially at f/2.8. The AF point confirms focus, but reviewing the images shows back-focus. In Live View and video, focus seems accurate, and stopped-down shots are less problematic. Does this suggest a lens/body calibration issue, and is autofocus microadjustment the right fix?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
4y ago
2 Answers
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.
Originally by user96847. Source · Licensed CC BY-SA 4.0
user96847
3y ago
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Generated from our catalog & community — verify before relying on it.
Yes — this strongly suggests a phase-detect autofocus calibration issue between the camera body and lens, rather than simple user error. On a DSLR like the 90D, autofocus through the optical viewfinder uses a separate AF system, while Live View focuses using the imaging sensor itself. If Live View is accurate but viewfinder shots consistently focus behind the subject, that points to back-focus in the viewfinder AF system/lens combination.
The fact that it’s most obvious at f/2.8 also fits: the shallow depth of field makes small focus errors much easier to see. At f/8 or higher, more depth of field can hide the problem.
The usual fix is autofocus microadjustment (AFMA) for that lens on your camera. Check the 90D manual for how to apply lens-specific AF microadjustment and test carefully at a suitable distance. If you can’t correct it adequately with AFMA, the lens and/or camera may need service calibration.
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