Why does my Canon 50mm f/1.8 STM front/back focus on an EOS 1200D through the viewfinder but not in Live View?
Asked 9/12/2016
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I’m using a Canon EOS 1200D and noticed that my EF 50mm f/1.8 STM often looks soft when I autofocus through the viewfinder. If I switch to Live View autofocus, focus is much more accurate. My other lenses don’t seem to show the same issue.
Since the 1200D doesn’t have AF microadjustment, I’m trying to understand what could cause this to happen with only one lens. Is this likely a body/lens AF calibration mismatch, or could the lens simply be soft at f/1.8? What’s the best way to diagnose and correct it?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
9y ago
2 Answers
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AF alignment is not a camera flaw or a lens flaw — it's a matter of how the two you have work together. Your new 50mm may be perfect out of the box for someone else's camera — and their camera wrong for all of the rest of your lenses.
Since your camera does not have a user-accessible focus adjust feature I suggest sending the camera and lens to Canon for alignment.
Originally by user1943. Source · Licensed CC BY-SA 4.0
user1943
9y ago
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If Live View AF is accurate but viewfinder AF is not, that points to the phase-detect AF system used through the viewfinder, not the imaging sensor itself. A mismatch can show up with only one lens because AF calibration is about how that specific body and lens interact, not necessarily a fault that affects every lens equally.
Also, the EF 50mm f/1.8 is commonly softer wide open at f/1.8, and its shallow depth of field makes even small focusing errors much easier to notice than with slower lenses. So you may be seeing a mix of normal wide-open softness and slight AF misfocus.
What to do:
- First rule out technique issues and test carefully.
- Compare results at f/1.8 versus stopped down (for example, around f/4).
- If Live View is consistently sharp and viewfinder AF consistently misses, the body/lens pair likely needs calibration.
Because the 1200D has no AF microadjustment, the practical fix is to send the camera and lens together to Canon for alignment/calibration.
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