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This is what I get pretty much every time when shooting in Live View mode using the Canon 50 1.8:

Live View shot

This is what I get when I'm lucky when focusing through the viewfinder:

enter image description here

This is what I get when I'm not lucky (20-30% of the time):

enter image description here

What's moderately interesting (and kind of confirms this blog post from LensRentals) is that the kit 18-135 STM has a much higher success rate when focusing using the viewfinder.

Is there anything I can do to improve focus accuracy with the nifty fifty except shooting in Live View mode? I imagine other lenses like Tamron 17-50 2.8 will have similar issues?

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  • \$\begingroup\$ I assume that you are receiving a "focus confirmation" signal in each case, and that these images are the result after you receive it. ? \$\endgroup\$
    – Russell McMahon
    Aug 10, 2012 at 21:40
  • \$\begingroup\$ yes. they were all taken using a tripod, with a remote release cable and with mirror lock-up. \$\endgroup\$
    – Baczek
    Aug 10, 2012 at 21:43
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    \$\begingroup\$ Well, for one, the 50/1.8 does not have a USM AF motor, so its accuracy is wanting to start with. Combine the very low-grade AF motor in the 50/1.8 with an extremely thin DOF and what appears to be relatively low light and the lower precision of the dedicated phase-detection AF sensor, and your going to have a miss rate quite a bit larger than zero. The benefit of using live view here is that phase-detection is used to "get close", and contrast-detection is used to "finalize". Its actually the CD-AF in live view that is giving you the superb results...not the FPPD-AF. \$\endgroup\$
    – jrista
    Aug 11, 2012 at 0:20
  • \$\begingroup\$ @jrista: Yeah, it wasn't sunlight, but it wasn't dark either. If I understand correctly, I need new lenses if I want to use a body with PDAF, or I can pretend I have a mirrorless and shoot with Live View. Correct? \$\endgroup\$
    – Baczek
    Aug 11, 2012 at 7:00

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You don't have a body with AFMA (auto-focus micro-adjust), but there's the possibility of sending body and lens to Canon for calibration, that should get the phase-detect AF to work as good as it can with that lens.

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  • \$\begingroup\$ Didn't try it but I'm going to accept anyway. Sounds sensible. When I get around to actually doing it, I'll try to remember to update this question. \$\endgroup\$
    – Baczek
    Sep 24, 2012 at 12:43

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