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| Re: 5DM3 front focusing in low light |
Was shooting with my week-old 5DM3+50mm f/1.4 today and noticed alot of OOF shots in low-light, even after having AF tuned my lens to -1 with lens align the day I got the body. Put the camera back on my lens align station and found that its focus is still perfect at -1 in EV 8 lighting (f/1.4 1/160 ISO 100) but it front-focuses in EV 4-5 lighting (f/1.4 1/13 ISO 100). I then tried it with my 50L and saw the same thing. Has anyone seen this?
Here are my 50 f/1.4 images. In these images the EV 8 lighting is 5000k LED (top images), whereas the EV 4 lighting is tungsten (bottom)...although I've tried EV 4 with the LED with the same front-focused results.
AF firmware does not have good AF sensor(s) reading...so it fails & jumps to its exception handling routine which might have some guessing or preset logic to complete its algorithm. It is a normal design for any AF system. This explains why it won't fail with any speedlite focusing light on.