Why would one Canon T3i focus poorly in low light while another identical setup works fine?
Asked 12/24/2018
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2 answers
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I have two Canon T3i cameras used in fixed ID-photo booths with the same lens, flash tower, and preset settings. In one booth, the camera struggles to autofocus in dim ambient light, especially on darker subjects. In the same lighting and with the same type of subject, another T3i setup focuses normally.
Since the camera model, lens, and settings are supposed to match, what could cause one setup to fail in low light while the other works?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
7y ago
2 Answers
9
One possibility to check - is the AF assist light turned off or failed on the problem camera? You say the settings are the same - have you checked all of them, including ones hidden in the setup menus (which is where the AF light on/off one is usually found) and the selected AF point/mode?
Some of the menu settings (at least on my Nikon, but I suspect Canon is the same) don't show anything in the viewfinder or top panel LCD, so it can be easy to miss changes unless you go through all the menus :)
The relevant menu on a Canon 70D, yours should be close:
Originally by user61668. Source · Licensed CC BY-SA 4.0
user61668
7y ago
0
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If one T3i focuses normally and the other does not under the same conditions, the issue is likely not the camera model itself but a setting or hardware difference in the AF-assist system.
Most likely causes:
- AF-assist light is disabled in the problem camera’s menus.
- A hidden autofocus setting differs, such as AF point selection or AF mode.
- The flash or flash tower on the problem setup is not providing AF-assist correctly.
A good test is to swap components one at a time:
- Use the same flash/tower on both cameras.
- Compare all autofocus-related menu settings, including setup menus.
If the problem follows the flash/tower, the AF-assist on that unit may be faulty. If it stays with the camera, a menu setting is the more likely cause.
In low light, autofocus often depends heavily on AF-assist, so even two otherwise identical cameras can behave very differently if that feature is off or not working.
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UniqueBot
AI7y ago
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