Canon EOS 800D autofocus works in Live View but not through the viewfinder
Asked 4/21/2023
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On a Canon EOS 800D / Rebel T7i, autofocus works normally in Live View, but through the optical viewfinder it will not focus reliably or may not allow a shot. Half-pressing the shutter may cause lens movement, but the viewfinder image still appears unfocused and the resulting photo is also out of focus. What causes AF to work in Live View but fail through the viewfinder, and is there anything to check before sending the camera to Canon service?
Originally by Photography Stack Exchange contributor. Source · Licensed CC BY-SA 4.0
Photography Stack Exchange contributor
3y ago
2 Answers
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In "live view" mode, focusing is done using the main sensor, but when you use the view finder focusing is done using a sensor at the bottom of the camera:
(EOS 450D above, yours could looks a bit different).
You can see it/access it more easily if you lift the mirror up (which is done using the procedure for "manual sensor cleanup"in the camera menus). Check for dirt/obstruction, use a rocket blower if necessary, but make sure you aren't bowing the dirt to the sensor.
Otherwise, Canon service...
Originally by user75947. Source · Licensed CC BY-SA 4.0
user75947
3y ago
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Generated from our catalog & community — verify before relying on it.
Yes—this can happen because the camera uses two different autofocus systems. In Live View, focus is done using the main imaging sensor. Through the viewfinder, focus is done by a separate phase-detect AF sensor and mirror assembly.
If Live View focuses correctly but viewfinder AF does not, the likely issue is with the dedicated viewfinder AF path rather than the lens. Before service, check:
- that autofocus is actually assigned to the shutter half-press and hasn’t been decoupled in the camera settings
- for dirt or an obstruction affecting the viewfinder AF sensor area/mirror box; use a blower carefully if needed
If those checks do not help, the problem is likely mechanical/alignment-related in the AF sensor or mirror box, which generally requires Canon service. In the reported case, Canon fixed it by checking the camera and adjusting/replacing parts related to the image sensor and mirror box assembly.
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AI3y ago
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