7D PDAF Fails Without Covered Viewfinder

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riknash
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7D PDAF Fails Without Covered Viewfinder
3 months ago

Trying to MFA a lens today on the 7D, I discovered something interesting.  While peering through the viewfinder the tripod mounted camera-lens was focused on a wooden railing without any focus hunting. When the same was attempted without the viewfinder being blocked by my eye, the camera hunted and failed to find proper focus, settling on either infinity or a distance well short of the wooden railing. This occurred both in AI-Servo and One-Shot.  As soon as I covered the rear viewfinder with my thumb, the camera focused correctly.   Apparently the extraneous light entering the viewfinder into the camera, interferes with the PDAF and can make it unstable to focus.

Possibly those wearing eyeglasses would limit how effectively light entering the rear viewfinder would be blocked and therefore how reliable the PDAF would function.

Could MFA results be inconsistent if the viewfinder is not blocked while calibrating the lens?

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Canon EOS 7D Sony Alpha NEX-7 Canon EOS 5D Mark III HTC One
Canon EOS 7D
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