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cppguy wrote:
Cropping into an image or video alone cannot make it darker, everything else being equal. Maybe you're changing the frame rate, which changes the shutter speed. Something else changes. No matter how much you crop, the overall exposure remains the same. Half the image size requires half the amount of light. An f/1.4 lens gives the same general exposure in medium format as in a tiny phone camera. Not to mention cropping in Photoshop doesn't change the exposure, either.
If you use auto exposure, and you crop in to something bright, the automatic metering system might make that area darker to compensate. That's a metering issue. Yes, cropping can affect automatic metering. But if you're in fully manual mode, and you simply crop in, and don't change anything else, the exposure cannot change. Now if your light is flickering, and your shutter speed is very short, you may randomly get a different result, depending on whether you catch a dark phase or a light one. It's like a rotor moving in front of you -- it may or may not block your view at the moment, depending on its current position.
I'm not sure what your camera does, but if it just crop a part of the image, its exposure is unaffected....Show more →
I tried it again today, in video, exposed for 0.0, cropped to S35, got -0.7EV.
Studio lighting, so no ambient fluctuations.
Back to FF, 0.0, crop, -0.7
I'm not super savvy with the technicalities, but cropping on our 7R's with real world scenes results in a lower exposure everytime. My boss puts it down to less light funneling its way to the sensor, as do I.
If I'm wrong I'd be happy and interested to hear an explanation of what is happening.
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