I shoot film stills where flash is also a big no-no...
You would be surprised how dark some scenes are and can be a struggle using auto focus. I find the reflection on an eye is light enough to trigger the autofocus.. I shoot up to 6400 ISO and try not to shoot below 1/100th for sharpness. All on a 5d mk111. Depending on the lens, you can loose some sharpness shooting wide open. I have had some success with the new Sigma Art Series. They trounce the L-series Canon for sharpness (@1.4). I have both 35mm 1.4f and 50mm 1.4f. I still love my 70-200mm 2.8f Canon though
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