how does A99 calc exposure with a manual lens?

Started Feb 16, 2013 | Discussions thread
Promit Senior Member • Posts: 2,007
Re: how does A99 calc exposure with a manual lens?

William Porter wrote:

My question (by the way) was simply about how the live display works when the camera doesn't control the lens aperture. I wasn't asking about how the camera calculates exposure settings (it's NOT calculating, I'm in M mode so I'm doing the calculating) nor about what happens when I click the shutter (which I understand).

And the answer is basically as simple as you could hope for: there's a video feed with a known electronic shutter time and known ISO. Measure the actual video frames periodically against a desired metering algorithm, decide that the image is too bright or dark, and adjust the ISO or shutter until it's where you want it. Aperture isn't needed for the computation, because everything happens off the sensor stream.

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