Sigma SA Mount

Started 2 months ago | Discussions thread
xpatUSA
xpatUSA Forum Pro • Posts: 17,893
Re: focusing

danski0224 wrote:

Tom Schum wrote:

Again, this is the camera trying to be "helpful" by changing the aperture for you even if you don't want it to, but the lens is not the culprit here. Most digital cameras can't help it, and can't be set up to just leave that aperture where you want it to be. It's a problem that won't go away!

I would suspect that the lens being wide open has something to do with the AF sensors being used (DSLR).

A native f/2.8 lens will use different parts of the DSLR AF sensor than a native f/4 lens.

How does that work, Dan?

I googled but could find nowhere that says that the image circle diameter is dependent upon the "native" f-number ...

... a link to a formula or a ray diagram would be nice.

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