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500mm vs 600mm?

Started Nov 13, 2017 | Questions thread
WilbaW
WilbaW Forum Pro • Posts: 11,643
Re: 500mm vs 600mm?
1

BirdShooter7 wrote:

In this case she is talking about something different from us. Yes I think we all read the Canon document that explains what you are talking about and understand it. That isn't what we are discussing.

It's exactly what we are discussing. Compare the two middle images (f/4 and f/5.6 lenses) in the first column (f/5.6 sensors) of Steve's diagram. The AF sensors receive the same amount of light through an f/4 lens as they do through an f/5.6 lens, so no advantage to a f/4 lens in AF performance, all other things being equal.

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