A different way of looking at the focus breathing of the 70-200mm f/2.8 VRII

Started Feb 3, 2013 | Discussions thread
Samuel Dilworth
Samuel Dilworth Regular Member • Posts: 249
And a better way to look at it…

These fast tele-zoom lenses place an afocal lens (a Donders variable-magnification telescope) in front of a regular photographic lens, and thus behave very differently from ordinary unit-focusing prime lenses.

None of them lose or gain a stop of light at close focus. For the purposes of your question they’re all simply f/2.8 lenses.

Whether zooming or focusing, the size of the diaphragm doesn’t change. (The diaphragm is placed in or near the regular lens behind the afocal lens.) Although the physical diaphragm doesn’t change size, the entrance pupil does change size when the lens zooms, because the magnification of the upstream Donders lens changes. But since the Donders lens is afocal and appropriately sized it doesn’t affect the relative aperture (f-number).

Your Canon EF 135mm f/2L USM has less depth of field than your AF-S NIKKOR 70-200mm f/2.8G ED VR II because it’s one stop faster.

On the acceptance angle of the sensor pixels: even though your Canon EOS 5D is old, it does better than most cameras – and quite possibly better than the Nikon D800 – for incoming light at high angles of incidence. However, this advantage isn’t seen with f/2.8 lenses. DxOMark has more info on this here.

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