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
Regular MemberPosts: 222
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Re: And a better way to look at it…
In reply to MisterHairy, Feb 4, 2013

MisterHairyArse wrote:

I don't think that it remains a constant 2.8 though when it is breathing, as it looks to have less DOF than the Canon 135mm lens at 2.8. Maybe that's because the quoted f stops of many of these lenses benefit from a generous bit of rounding/truncation and are presumably only quoted for infinity focus.

Correct: lenses are almost always a little slower than their claimed maximum aperture (this one might actually be f/2.9, for example).

In addition, the Nikkor at full aperture probably has significantly more vignetting than the Canon stopped down to f/2.8, which would increase off-axis depth of field, possibly by a lot. The reported f-number only applies to the centre of the image.

If the lenses have different field curvature/astigmatism they’ll be hard to compare too, e.g. the background at a particular image height might look more blurred with one lens than the other, because the field of that lens curves inwards at that image height, but does so less or not at all with the other lens. Etc.

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