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Message: <blockquote data-quote="David Ellsworth" data-source="post: 1865450" data-attributes="member: 40206">Wow, cool shot! I hadn't seen Osprey nestlings before, and didn't know they had red eyes!Could you please show a 100% crop so I can see how well the 400mm DO is holding up under this magnification?I could be wrong but judging from the reduced picture, it looks like there was some front-focus... the wood looks sharper than the nestlings. So if that really is sharper, you could just show a 100% crop of part of the wood that poop stains on it...That diffraction index only tells you when diffraction softness begins. But this effect is very subtle at first! It's not until about 1.3x that aperture that the softness will start being really noticeable, and that's only on a lens as sharp as the 100mm USM Macro. On a lens like the 100-400mm, which is still sharp but not as sharp as the Macro, I've found that it doesn't start to get much softer than normal until 1.6x or 1.7x that aperture or so.I don't have a 7D, but going by that scale, the diffraction index on the 450D would be f/8.2. That agrees pretty well with tests I've done with an artificial star... but this is a very artificial test, and most subjects don't have as much contrast as a pinpoint star against a black background. Tests I've done on my 450D show that my 100mm USM Macro doesn't get really noticeable softer until f/11, and my 100-400mm doesn't get really significantly softer until f/14 or so. Note that I'm a pixel-peeper (I got a 2560x1600 LCD so I could better indulge my pixel-peeping).</blockquote>

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