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**Lenses / Re: Quick Comparison: Canon's new 400mm Options**

« **on:**December 19, 2014, 10:28:32 PM »

It's late, and I'm tired, so I don't entirely trust my results here. However, if I'm right, this will explain these results.

The theoretical maximums, simply caused by diffraction, are 1555 lp/ph for f/5.6 and 2199 lp/ph for f/4.

So, the reason the 100-400L improved less is that there's less room to improve between the old one and the diffraction limit than there was for the old 400/4DO which has a higher diffraction limit due to its faster f-stop.

In fact, the result for the 100-400L II is just 1% less than what I'd calculate from a perfect f/5.6 lens behind an AA filter. And that 1% number is based on a rule-of-thumb for the AA filter that itself is less accurate than 1%.

The theoretical maximums, simply caused by diffraction, are 1555 lp/ph for f/5.6 and 2199 lp/ph for f/4.

So, the reason the 100-400L improved less is that there's less room to improve between the old one and the diffraction limit than there was for the old 400/4DO which has a higher diffraction limit due to its faster f-stop.

In fact, the result for the 100-400L II is just 1% less than what I'd calculate from a perfect f/5.6 lens behind an AA filter. And that 1% number is based on a rule-of-thumb for the AA filter that itself is less accurate than 1%.