Yeah, and Cannon is too easy to misspell!
Bet I can manually focus a 7D (or a D3 or an a850) just fine without any other screen than the one it comes with. I was also told that it is impossible to manually focus a D200 without something called a 'katzdeli' or 'catsear' or something expensive. Fact is, I can do razor sharp macros without any portion of the feline anatomy.
Les, bionet is describing an entirely different issue.
For macro, you're typically shooting at apertures where the stock screen works OK. The Nikon 60mm and 105mm are f2.8 at infinity, around f4.5 at 1:1, and even smaller on tubes or with TCs. My "baby", the 200mm f4 micro-Nikkor is f4 wide open, and f6.3 at 1:1 (if memory serves). And most of my macros don't involve those lenses being wide open.
The default focusing screen has about a 10 degree scatter, it "sees" a "cone" from the f5.6 part of a lens's exit pupil. (screens aren't very precises, it's a mix of f4, f5.6, f8, and smaller apertures). The AF sensors are the same 10 degrees, and so are the split image screens like a Nikon K3 or the Katz Eye and Haouda. Everything is 10 degrees. It's "friendly" for our slow "kit" zooms.
For the system cameras like F3, F4, F5, Nikon used to make a large number of specialty screens, ground glass screens with 20 degree scatter for fast lenses, as well as split images with a 15 degree spread. Ground glass with 5 degree scatter for slow lenses and telescopes, with or without a 7 degree "slow lens" prism.
Canon still does, right up to the 50D you could get the EF-S screen, with a 20 degree scatter. It's dimmer when you use slow lenses, but when you use fast lenses you can really see the image snap into focus, because it shows you about f2 DOF instead of 4-5.6.
Unfortunately, with fast lenses shot wide open (or nearly so) you need that extra snap. Not only is the DOF so shallow it demands accuracy, but there's a problem caused by spherical aberration that causes the optimal plane of focus to be different on a lens at f4 or 5.6 than it is at f2 or 1.4.
So, unless you've got one of those cool Zeiss f2.0 macro lenses and you're in the habit of shooting it wide open, you're not experiencing the same problems that the OP is.
One way camera makers get around this is by adding extra AF sensors with 20 degree spreads to work with f2.8 or faster lenses. But that only helps AF.
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Rahon Klavanian 1912-2008.
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Ciao! Joseph
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