I am in the middle of another round of lens testing. I did this once before when I got my 20D, wanting to know how my lenses (all designed for film) held up against a digital sensor. My conclusions then—every lens is sharp at f/8, and some lenses are better than others.
There are differences between shooting with the Canon 1Ds Mark II and the Canon 20D. The Mark II is less forgiving. It’s akin to switching from 35mm to medium format—with all that additional film area, there’s more that can go wrong. I have less depth of field and so my focus has to be spot on. The camera is much heavier, and therefore harder to hold still. I’m on a tripod more often. What I wanted to know is, with the increased sensor size, is there an accompanying falloff in sharpness on the edges and in vingnetting?
I have three workhorse lenses for most of my shooting: a 17-35mm f/2.8, a 28-135mm IS f4.5-5.6, and a 70-200mm f/4. I have some primes as well, a fisheye 15mm, two 50mm, an 85mm, and a 400 f/5.6. What I don’t have for the Mark II are lenses designed for a digital camera, like the 10-22mm and the 17-85mm for the 20D. Both those lenses are outstanding performers, and are the sharpest lenses wide open that I own.
Here are the results.
17-35mm f/2.8. For sharpness, this lens is a pretty good performer throughout the range. Between 5.6 and 16 it is a stellar lens. It’s actually a little sharper 17mm at f/5.6 than at 35mm. The issue with this lens, as with all wide angle lenses, is vingnetting. At 2.8 at 17mm, it’s 2 ½ stops darker at the corners. In this regard it’s the worst performing lens I own.
28-135mm IS f/4.5-5.6. This lens is a better performer wide. Center sharpness is great wide open (though edge sharpness is in the toilet). Vingnetting is pretty bad wide open, but stablizes at f/8. At 135mm the sharpness edged into "Excellent" only at f/8.
The 70-200mm f/4 is a lens with great contrast, which can mean more than resolution in the perception of sharpness. Again, it is sharper at the wide end than fully extended, but is a good performer up to f/16. Chromatic abberation and vingnetting are there, but not horrible.
My primes however—these are good lenses. My 85mm f/1.8 is the sharpest lens I own. Iit’s a bit iffy at 1.8 and 2, but by f/5.6 it’s sharp, all the way through f/16. I love this lens.
The other great performer is my 400mm f/5.6. Wide open it’s fantastic, which is great to know about a long lens. It’s sharp even with a 1.4 extender—I couldn’t detect any difference with or without. Its only bad spots are f/22 and f/32, which is to be expected.
There is an area where zooms perform notoriously poorly: chromatic abberation. As a compensation, there are sliders in the Adobe RAW converter to fix the Red/Cyan and the Yellow/Blue channels, and you have to use them. The effect does not change over apertures, fortunately, but it does vary according to focal length on a zoom. The extreme example is my 17-35mm. At 17mm I require a +60 correction in the B/Y slider. At 35mm I need a –25 in the R/C. All the zooms have this problem. My prime stars on the other hand, the 85mm and 400mm, require no correction at all.
The next test: how well does the Image Stablizer work, really? And how fast can I really go on my ISO settings?
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