Shot at approximately 18x focal length, all are extreme lower left corner crops (4% total of target). All lenses shot with the 1DmkIIn, except the 17-50 which was shot using the 20D.
Lenses tested:
Tamron 17-50mm f/2.8
Sigma 20mm f/1.8
Canon 28mm f/1.8
Canon 50mm f/1.8
Sigma 70-200 f/2.8
Canon 85mm f1.8
Canon 135mm f/2
Sigma 180mm f/3.5 macro
Canon 300mm f/4 IS

My impressions:

The 17-50mm f/2.8 shows softness in the extreme corner of these crops. Not surprising, it's in the reviews. It's worst at 17mm, f/2.8. In real world tests this corner softness isn't an issue at all. This lens also suffers from distortions not uncommon for a wide angle and is easily fixable with PTLens or similar apps.

The 20mm f/1.8 appeared soft in the corners in initial testing. After some retesting that takes into account field curvature (this is esp important at close focusing distances), the corners of the 20mm f/1.8 test good wide open! By f/5.6, the corners are excellent. Combined with great center performance, this is a very good lens.

The 28mm f/1.8 is a new lens in my fold, and as such my observations are initial ones from the test and do not reflect the benefits of "real world" shooting. I will say that the USM is great (read: fast!)on this lens and it is small but well balanced even on my large 1DmkIIn. It does focus well in not so good light. Regarding the test results, it is as billed. Which is to say, it is usable in the center at f/1.8 (some loss of contrast here) but is noticably sharper at f/2.2 with better contrast. By f/2.8 it is very sharp with excellent contrast, although the corners still suffer, and at f/5.6 it is excellent in the middle and very good in the corners.

The 50mm f/1.8 tested consistantly accross aperture settings as moderately sharp. A very good performance for an $80 lens on a 1.3x crop sensor.

The Sigma 70-200 f/2.8 tested inconsistantly from aperture to aperture and FL to FL. In general, results were average except at 135mm f/2.8 were they were excellent for some reason. 135mm seems to be a sweet spot for this lens.

The 85mm f/1.8 tests very good from f/1.8 on and was excellent by f/5.6. Very impressive for this class lens.

The 135mm f/2 tests very similarly to the 85mm f/1.8. Impressive, but expected.

The Sigma 180mm f/3.5 macro (non DG) tests very good from wide open onward.

The 300mm f/4 IS tests superbly at all apertures.


If you find these tests helpful, please leave a comment :) .

Ian