Canon EF 17-40mm f/4L Test for Sharpness in Images
Comparisons at 20mm with EF 20mm f/2.8 and with Sigma 20mm f/1.8 EX

Also, 20mm equivalent taken with EOS 20D and EF-S 10-22mm lens

Images were taken on the same day at f/11 aperture priority and at ISO 100 in RAW mode and automatic white balance. RAW files were converted to 300 dpi tifs with Capture One Pro v. 3.6. The tifs were enlarged in Photoshop 7 to 20 inch wide tifs, sampled and samples converted to 72 dpi jpg's. Sharpening and unsharp mask was used to optimize image sharpness.

Note: Test photos taken during variably breezy morning. Don't pay too much attention to leaves and and very light foliage that is moving in the breeze.

20mm or Equivalent

Camera / Lens Full Frame - 20mm or 20mm equivalent Crop 1 - Left Edge Crop 2 - Right Edge Crop 3 - Center
EF 17-40mm f/4 @ 21mm
& f/11
EF 20mm f/2.8
@ f/11
Sigma 20mm f/1.8
@ f/11
EF-S 10-22mm
@ 12mm f/11

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© 2005, William L. Castleman