This is a fine portrait lens on par with the famous Canon EF 85mm f/1.8 USM. I decided to go for the 100mm f/2 because I use the 1.3x Canon 1D and liked the extra reach of the 100mm over the 85mm.

If I had to use one word to describe this lens, it would be CONSISTENT! My samples below look like I posted the same picture repeatedly (except for the color shift as noted): from f/2 through f/22 there is almost no perceptible difference in sharpness!

While I would have preferred a little more sharpness at 2.5m, it's nice to have the confidence that I can use this lens wide open without losing sharpness!

I used a Canon 1D (Auto White Balance mode) on a tripod with autofocus and 2 second timer delay to prevent shake. The sharpness parameter was set to 1. The purpose of using the autofocus was to test the consistency of the focusing. Due to errors in focusing consistency, some (one or two) pictures came out of focus (OOF) and were useless for comparing sharpness. Overall, the autofocus reliability was excellent. (Sorry the far field pix are way overexposed -- I had it on spot metering +2/3 EV and forgot to switch to evaluative).

Canon EF 100mm f/2 USM (Near Focus: ~0.9m, Far Focus: ~2.5m)
Near scene	Far scene
f/2.0, Near	f/2.0, Far
f/2.2, Near	f/2.2, Far
f/2.5, Near	f/2.5, Far
f/2.8, Near	f/2.8, Far
f/3.2, Near	f/3.2, Far
f/3.5, Near	f/3.5, Far
f/4.0, Near	f/4.0, Far
f/5.0, Near	f/5.0, Far
f/6.3, Near	f/6.3, Far
f/8.0, Near	f/8.0, Far
f/11, Near	f/11, Far
f/16, Near	f/16, Far
f/22, Near	f/22, Far

Notes

• This lens is a slightly near-sighted one. Sharpness up close is EXCELLENT at all apertures.
• At 2.5m, however, there is softness as all apertures, but it's definetely acceptable even at f/2.
• I still can't explain the color shift from f/3.2 to f/11, but it was on all the near photos.
• The shift is less noticeable in the far field due to overexposure.
• I'll try not using auto white balance next time and see if that fixes it.
  It's really a drastic color shift.