There aren't big difference between old and new versions:
- MK2 9 blade diaphragm, MK1 have 8
- MK2 18 elements in 13 gropus, MK1 16 in 13.
- MK2 82mm filter, MK1 77mm
- MK2 Inner focusing with USM, MK1 front focusing method
- MK2 805g, MK1 950g
So is $1000 worth to cover those changes
Umm and what about the fact that the MTF charts for the Mk2 totally, utterly blow the Mk1 out of the water? The MTF charts look even better than the Canon 24 1.4 II prime! Of course the real test will be in the real world but it appears as if it may be the sharpest non-esoteric zoom ever made.
This looks to be the standard zoom that may finally deliver on high-density sensor FF like the 5D2/1Ds3/5D3. Pricey, but the MTF charts look so insanely good, it's probably worth it. A few people tried them at shows and said that f/2.8 there was no hint of purple-fringing on specular highlights and it look crazy sharp.