Here it is on my 1DS3 - pretty wide on FF. I would say it would be good for indoors etc
Impressions:
1. It isn't silent, but quieter than the 50 f/1.4
2. Quicker and more accurate AF then the 50 f/1.4 - but not fast like, say the 70-200 f/2.8 II
3. It is tiny - in comparison to the 50 f/1.4 the end of the 40 is before the focussing ring of the 50
1DS3 + 40 taken with 1D4 + 50f/1.4
1D4 + 50 taken with 1DS3 + 40