Keith,


Thank you for the reply. It seems like I'm coming up with that same data empirically. As I originally posted, I am at 24mm on my 17-40 when I get the framing I think I want with my 40D. It sort of makes me think I should get the 24mm f/1.4, because I know it is a terrific lens and very sharp, with a very shallow minimum DOF. OTOH, I am kind of scared to get a prime, because it isn't as flexible, but it certainly seems like a 24mm would be exactly what I need in this case. Of course, as composition changes, I'd like the option of re-framing without changing lenses, so that puts me back onto the 24-70. If I had unlimited funds, I'd get both, but I need to be careful until I start bringing in income from this.