I'm shortly going to upgrade from a compact P&S (Canon S40) to a Canon DSLR\nand have been pondering lenses. I find a lot of lenses which have a fixed\naperture, such as the well regarded 17-40mm f4 L lens. I'd have thought\nthat fixed aperture would be a bad thing...\n\nOne of the things about a compact camera is that changing aperture from one\nend of the range (f2.8 for the S40) to the other (f8 for the S40) really\ndoesn't do a great deal in many cases. I was rather looking forward to\nworking, experimenting and learning with a system that allows a good range\nof aperture adjustment. But now, in my quest for a small number (like 1 or\n2) of quality lenses as a starting point, I find myself homing in on lenses\nwith fixed aperture.\n\nAm I right to be concerned about this, or is having a single wide lens fixed\nat f4 a good thing for reasons I don't understand?