On a DSLR like the D50 where you can up the ISO to 400, 800, or even 1600 with minimal noise, gaining one or two F stops (such as 3.4 to 2.8) is not overly critical. More important is getting a lens with low distortion (key) and fast autofocus (if you primarily use AF). The primary advantage to a larger aperture is that you can use faster shutter speeds, allowing for handheld shots in lower light, but the ISO adjustion serves the same purpose.