Originally posted by ckusnierek I was thinking about a 50mm prime. Actually a 50/1.7, nifty fifty as I have read on the net. All reviews say this is a "must have lens".
50mm lenses used to be must haves, on film cameras, before zooms were invented. They were still one of the first lenses you'd get in addition to a zoom on film, because the focal length was close to "normal" on that format (a complicated subject, but basically, pictures taken at that focal length on film look "normal' when printed at common print sizes and viewed at typical distances for those print sizes.
On digital (APS-C format), 50mm is no longer normal (33mm is), so it's not necessarily still the "must have" it used to be. But since 50mm tend to be the cheapest prime lenses on most systems, it's still a common recommendation. And 50mm is still a potentially useful focal length on APS-C - although for different purposes than it would have been on film.
Rather rely on what someone else tells you is useful to the, use your zoom to tell you what focal lengths are most useful to *you*.
Quote: So my question is what is the advantage of a 50mm prime verses a good 18-55 other than aperture?
Maximum aperture is the big, huge, gigantic advantage. Should be sharper too, but that won't matter in practice nearly as much.
Quote: And why do they not seem to make a zoom with aperture below 4?
Sure they do. Quite a few f/2.8 zooms out there, from Pentax, Tamron, and Sigma, in a variety of different focallength ranges.
Quote: If I go with a 50/1.7? which brand/model
On the assumption that you'd be getting it just because it's the cheapest prime you can get and not because it's actually ll that useful a focal length for you, I'd keep it cheap by going manual focus - the "M" or "A" series 50/1.7. See the many other threads on 50mm lenses in this forum and the lens forum for discussions of the tradeoffs, but basically, "A" lenses give you full autoexposure whereas "M" lenses require "M" exposure mode.