iGBH wrote:it is considerably more expensive to buy wide angle than something with reasonable zoom. Can anyone explain why this is?
I assume you mean, why is it more expensive to buy a 16mm prime than a 12-24mm zoom? Or are you asking why the 18-200VR is so much cheaper than the 17-55?
Broadly, the answer is that the further you go from the diagonal size focal length, the harder it is to build the lens. For 35mm film, the diagonal is about 50mm, so a 50 or 55mm lens is about as easy as it gets, so you see a lot of good quality, reasonably priced 50mm lenses. With cheap digital SLRs, the smaller sensor is about 30mm diagonally, but only Sigma has really made a prime that matches that size (the 30/1.4, which is excellent value for money).
This also works with zooms, so the full frame 28-70 or 24-70 zooms are typically pretty good, both Nikon and Canon have options in the "stunning, but expensive" range as well as a variety of "great value for the price".
Once you get outside that "easy" range, it starts hurting. Look at the 2x-3x zooms and what they cost - in Canon, a 24-70 is 2k, the 70-200 is 2k but has IS (VR), the 100-400 is only f/5.6 not f/2.8 and it's still 2k. Nikon went for the 200-400/4, but that's stinkingly expensive and only 2x zoom range at f/4.
Again, short lenses work the same way, right down to the UWA crop lenses where you just don't see a fast option at any price - the Nikon 12-24/4 is about as good at it gets. And for image quality in a slow lens, you have a few choices but "cheap" is really not one of them. The kit lenses are short, but... ok, if you know what I mean. Nikon not as bad as Canon in that respect. Both brands offer a pricey 17-55 with stabilisation, and both of those are f/2.8 and quite nice.
Because UWA is really a recent need (the Canon 16-35 used to be a really specialised lens), there don't really seem to be many choices in the primes. Canon make a 14mm rectalinear and a 15mm fisheye, but that's it - they're f/2.8 and there is nothing else. Sigma have a few options, but again the cheaper, slower option is all you get, and it's not really cheap cheap either. There's no 20/1.4 vs 20/1.8 thing, it's 20/1.8 from Sigma for $1000-ish or Zeiss 21/2.8 Distagon ($US3k and counting second hand, they don't make it any more).