Why did I get the Nikkor? Well, it was relatively cheap. I bought this on ebay from a UK seller that sold it as "used" but actually, it looks like a Hong Kong import (yellow warranty card has the "Nikon Hong Kong" print on it). There's NO usage sign on the lens (you'd normally see it on the lens mount or the hood mount). I paid 600€ for this lens and its most likely not only "like new", but really "new" - how great is that?!? It came in a blue/silver box instead of the typical golden boxes that Nikon uses here in Europe
There were other considations besides the price, of course. The zoom range overlaps nicely with my 18-200 superzoom. 24mm is "close to normal" on an APS-C sized sensor and the Nikkor is an excellent performer at 24mm. The instant manual focus override is something I've learned to like from the superzoom already.
Now, the Tokina 12-24/4 is almost the same as this lens, and its "only" 150€ less when you buy it new, so this was almost a "no brain" decision: I wouldn't have wanted to ask myself if I shouldn't have grabbed the opportunity to get the original instead of the third party lens. Besides that, the Tokina has more lens elements and the manual focus override is not as nicely done as on the Nikkor.
Then there's the relatively new Tokina 11-16/2.8 - very tempting because its faster. But does it really matter? At these focal lengths, you can hand-hold a lot of shots safely (that leaves the creative component of being wide open, but its very unlikely that you'll get a nicely rendered bokeh at these focal lengths and distance to focus). And the zoom range of this lens... well, 11-16mm... I didn't find it very useful.
And the third challenger was the Sigma 10-20/4-5.6 - actually, this would've been my choice if I hadn't found the Nikkor. 10mm compared to 12mm really DOES make a difference, and its a great lens, too. On the "long" end 20mm is not as good as 24mm, but still a lot more useful than the 11-16mm of the new Tokina. Actually, my expectations towards the wide end were really high, and the fact that the Sigma goes as wide as 10mm still bothers me a little bit at the moment (I think I'll get over it once I got used to the Nikkor:-).
And finally... in a perfect world, we'd have something like a 10-30mm wide angle zoom. That would be one hell of a useful zoom range on APS-C!
The result is that only a portion of the lenses image circle is used, you're seeing a crop of the image. The difference is expressed as the "crop factor", for the Nikon's its 1.5x (and for Canon its either 1.3x or 1.6x, and the 4/3 cameras have a crop factor of 2x). Lenses are marked with the focal length for full frame (and actually, the focal length doesn't change, just the field of view - the german word "Brennweitenverlängerung" is a very unlucky translation of "crop factor"). When you multiply the focal length on your lens with the crop factor you get the corresponding field of view when you use the lens with a smaller sensor.
A lens with a focal length of 50mm ("normal" lens on FF) has the same field of view as a 75mm ("mild tele") lens on Nikon's smaller sensor. So far, nothing new. :-)
Lens manufacturers have reacted on this and produce lenses for the reduced image circle of APS-C sized sensors. Nikon calls them "DX" lenses, Canon "EF-S". Third party lens manufacturers use similar indications for their lenses. If you look at the line-up of these lenses when you compare them, calculate the corresponding focal length's field of view on FF. Nikon's "classic" kit lens, the 18-70 DX, has a field of view of 27-105mm, which used to be a VERY common focal length range for zoom lenses. The "classic" wide-angle zoom 17-35mm is kinda "reborn" in form of the 12-24mm DX lenses. Nikon's 24-120VR lens has a DX companion now, the 16-85VR. Sigma's 10-20mm is the APS-C companion of the 15-30mm lens. And so on, and so on.
I think its important to remember that. Whats even more important is depth of field and the crop factor. I'll post my findings about that in the next post.