How can a 24-70mm and a 10-22mm both be "wide angle" lenses?

Question

I've been looking at a 10-22mm lens for my Canon T2i. I've also come across some other "wide angle" lenes, like the Sigma 24-70mm F2.8.

I don't understand how a wide angle lens can be such high numbers. The kit lens is 18-55mm, 18 is lower than 24, so does that mean the kit lens is a "wide angle lens?

Also, the 10-22mm lenses are pretty expensive. Around $400 - $800 (and up), depending on the aperture. Any tips for getting a low priced wide angle lens? I was thinking about the Rokinon FE14M (14mm prime) that amazon.com has for $289. Not the "best" lens but it seems to have OK ratings for the price and I thought I could trade up later. Any reasons that is not a good idea?

Answer

Traditionally, lenses wider than 24mm on full-frame are "ultra-wide". On a smaller-sensor Canon DSLR, a 15mm lens provides that same field of view (16mm on Nikon, Pentax, or Sony; 12mm on Olympus/Panasonic). So on an APS-C camera, a 20mm lens would be "wide" but not "ultra-wide" — but with the increased field of view of full frame, that would fall under ultra-wide.

On full frame, a 35mm lens is wide angle (but not ultra-wide); that same lens would be "normal" on an APS-C camera.

In either case, yes, the 18-55mm kit lens is a wide-angle lens. On a crop-factor DSLR, that nicely covers a reasonably wide angle, through normal, up to a moderate "portrait-length" telephoto.

(On some systems, some lenses designed for APS-C cameras won't work at all on full frame. Or, they'll work but with poor performance in the corners — and on Nikon, for example, this is compensated-for by automatically cropping-out the edges when a designed-for-APS-C lens is attached. But it's pretty much universal that full-frame lenses will work on APS-C.)

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