Now, a standard entry-level prime lens that I and many other photographers start with is the plastic Canon 50mm f/1.8. For the price (under $100), the image quality and bokeh (background blur) can't be beat. And it gave me a normal focal length lens (between wide angle and telephoto) on my 35mm film SLR camera. 50mm can be (and is for me) a very good general purpose focal length.
When I bought my first 1.6 crop factor DLSR (the Canon EOS 20D), the 50mm f/1.8 lens went from having the angle of view of a normal lens to that of a 80mm telephoto lens. This isn't necessarily bad if you want a telephoto angle of view; but it *is* bad if you really want normal lens coverage.
The first lens I bought to accommodate the APS-C sensor of the 20D was a Tamron 28-75mm f/2.8 zoom lens. 28mm on the 1.6 crop factor DSLR is about 45mm...slightly wide angle compared to a normal 50mm view. Of course it also gave me the full-frame equivalence of a 120mm at the 75mm end. It was a good lens for me, until my daughter accidentally knocked it off of our kitchen counter and permanently crippled it (I was a little surprised how fragile it was).
I eventually went on to a full-frame Canon 5D DSLR and my 50mm lenses (the f/1.8, f/1.4, and f/1.2...I've owned all of them at some point) went back to being true normal angle of view lenses. However, I still have a 1.6 crop factor Digital Rebel that I like to travel with.
On our family vacation to a New York state park last summer, I brought the Digital Rebel and two lenses: a Canon 24-105mm f/4L and a Canon 35mm f/2. Even though the 24-105 gave me the better range of coverage (full-frame equivalent of about 38 - 168mm), I found myself preferring the 35mm f/2 for a few reasons:
1) It's much more compact (here's a photo of the larger 24-105mm next to the 35mm, both with their hoods on)
2) Significantly larger aperture that allowed shooting at lower ISOs indoors and made it possible to shoot in much less light (e.g., photos of my family next to a campfire lighted only by the fire light)
3) Less worry about losing or damaging the lens since it's much cheaper than the 24-105 zoom
A 35mm lens on a 1.6 crop factor DSLR is equivalent to a 56mm lens on a full-frame DSLR. It's slightly telephoto compared to a true normal lens angle of view, but it's not far off. Canon makes a 28mm f/1.8 that I think I would slightly prefer in terms of angle of view (approximately equivalent to 45mm on a full-frame), but compared to the 35mm f/2, it's: 1) bigger, 2) more expensive (around $420 new compare to $240 for the 35mm), 3) has poorer center sharpness wide open (i.e., at large apertures).
I have found the 35mm f/2 to give me great photos and to focus quickly and accurately, even without a USM autofocus drive motor (it makes a high-pitched whizzing sound when it's focussing because it's not USM; but this doesn't bother me).
I really think the Canon 35mm f/2 is a great lens for anyone who owns a 1.6 crop factor Canon DSLR (includes the Canon EOS 10D - 50D and all the Digital Rebels) and would recommend you try one out if you haven't already!
Michael Grace-Martin is a professional wedding, portrait, event, stock, and fine art photographer based in Upstate New York. He is also the author of this blog. All images and text are (c) Michael Grace-Martin Photography. His main website is: http://www.mgm-photography.com/.