The chief virtue of a digital SLR is that it pretty much requires me to adopt that two-handed picture-taking position – one hand supporting the lens, the other firing the shutter – the one that makes women swoon and otherwise-more-handsome men gnash their teeth in envy. (In applying that last sentence to yourself, please adjust for your gender and sexual preference.)

Oh, and even an inexpensive SLR usually kicks the oh-so-tiny derriere of most point-and-shoot cameras.

But there’s another virtue, one that may not have occurred to you if you’ve been enchanted with the zoom lens that almost certainly came with your SLR kit. It is this: you can swap that lens for a much nicer one.

By “nicer”, I don’t mean it has even more zoominess; your first new lens probably won’t have any. In fact, I’m going to recommend that you walk right out and get yourself a fixed-focal-length (a.k.a. “prime” or, as my dad used to say, “taking”) lens. Say, 50mm. Plan to spend between $100 and $150 for it.

In my case, I just picked up Canon’s 50mm lens for my Rebel XTI. (Thanks again, Alex. Mwah!)

What can’t I do with it? Take wide-angle pictures. Crop the photo with a twiddle of thumb and forefinger. Get less than a foot from my subject. These are all things I can do with the 18-55mm zoom lens that came with the camera.

What can I do with the 50mm lens that I couldn’t do with that old lens?

Well, shoot this for starters:

That’s hand-held, baby. See, one thing I’ve learned about lenses is you can have any two of features, quality and low price. And once you add something like zoom capability to a lens, you’re going to have a big tradeoff in quality. (Or a heartfelt discussion with your credit union.)

That’s most noticeable in the aperture – how wide the lens can open to admit light into the camera. The lens that came with the XTI, when it’s zoomed to 50mm, lets in about one-quarter the light of my new lens. (Aperture is measured in “F-numbers”, where lower numbers mean more light – it’s a math thing. My new lens has a maximum aperture of f/1.8; look for something around that number or lower.)

So suddenly, I’m able to take indoor pictures of the kids without resorting to the intrusiveness and harshness of the built-in flash. Streetscapes at night. And the odd bit of Granville Island neon. It can’t work miracles, and I’m still getting used to “zooming with my feet” (i.e. walking backwards or forwards to crop the picture), but this prime lens is changing the way I do photography.

I knew it was going to be improvement. But honestly, the leap from the cheapie zoom to the inexpensive but lovely 50mm feels like the same distance as my SLR was from the point-and-shoot I’d been using.

This, by the way, is in lieu of a new external flash. That advice – to start with a new, quality lens instead of throwing more light at my subjects – came from a number of folks. So thanks to Reilly, Kris, Roland and several other folks at PhotoCamp / MooseCamp / Northern Voice for steering me wisely and well.