“2point8″ refers to a wide-open lens, a lens that allows lots of light through. This past summer, I used a wide-open lens on the street. More often than not. I liked how it isolated subjects and generally made scenes feel more dramatic.
There’s a compositional knife-edge between isolating a subject and a frame that’s crowded with people. For my taste, it’s one or the other; the middleground (kind of crowded, kind of not) is less interesting. It’s harder to see (or know, or realize, or care about) what’s important. (An image will prove me wrong on this point tomorrow, I’m sure.)
Shooting wide-open can be hard to do on the fly, even with a sophisticated autofocus camera. I realized something last weekend, while looking for locations that had a worthwhile combination of interesting light and pedestrian traffic.
A good way to isolate the subject is to photograph them in direct light against a dark background. This is Photo 101, but one thing I didn’t realize is that you can use a much more forgiving f-stop with this scenario. Say 5.6 or 8. The background will still be black, whether it’s in focus or not. The light selects/creates your depth of field in this instance. Handy!
It’s a simple thing, really, akin to using flash. When photographing subjects against deep black backdrops, there’s no need to shoot wide-open, which allows you more time to not be holding the camera to your eye, which can be a smiley good thing.