From an email I sent to a friend. The question at issue revolves around me getting my first digital camera with interchangeable lenses (a Nikon d50). The problem with having a choice of lenses is...needing to make a choice.
I've been thinking about the "how do I know what lenses I need?" question lately...
I was reading online that the conventional wisdom holds that the vast majority of pictures taken with a zoom lens are taken at either the minimum or the maximum focal length. So, I decided to check my own pictures and see if that's true. I found this program online called jhead, which will dump the exposure info out of digital camera JPEG files.I ran my entire iPhoto library through it, and analyzed the results with a Perl script.
I found out some interesting things about my picture taking habits.
Looking at the data for the E-10, which is the camera that I've taken the most pictures with, the distribution of zoom focal lengths look like this. To convert these from the E-10's smaller sensor size to the equivalent for 35mm field of view, you'd need to multiply by about 4.
focal # of pictures
The conventional wisdom is confirmed, I guess. It's kind of fascinating to me that it's as lopsided as it is in favor of wide-angle though. I mean, I suspected that would be the case, but I didn't expect that it'd be so extreme.
It also interesting that there's that peak at 17mm (68mm equiv). Unfortunately, iPhoto won't let me search by focal length, but a quick visual scan through the library shows that most of these are relatively close-up shots of people's faces.
So based on the data, what *I* really need is one wide angle zoom lens, one portrait taking lens, which can probably be a non-zoom lens, and one telephoto zoom. Since the E-10 had neither a truly wide-angle or a truly high-magnification telephoto, it's not entirely clear what actual range I need on either end of the scale.
On the wide end I think the decision is easier. I decided to just get the widest wide-angle zoom I could find, which is how I ended up with my 10-20mm (15-30 35mm eq) zoom. So far, that's working out pretty well for me. And now I can shoot a 180 degree panorama in two shots, which is pretty cool...
For portraits, a 50mm lens is pretty close to the 45mm lens my data says I'd want. I'd just have to step a little farther away. 50mm being the "standard" length for 35mm lenses, the basic Nikon 50mm f/1.8 lens is relatively inexpensive at $100 or so. Now, I do have that range covered with my existing zoom lens, but the fixed lens gathers way more light at f/1.8 than the zoom does at its maximum f/5.6 - doing the calculation, that's about 9 times as much light, which will make all the difference in whether I need to use a flash or if I can use available light.
On the telephoto end, I'm at a bit of a loss. I wasn't very happy with the limited telephoto on the E-10, so I'm pretty sure I'll need something considerably longer than the 17-55 lens that came with the d50, which isn't even as good as that. But how far do I need to reach? I don't think I want a lens that absolutely requires the use of a tripod for every shot, and it would be pure insanity to pay over $1,000 for an optically stabilized (VR in Nikon-ese) lens.
One interesting (but not surprising) thing is that almost all of my (semi-Macro) flower pictures are at the far end of the E-10's zoom, as well. They look pretty good at that magnification, so the equivalent focal length on the d50 (which would be about 90mm)would be a good thing to have.
I should just get the 50mm lens, I guess, and maybe get a cheap telephoto zoom and explore what range I need before plunking down the money on a "serious" telephoto lens.