Thursday, January 12, 2006

On the subject of camera lenses

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
9.0mm 1352
10.0mm 70
11.0mm 57
12.0mm 51
13.0mm 39
14.0mm 43
15.0mm 50
16.0mm 34
17.0mm 103
18.0mm 42
19.0mm 41
20.0mm 49
21.0mm 15
22.0mm 27
23.0mm 11
24.0mm 25
25.0mm 8
26.0mm 35
27.0mm 16
28.0mm 16
29.0mm 15
30.0mm 16
31.0mm 22
32.0mm 34
34.0mm 21
36.0mm 488

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.


Mat said...

I'm trying to make the same decision that you are - deciding what lens to get for a new D50. From what I can assess, the 50mm is a must have and for the price the kit (18-55mm) lens is pretty decent. There are definatley better ones out there for a couple hundred more but I guess it depends on how serious you are about photography. Don't forget about the 1.5x multiplier so 55mm might actually seem like a lot more zoom than it sounds.

Mark Bessey said...

Thanks for the comment. I suspect the "right" answer is to get something that gets me well into far telephoto range, like the 55-200 zoom, then use that and the kit lens for a while.

Then I can run the same sort of stastical analysis again, and see what focal lengths I'm actually using.

Zachery Bir said...

Keep in mind that for non-DX lenses, you're getting a multiplier of 1.5x the focal length. That 50mm lens is actually a 75mm lens for the D50 (and the D70, and my D200).

Mark Bessey said...

Zachery, You're right, though the multiplier is the same whether the lenses are DX or non-DX.

The usual range of portrait focal lengths for the 35mm format is from about 55mm to 135mm, depending on the situation.

That translates to roughly 39-90mm on the Dx-format digitals. Some experimentation with my 105mm macro lens shows that it's pretty good for portraits, though you do need to back way up.

I still ahven't gotten that 50mm f/1.8 yet, though...