Read this tip to make your life smarter, better, faster and wiser. LifeTips is the place to go when you need to know about Digital Photograhy Basics and other Digital Photography topics.
Some digital cameras have lenses with a fixed maximum aperture. For example, f-2.8 or f-4.0. Other cameras have variable maximum apertures. This is usually marked on the camera or lens as f-3.5 - 5.6, or something similar. So what's going on here?
It's simply the need for affordable zoom lenses.
You see, the f-number is actually a ratio. It essentially compares how wide the lens opens to the focal length of the lens. For most people, that's a little confusing, so let's look at my favorite metaphor:
Let's say you're inside a huge cardboard box. You're sitting in a chair eight feet from the box's far wall and you want to read a book.
Now let's say I cut a 4" hole in that far wall. It isn't going to let a lot of light into an eight-foot box, is it? You probably wouldn't be able to read your book. But a three-foot hole in the side of the box would let in a lot more light. And then maybe you could read.
But let's say the box is only three feet long. In a box that short, you just may be able to read your book by the light from a 4" hole.
It's very much the same with lenses. The longer the lens, the wider it has to be able to open to admit a useful amount of light. And that can mean a lot of expensive glass. How expensive? Well, a Nikon 80 - 200 mm f-2.8 zoom lens will run you about $1,000 or more.
Imagine tacking a few hundred dollars onto the cost of a digital point-and-shoot camera. It would be an affordable option for a lot less people. And that's why digital camera manufacturers use variable maximum apertures: less glass and less cost.
So, when you see a camera with an f-3.5 - 5.6 (for example) lens, you know the zoom will be a lot faster at the wide-angle end than at the telephoto end. That's a good point to keep in mind when you're choosing your new digital camera.
|Jennifer Mathes, Ph.D.|