Monday, September 04, 2006

Basic Lens Types

Photographs are, as the Latin name implies, pictures created by light. And the first part of your camera that the light meets is the lens, making lenses a very important accessory for users of SLR cameras. "Normal" lenses are those with a focal length around 50mm. Anything much shorter than that, for example, a 28mm lens, is called a wide angle lens. Anything much longer than that, for example, an 80mm lens, is called a telephoto lens. But most lenses that people use will have a variable focal length, such as 28mm-80mm, or 80mm-210mm, and these lenses are called zoom lenses. When a zoom lens is set at a particular focal length, it will have the properties of a lens with that fixed focal length, so all this knowledge will apply to zoom lenses as well.

This article discusses the three basic lens types, normal, wide angle, and telephoto, and concludes with a short discussion of lens speed to help you avoid camera shake and to buy the best lens.

"Normal" Lenses (about 50mm)

Normal lenses will give you normal results. They are the most similar to using the human eye, and for that reason are often the lens that comes with a camera. Everyone will have a lens that is capable of being set at a normal focal length. These are perhaps the most useful of the fixed focal length lenses.

Wide Angle Lenses (35mm or less)

Wide angle lenses, or those with a short focal length, will allow you to get more into the picture. Say for example that two shooters are standing in the same spot in a subway tunnel. One shooter, who has a 50mm lens, will get a nice picture of the tracks and the tunnel ahead. The shooter with the 28mm lens, however, will not only get the tracks and tunnel, but also the pipes and wires on either side of the tunnel.

The catch is that wide angle lenses will cause distortion of the image. Things at the edge of the frame will curve. This can be used to artistic effect, but most of the time it’s a price you have to pay for using a wide angle lens. This makes them poor candidates for portrait photography, because no one wants their face distorted, their nose enlarged, and their ears shrunk.

On the positive side, wide angle lenses will cause your pictures to appear to have more depth. This creates pictures that will be much more interesting, as a rule.

Additionally, for good or ill, wide angle lenses give your pictures greater depth of field. This means that you can have a fencepost in the foreground, a field in the middleground, and a mountain in the background, and all of them will be in focus. This makes wide angle lenses ideal for most landscape photography. But it is another feature that makes them poor portraiture lenses, because you usually will want only the person in focus.

Telephoto Lenses (70mm or more)

Let’s take the example of our two shooters in the subway tunnel, and let’s add a third shooter. This one has a very nice (and expensive) 400mm telephoto lens. Instead of getting the tracks or the tunnel, this shooter is able to get a picture of the next train coming down the tunnel, even though it’s still a long way down the track.

Telephoto lenses, unlike wide angle lenses, will cause very little distortion of the image. Straight lines will appear straight, as they should, if you shoot them with a telephoto lens. This makes them ideal for portraiture, because your subject will appear as he or she appears in person.

Longer lenses also have a shallower depth of field. This is another plus for portrait photography, because you can isolate your subject very well. And of course, nobody wants you in their face while you’re taking their picture. This would make them uncomfortable.

The downside (or is it a plus?) of telephoto lenses is that they will make your pictures appear flat, as opposed to the great depth given by wide angle lenses.

Finally, telephoto lenses are a must-have for anyone serious about wildlife photography. Most animals won’t let you get in close enough to take their picture without a very long lens.

Lens Speed

One thing to keep in mind when using a longer lens is that you will more often have a problem with camera shake. Recall that a good rule of thumb is that you can shoot at a speed at least the inverse of your focal length: if you use a 200mm lens, you can handhold the camera at 1/200 second or faster, but if you are using a 28mm lens you can handhold it at 1/28 second. This means that telephoto lenses will more often require you to use a tripod.

But that is not what experts mean when they talk about lens speed. All lenses will have a maximum aperture. My wide angle lens for my Yashica FX-7 Super, for example, has a maximum aperture of f2.8. This will be designated as 1:2.8. What does it mean? Remember that wider apertures allow more light into the camera, allowing you to use faster shutter speeds. So my 28mm lens is faster than a lens designated as 1:3.5, but slower than a lens designated as 1:1.4.

Zoom lenses have another issue with maximum aperture. They have a maximum aperture at the shortest focal length, but they usually have a smaller maximum aperture at the longest focal length, meaning that the more you zoom in, the smaller your maximum aperture. The lens that I first got with my SLR, for example, is designated as 42-75mm 1:3.5-4.5. This means that it’s a zoom lens, with 42mm as the shortest focal length and 75mm as the longest focal length. It’s also a very slow (and cheap) lens, with a maximum aperture of f3.5 when zoomed all the way out, and a maximum aperture of 4.5 when zoomed all the way in.

Lenses with a larger maximum aperture are more expensive, but they are also faster and therefore more desirable.


At 9/06/2006 3:44 AM, Blogger Khorbin said...

Hey, Kelly! I just finished taking a few photos for Assignment 1, and thought I'd drop by and say hello!

Just out of curiosity, How do you get close-up shots to focus? It seems that every time I get within half a foot or so of my target, it won't focus, or at least not well. Is there a reason for this, or do I just have shaky hands?

Maybe I'll post some of my pictures on my blog tonight or tomorrow to see what you think. See you around!

At 9/06/2006 10:31 AM, Blogger Kelly said...

All lenses have some kind of limitation on how close they can focus. Your digital camera probably has a "macro" mode that will allow it to focus closer than otherwise possible, and it's often indicated by a flower-looking icon. It may also have a manual focus mode, indicated on my camera by the letters MF. This is a little more difficult to use though, because of the limited resolution of the LCD screen.


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