A Short Course Book
Using Your Digital Camera
A Guide To Great Photographs

Long Focal Lengths

 
 
A long lens doesn't compress space (bottom), it just captures the compression that's already in the distant part of a scene (top).
 
 
A long lens is essential for much nature photography.
 
 
Click to explore optical and digital zoom.
 
 
These two photos were taken with the same camera. One was taken using optical zoom (top) and the other with digital zoom from farther away (bottom). The one taken with optical zoom is much sharper.
A long focal length lens acts somewhat like a telescope in that it magnifies the image of your subject. This is especially useful when you can't get close to your subject—or don't want to. Long lenses are ideal for wildlife, portrait, and candid photography, whenever getting close to a subject might disturb it.

As the focal length of a lens increases, the depth of field gets shallower so you must focus more carefully. Also, a long lens visually compresses space, making objects in the scene appear closer together than they actually are. The primary drawback of a long lens is that most (but not all) such lenses have a smaller maximum aperture. This may force you to use a slower shutter speed. Since a long lens magnifies movement, just as it magnifies the subject, you may also have to use a tripod instead of hand-holding the camera. If your camera has a fixed lens, you may be able to use a tele lens converter to give it an even longer focal length.

A long lens makes distant objects appear compressed. Here a long lens has been used to "compress" a street scene at the foot of the Rocky Mountains in Colorado.

When the lineup of cement trucks (bottom right) is shot head-on with a long lens (above left) they appear much closer together then they really are. This is actually due to the distance from the subject, not the focal length of the lens, but the effect is easy to get with a long lens.

A long lens makes the sun look larger in relation to foreground objects.

Digital Zoom

Zoom comes in two varieties; optical and digital. An optical zoom actually changes the amount of the scene falling on the image sensor. Every pixel in the image contains unique data so the final photo is sharp and clear. A digital zoom, found on many fixed lens cameras, uses sleight of hand by taking a part of the normal image falling on the sensor and then enlarging it to fill the sensor. It does this by adding new pixels to the image using interpolation. The interpolated image doesn't have as many unique pixels as one taken with an optical zoom so is inferior. In fact, you don't even need this zoom feature because you can get exactly the same effect just by cropping a normal image in a photo-editing program and then enlarging it.


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