7.5 LONG LENSES

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A lens zoomed in on a subject acts somewhat like a telescope: 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. Zooming in like this is ideal for wildlife, portrait, and candid photography, whenever getting close to a subject might disturb it.

When you zoom in on a subject, depth of field gets shallower so you must focus carefully. Also, zooming in visually compresses space, making objects in the scene appear closer together than they actually are.

The primary drawback of zooming in is that it gives you a smaller maximum aperture. This smaller maximum aperture may require a longer shutter speed and since a long lens magnifies movement, just as it magnifies the subject, you may have to use a tripod instead of hand-holding the camera.

Zooming in 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.

For a telephoto view, you can zoom the lens all the way in. For even more magnification, some cameras have optional lens converters that give you even longer focal lengths.

When the lineup of cement trucks (bottom) is shot head-on with a long lens (top) 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 lenses come in two varieties; optical and digital zooms. An optical zoom lens 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 lens 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.