Cover the Range With a Zoom Lens

Before I talk about zoom lenses, make sure you understand focal length.

Pop Quiz: What's the difference between a wide angle 28mm lens and a 600mm super-telephoto?

If you know the answer, then you're ready to tackle the information on this page.

Not 100% sure? Read more about focal length first, so that you can really understand what a variable focal length zoom lens can do for you.

Zoom Lens Defined

Simply put, you can change the focal length of a zoom lens.

Zoom lenses are common on compact digital cameras. On compact cameras, the manufacturers will say that a camera has a 3x or 10x zoom.

Not so with digital SLR lenses. The range of a zoom lens for a digital SLR is specified with focal length.

Let's use the example of a 28mm to 135mm zoom lens. The short focal length (28mm) represents the wide angle setting of the zoom, which captures all of the scenery in your photo.

The long focal length is also called the telephoto setting (135mm) and this allows you to focus in on details of the scene.

Focal Length Ranges

You can't find a zoom lens for every occasion.

In the introduction to focal length, I noted that lenses specialize in 4 different focal lengths: wide angle, standard, telephoto and super-telephoto.

Since zooms aren't limited to one focal length, they specialize in focal length ranges.

Wide Angle to Wide Angle	Range: 11mm to 28mm
Wide Angle to Telephoto	Range: 28mm to 300mm
Telephoto to Telephoto	Range: 100mm to 600mm

If you're looking at a zoom lens, it will be described like this:

[wide angle number]-[zoom number]

Examples:

A 16-35mm zoom covers the entire range from 16mm at wide angle to 35mm (also wide angle)
A 28-135mm zoom covers 28mm at wide angle to 135mm telephoto
A 100-400mm zoom covers 100mm telephoto to 400mm super-telephoto

Zoom Power

A powerful zoom has a wide range from wide angle to zoom.

Here's the easiest way to tell how powerful a zoom is: subtract the small number from the large number.

For example, the power of a 28-135mm zoom is 107. The power of a 100-400mm zoom is 300.

The 100-400mm has a more powerful zoom than the 28-135.

The advantage of a more powerful zoom is that you have flexibility to switch from a very wide angle view to telephoto. No matter what you're photographing, one lens will do the trick.

There are two disadvantages: more powerful zooms cost more (a lot more!) and they are heavier and bulkier than less powerful zooms.