Choice of a Lens

Digital camera lenses are described in two ways: focal length, given in mm, and optical magnification, given as 3x, 12x, or the like. The second form of description can be misleading: a 3x lens won't necessarily enlarge a scene by a factor of three. To help you understand differences between lenses, we've taken a series of pictures of a member of the group, Jason Schieck, standing in front of the new Austin City Hall. Everything remained the same in the pictures except the focal length of the lens. Simply put, the larger the focal length, the greater the magnification. Similarly, the smaller the focal length, the greater the angle taken in by the camera.

Small Camera

A typical small digital camera will have a focal length ranging from roughly 38 mm to 114 mm, and will be listed as a 3x zoom: it is a 3x optical zoom because 114/38 = 3. The 35 mm picture (below) represents the widest angle available to take panoramic or large-group pictures; the 100 mm picture (below) represents almost as much magnification as a small digital camera can produce.

Wide Angle

Suppose it's important to take a picture of a large group or of a broad landscape. You will need a small minimum focal length (the first number in the range), perhaps as low as 28 mm or 24 mm (see below for examples). There are a few small cameras with a 28 mm focal length, and only large cameras have the option of still smaller focal lengths.

Telephoto Lens

Taking close up pictures (of nature, sports, or whatever) often requires cameras with a large maximum focal length. 200–300 mm lenses can noticeably enlarge a scene: the pictures below were taken from the same distance as were the pictures above. Situations requiring a great deal of magnification require large cameras; telephoto cameras with fixed lenses can have maximum focal lengths exceeding 400 mm, but small cameras never do even with an add on lens that will increase the focal length at the expense of less picture quality.

The focal length on a telephoto camera with a fixed lens can exceed 400mm so you will have to judge how large Jason's nose would be in such a picture.

Choice Criteria

You need a large camera when:

1. You want to take pictures with a focal length of 200 mm or greater (i.e., greater than five times the standard magnification of a small camera). (Note that some small Canon and Sony cameras have add-on lenses that can increase the effective focal length at the cost of picture quality. This may be a worthwhile compromise if having a small camera is very important to you.)

2. You want to take wide-angle pictures with a focal length of less than 28 mm. (Again, there are add-on lenses for some small cameras that will allow for wider-angle shots at the expense of picture quality.

Your choices among large cameras are:

• dSLRs, for which you purchase interchangeable lenses that include your desired focal length (for example, you may purchase a 24-85 mm lens for wide-angle work and a 70-300 mm lens for zoom work)
• Telephotos, which have great magnification but poor wide-angle capacity (you can expect a focal length from roughly 35 mm to 430 mm).
• Prosumers, which have considerable variation in the lenses (some have 24-85 mm, others have 28-200 mm, and so on). Prosumer cameras are a better choice than telephoto cameras if you are willing to give up magnifying capacity to get better wide-angle capacity.