Absolute Beginner's Guide to Digital Photography

CHAPTER 4 THE IMPORTANCE OF LENSES 61

lens focal length

aperture diameter

f-stop =

If the focal length of the lens is 50mm, you need a lens opening of 12.5mm to pro-

duce an f/4 aperture.

If the focal length of the lens is 300mm, you need a lens opening of 75mm to pro-

duce an f/4 aperture.

50mm lens

12.5mm lens opening

50

12.5

= = f/4

300mm lens

75mm lens opening

300

75

= = f/4

The Absolute Minimum

Lenses are the most important part of a camera system. The quality of your images

depends entirely on the glass between the subject and the film or CCD. If you own a

non-SLR digital or film camera, you’re stuck with a specific lens. If you own an SLR,

however, your choices are much greater. Keep these tips in mind when considering

the cost or purpose of a lens:

■ Buy the best lens or lenses you can afford. For SLR owners, used lenses are

fine as long as they are high quality.

■ A “normal” focal length lens, in the 35–85mm range, is by far the most valu-

able lens you can own.

■ Digital camera sensors are physically smaller than a 35mm film frame. This

causes regular lenses to have a longer focal length. A 35mm lens for example

might actually be 50mm on a digital camera SLR.

■ Fixed-focal length lenses on consumer-level digital cameras are often not that

large. This results in slower shutter speeds or more noise in low-light situa-

tions.

■ Telephoto lenses require you use a monopod or tripod. Invest in one and use

it whenever you take pictures with a telephoto.

■ Fisheye lenses are fun, but full-frame fisheye lenses are much more useful.