Datasheet

■ BRIDGING THE FILM/DIGITAL GAP

Note: Because digital camera manufacturers calculate 35mm equivalents using different

criteria, allow for up to a 15 percent variation when comparing one digital camera’s equivalent

focal length with another’s.

If all else fails, there is a relatively straightforward relationship between the diag-

onal dimension of a sensor (or film) and what is considered a normal focal length. If,

for example, the diagonal measurement of a sensor is 12mm (as it is for the sensor used

in the Nikon Coolpix 990), then the normal focal length is 12mm. (The Nikon actually

comes with an 8mm–24mm zoom lens, which translates to 38mm–115mm in 35mm

film equivalence.) The diagonal measurement for the sensor in the Canon EOS-5D is

the same as 35mm film—about 43mm—which explains why a 50mm “normal” lens on

a Canon camera will provide the same field of view on a 35mm film camera. (Many

people have been taught that a 50mm lens is a normal lens for a 35mm camera, but as

you can see by the math, 50mm doesn’t fully represent the normal human field of view.

Many pros consider a 35mm lens “normal” for a 35mm film camera.) Some manufac-

turers list the diagonal measure of a sensor with the camera’s specifications.

Note: Lens zoom capabilities are sometimes expressed in multiplication style, such as 3x

or 6x. This refers to zoom range, starting at the widest angle. A 40mm, 4x lens, therefore, has

a range of 40mm–160mm. A 35mm, 10x lens has a very large range, from 35mm to 350mm.

Digital zoom is something altogether different. It has nothing to do with the lens itself, but

refers to software interpolation that occurs after an image has been captured.

Knowing what you do now, you’ll better understand why it’s more difficult to

find a digital camera equipped with a lens that has less than a 30mm focal-length equiv-

alent. Until recently, it was only the more expensive digital cameras with larger sensors

that gave you the option of wider lenses. Even then, if you place a 12mm fisheye lens

on, say, a Nikon D 200, it will still be equivalent to only about 20mm on a 35mm cam-

era—which is wide, but not super wide. (Accessory, add-on lenses can extend the wide-

angle capabilities of many digital cameras to a degree; however, there is some trade-off

in quality.) Camera manufacturers are getting around this limitation by designing lenses

specifically for smaller sensors. The Nikon DX lens series, for example, includes a rela-

tively affordable 10.5mm F2.8 fisheye, with an equivalent field of view of 15.75mm.

Kodak also offers a clever solution to the wide-angle conundrum: a digital camera with

two lenses and two sensors. The Kodak EasyShare V570 boasts a 23mm equivalent lens

and a 37mm–117mm equivalent zoom lens built into one body.

Bottom line: Focal-length equivalents will vary between different digital cameras with differ-

ently sized sensors. Don’t expect a 1:1 relationship between the angle of view of a lens used on a digi-

tal camera and the lens used on a 35mm film camera. Finally, the smaller the sensor, the less chance

your camera will provide an effective wide-angle view.

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