Instruction manual

when digital zoom is necessary to get a photo of a distant object, the truth

is that it does not create as good an image as can be recorded optically.

Don’t use digital zoom! Turn if off (if your camera has a setting for this),

or be careful not to activate it when you zoom.

Focal Length

Focal length is a measurement of the magnifying power of a lens, or the

distance (in ‘mm’) between the lens and the focal plane (the area upon which the

lens is focusing). The longer the focal length, the more magnification a lens will

provide. However, as magnification increase the field of view decreases.

The human eye has a field of view of 50°-55°; so a 55mm lens is considered

“normal.” When you “zoom in” on a subject you are increasing the focal length of

the lens. This produces more magnification and a narrower field of view. Zoom

lenses offer great flexibility in terms of framing and camera position.

All lenses project a circular image onto the focal plane. The image sensor

(sitting on the focal plane) records a rectangular crop from the middle of that

circle. Thus a larger image sensor will provide a larger crop. Because of this, the

same lens placed on a camera with a different sized sensor will yield a different

field of view.

The 35mm frame size has been the standard for so long that most think in

terms of 35mm when they consider a particular focal length. So, a 50 mm lens is

considered “normal,’ while a 28mm lens is considered wide-angle and a 200mm is

considered telephoto.

Since all point-and-shoot cameras and most SLR cameras have sensors that

are smaller than a 35mm frame, when you place the same lens on a camera with

this smaller sensor they will have the narrower field of view of a more telephoto

lens. To learn what the equivalent focal length is in terms of a 35mm camera, you

must multiply the actual focal length by a multiplication factor to determine the

35mm focal length equivalency. Most Nikon SLRs have a focal length multiplier of

1.5 (Canon EOS cameras are usually 1.6), so a 50mm lens placed on a Nikon

SLR will have the same crop as a 75mm lens on a full-frame camera (1.5 x 50mm

= 75mm).

NOTE: This cropping factor can be very handy when using telephoto lenses.

For example, if you place a full-frame 200mm lens on a Nikon SLR you get the

same crop as a 300mm lens (1.5 x 200mm = 300mm). [Conversely, when you fit

a 28mm wide-angle lens onto this camera it will have a full-frame equivalent crop

of 42mm, which is not very wide.]

Many camera vendors now make lenses specifically engineered for their

cameras that have smaller sensors. Nikon denotes these lenses with the “DX”

label (Canon uses “EF-S”).

Anything shorter than about a 24mm lens on a digital SLR will include the

plane's wing struts or landing gear in the photo. Medium lenses (most likely to

come with your camera) are useful for overall views, and those with a 3x optical

zoom work fine for CAP purposes. Long lenses work very well, and an 80-200

mm f/2.8 zoom is ideal. Lenses longer than 200 mm are tough to use since their

slower speeds tend to require longer shutter speeds, and the longer focal length

dictates even shorter shutter speeds.