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Apparent Field of Eyepiece

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True Field (in degrees) =

Magnification

Using the example we started with in the previous section, we can determine the field of view using the

same 30mm eyepiece. The 30mm eyepiece has an apparent field of view of 50°. Divide the 50° by the

magnification, which is 33 power. This yields an actual field of 1.5°, or a degree and a half. To convert this

to feet at one thousand yards, multiply the actual field of 1.5° by 52.5. This gives us a field width of 78.8

feet at one thousand yards.

PHOTOGRAPHY HINTS

Metering

Celestron spotting scopes have fixed apertures and, as a result, fixed f/ratios. To properly expose your

subjects photographically, you need to set your shutter speed accordingly. Most 35mm SLR cameras offer

through-the-lens metering which lets you know if your picture is under or overexposed. Adjustments for

proper exposures are made by changing the shutter speed. Consult your camera manual for specific

information on metering and changing shutter speeds.

Reducing Vibration

Releasing the shutter manually can cause vibrations, producing blurred photos. To reduce vibration when

tripping the shutter, use a cable release. A cable release keeps your hands clear of the camera and lens, thus

eliminating the possibility of introducing vibration. Mechanical shutter releases can be used, though air-

type releases are best.

Blurry pictures can also result from shutter speeds that are too slow. To prevent this, use films that produce

shutter speeds greater than 1/250 of a second when hand-holding the lens. If the lens is mounted on a

tripod, the exposure length is virtually unlimited.

Another way to reduce vibration is with the Vibration Suppression Pads (#93503). These pads

rest between the ground and tripod feet. They reduce the vibration amplitude and vibration time.