Celestron 102mm Buku Petunjuk - Halaman 10

Jelajahi secara online atau unduh pdf Buku Petunjuk untuk Teleskop Celestron 102mm. Celestron 102mm 17 halaman. 80mm/102mm wide view spotting scope

Field of View

Determining the field of view is important if you want to get an idea of the size of the object you

are observing. To calculate the actual field of view, divide the apparent field of the eyepiece

(supplied by the eyepiece manufacturer) by the magnification. In equation format, the formula

looks like this:

True Field (in degrees) =

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

using the same 25mm eyepiece. The 25mm eyepiece has an apparent field of view of 50°. Divide

the 50° by the magnification, which is 20 power. This yields an actual field of 2.5°, or two and a

half degrees. To convert this to feet at one thousand yards, multiply the actual field of 2.5° by

52.5. This gives us a field width of 131 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.

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.

Apparent Field of Eyepiece

Magnification

Releasing

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

the

shutter

manually

can

cause