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:
Apparent Field of Eyepiece
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 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
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
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
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.
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