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= ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
s
section, we can determine the field of view using the same 25mm eyepiece that is supplied standard with all Omni XLT
nuing
tance
apparent field of each eyepiece that Celestron manufactures is found in the Celestron Accessory
Determining the field of view is important if you want to get an idea of the angular size of the object you are observing.
calculate the actual field of view, divide the apparent field of the eyepiece (supplied by the eyepiece manufacturer) by th
magnification. In equation format, the formula looks like this:
Apparent Field of Eyepiece
True Field
Magnification
As you can see, before determining the field of view, you must calculate the magnification. Using the example in the previou
telescopes. The 25mm eyepiece has an apparent field of view of 50°. Divide the 50° by the magnification, which is 40 power.
This yields an actual field of 1.25°.
To convert degrees to feet at 1,000 yards, which is more useful for terrestrial observing, simply multiply by 52.5. Conti
with our example
, multiply the angular field of 1.25° by 52.5. This produces a linear field width of 65.6 feet at a dis
of one thousand yards. The
Catalog (# 93685).
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are a few things to remember to ensure you get the best possible image.
ary in
part of a window to the next. This inconsistency can and will affect the ability to focus your telescope.
In most cases you will not be able to achieve a truly sharp image, while in some cases, you may actually see a double image.
loo is includes asphalt parking lots on hot summer days or
Hazy skies, fog, and mist can also make it difficult to focus when viewing terrestrially. The amount of detail seen under
these conditions is greatly reduced. Also, when photographing under these conditions, the processed film may come out a
n observing with an eyepiece
attached to the telescope. When using a camera, however, you should always wear corrective lenses to ensure the sharpest
When working with any optical instrument, there
• Never look through window glass. Glass found in household windows is optically imperfect, and as a result, may v
thickness from one
• Never k across or over objects that are producing heat waves. Th
building rooftops.
•
little grainier than normal with lower contrast and underexposed.
• If you wear corrective lenses (specifically glasses), you may want to remove them whe
possible focus. If you have astigmatism, corrective lenses must be worn at all times.
22