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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:
= ⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯⎯
True Field
As you can see, before determining the field of view, you must calculate the magnification. Using the example in the previou
section, we can determine the field of view using the same 25mm eyepiece that is supplied standard with all Omni XLT
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
, multiply the angular field of 1.25
with our example
of one thousand yards. The
apparent field of each eyepiece that Celestron manufactures is found in the Celestron Accessory
Catalog (# 93685).
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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
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.
•
Never
loo
k across or over objects that are producing heat waves. Th
building rooftops.
•
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
little grainier than normal with lower contrast and underexposed.
•
If you wear corrective lenses (specifically glasses), you may want to remove them whe
attached to the telescope. When using a camera, however, you should always wear corrective lenses to ensure the sharpest
possible focus. If you have astigmatism, corrective lenses must be worn at all times.
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Apparent Field of Eyepiece
Magnification
° by 52.5. This produces
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are a few things to remember to ensure you get the best possible image.
a linear field width of 65.6
is includes asphalt parking lots on hot summer days or
n observing with an eyepiece
22
To
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nuing
feet at a dis
tance
ary in
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