Celestron CPC Deluxe 1100 HD Computerized Telescope - Manual (Page 21)

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>> Mirror Support Clutches
The EdgeHD Optical tube is equipped with mirror tension clutches to
help support and minimize lateral movement of the primary mirror
during astrophotography .
To use the mirror clutches:
1. Use the focus knob to adjust the primary mirror to the desired focus.
2. Once in focus, turn the two mirror lock knobs clockwise until both are
very tight and can be turned no further .
Warning! Once the mirror is locked down, do not turn the focuser
knob without loosening the mirror locks first. Although turning
the focus knob should not damage the telescope, undue stress can
be placed on the focus mechanisms causing excessive image shift
while focusing.
>> Calculating Magnification
You can change the power of your telescope just by changing the
eyepiece (ocular). To determine the magnification of your telescope,
simply divide the focal length of the telescope by the focal length of the
eyepiece used. In equation format, the formula looks like this:
Let’s say, for example, you are using the 40 mm Plössl eyepiece . To
determine the magnification you simply divide the focal length of your
telescope (the CPC 800, for example, has a focal length of 2032 mm) by
the focal length of the eyepiece, 40 mm . Dividing 2032 by 40 yields a
magnification of 51 power.
Although the power is variable, each instrument under average skies
has a limit to the highest useful magnification. The general rule is that
60 power can be used for every inch of aperture. For example, the
CPC 800 is 8 inches in diameter. Multiplying 8 by 60 gives a maximum
useful magnification of 480 power. Although this is the maximum useful
magnification, most observing is done in the range of 20 to 35 power for
every inch of aperture which is 160 to 280 times for the CPC 800 telescope.
Magnification –
Focal Length of Telescope (mm)
Focal Length of Eyepiece (mm)
>> Determining Field of View
Determining the field of view is important if you want to get an idea of
the angular 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:
As you can see, before determining the field of view, you must calculate
the magnification. Using the example in the previous section, we can
determine the field of view using the same 40 mm eyepiece. The 40 mm
Plössl eyepiece has an apparent field of view of 46°. Divide the 46° by
the magnification, which is 51 power. This yields an actual field of .9°, or
almost a full degree .
To convert degrees to feet at 1,000 yards, which is more useful for
terrestrial observing, simply multiply by 52 .5 . Continuing with our
example, multiply the angular field .9° by 52.5. This produces a linear
field width of 47 feet at a distance of one thousand yards. The apparent
field of each eyepiece that Celestron manufactures is found in the
Celestron Accessory Catalog (#93685).
True Field –
Apparent Field of Eyepiece
Magnification
>> General Observing Hints
When working with any optical instrument, there are a few things to
remember to ensure you get the best possible image .
• Never look through window glass. Glass found in household windows
is optically imperfect, and as a result, may vary in 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 look across or over objects that are producing heat waves. This
includes asphalt parking lots on hot summer days or 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 when observing with an eyepiece attached to the
telescope . When using a camera, however, you should always wear
corrective lenses to ensure the sharpest possible focus. If you have a
stigmatism, corrective lenses must be worn at all times .
FIGURE 5-4
Mirror
Clutch
Knobs