Celestron CPC Deluxe 800 HD Computerized Telescope CPC Deluxe HD Manual - Page 21

>> 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. Mirror Clutch Knobs FIGURE 5-4 >> 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: Magnification - Focal Length of Telescope (mm) Focal Length of Eyepiece (mm) 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. >> 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: 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 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). >> 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. >> www.celestron.com 19