This level of magnification assumes you have ideal conditions for viewing, however. The clearest, sharpest views will always be achieved at lower powers.
Keep in mind that as you increase magnification, the bright- ness of the object viewed will decrease; this is an inherent principle of the laws of physics and cannot be avoided. If mag- nification is doubled, an image appears four times dimmer. If magnification is tripled, image brightness is reduced by a fac- tor of nine!
The
Determining the 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:
You can use a commercially made lens cleaner or mix your own. A good cleaning solution is isopropyl alcohol mixed with distilled water. The solution should be 60% isopropyl alcohol and 40% distilled water. Or, liquid dish soap diluted with water (a couple of drops per one quart of water) can be used.
Occasionally, you may experience dew
If moisture condenses on the inside of the corrector, remove the accessories from the rear cell of the telescope. Place the telescope in a
To minimize the need to clean your telescope, replace all lens covers once you have finished using it. Since the rear cell is NOT sealed, the cover should be placed over the opening when not in use. This will prevent contaminants from entering the optical tube.
Internal adjustments and cleaning should be done only by an authorized repair department. If your telescope is in need of internal cleaning, please call Orion for a return authorization number and price quote.
Apparent Field of Eyepiece
Magnification
= True Field
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 26mm eyepiece. A 26mm Plössl eyepiece has an apparent field of view of 52°. Divide 52 by the magnification, which is 78. This yields an actual field of 1.5°.
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 1.5° by 52.5. This produces a linear field width of 78.8 feet at a distance of 1,000 yards.
Care and Cleaning of the Optics
Occasionally, dust and/or moisture may build up on the correc- tor plate of your telescope. Special care should be taken when cleaning any instrument so as not to damage the optics.
If dust has built up on the corrector plate, remove it with a brush (made of camel’s hair) or a blower bulb. Then, use an optical cleaning solution and white tissue paper to remove any remaining debris. Apply the solution to the tissue (not to the glass) and then apply the tissue paper to the lens.
Collimation screws
Collimation | Figure 6. The three collimation |
screws are located on the front of | |
The optical performance | the secondary mirror housing. |
|
of your telescope is directly related to its collimation, that is the alignment of its optical system. Your telescope was collimated at the factory after it was completely assembled. However, if the telescope is dropped or jarred severely during transport, it may have to be
To check the collimation of your telescope you will need a light source. A bright star near the zenith is ideal since there is a minimal amount of atmospheric distortion. Make sure that tracking is on so that you won’t have to manually track the star.
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