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Using the example in the previous section, we can determine the field of view using the same 25mm eyepiece. 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 view of 1.25°. 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 1.4° by 52.5. This produces a linear field width of 66 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). G GGe een nne eer rra aal ll O OOb bbs sse eer rrv vvi iin nng gg H HHi iin nnt tts ss 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 astigmatism, corrective lenses must be worn at all times. 27 With your telescope set up, you are ready to use it for observing. This section covers visual observing hints for both solar system and deep sky objects as well as general observing conditions which will affect your ability to observe. O OOb bbs sse eer rrv vvi iin nng gg t tth hhe ee M MMo ooo oon nn Often, it is tempting to look at the Moon when it is full. At this time, the face we see is fully illuminated and its light can be overpowering. In addition, little or no contrast can be seen during this phase. One of the best times to observe the Moon is during its partial phases (around the time of first or third quarter). Long shadows reveal a great amount of detail on the lunar surface. At low power you will be able to see most of the lunar disk at one time. Change to higher power (magnification) to focus in on a smaller area. Choose the lunar tracking rate from the NexStar's MENU tracking rate options to keep the moon centered in the eyepiece even at high magnifications. L LLu uun nna aar rr O OOb bbs sse eer rrv vvi iin nng gg H HHi iin nnt tts ss • To increase contrast and bring out detail on the lunar surface, use eyepiece filters. A yellow filter works well at improving contrast while a neutral density or polarizing filter will reduce overall surface brightness and glare. O OOb bbs sse eer rrv vvi iin nng gg t tth hhe ee P PPl lla aan nne eet tts ss Other fascinating targets include the five naked eye planets. You can see Venus go through its lunar-like phases. Mars can reveal a host of surface detail and one, if not both, of its polar caps. You will be able to see the cloud belts of Jupiter and the great Red Spot (if it is visible at the time you are observing). In addition, you will also be able to see the moons of Jupiter as they orbit the giant planet. Saturn, with its beautiful rings, is easily visible at moderate power. P PPl lla aan nne eet tta aar rry yy O OOb bbs sse eer rrv vvi iin nng gg H HHi iin nnt tts ss • Remember that atmospheric conditions are usually the limiting factor on how much planetary detail will be visible. So, avoid observing the planets when they are low on the horizon or when they are directly over a source of radiating heat, such as a rooftop or chimney. See the "Seeing Conditions" section later in this section. • To increase contrast and bring out detail on the planetary surface, try using Celestron eyepiece filters. O OOb bbs sse eer rrv vvi iin nng gg t tth hhe ee S SSu uun nn Although overlooked by many amateur astronomers, solar observation is both rewarding and fun. However, because the Sun is so bright, special precautions must be taken when observing our star so as not to damage your eyes or your telescope. Never project an image of the Sun through the telescope. Tremendous heat build-up may result inside the optical tube. This can damage the telescope and/or any accessories attached to the telescope. 28 For safe solar viewing, use a Celestron solar filter (see Optional Accessories section of...

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