User manual CELESTRON NEXSTAR 5I Instruction Manual

[. . . ] However, there are a few things to consider before using your telescope that will ensure your safety and protect your equipment. Warning Y Y Y Y Never look directly at the sun with the naked eye or with a telescope (unless you have the proper solar filter). Never use your telescope to project an image of the sun onto any surface. Internal heat build-up can damage the telescope and any accessories attached to it. Internal heat build-up inside the telescope can cause these devices to crack or break, allowing unfiltered sunlight to pass through to the eye. [. . . ] In equation format, the formula looks like this: Focal Length of Telescope (mm) Magnification = Focal Length of Eyepiece (mm) Let's say, for example, you are using the 25mm Plossl eyepiece. To determine the magnification you simply divide the focal length of your telescope (the NexStar 8i has a focal length of about 2000mm) by the focal length of the eyepiece, 25mm. 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. 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 NexStar 8 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 25mm eyepiece. This yields an actual field of . 63°, or a little more than a half of a 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 . 63° by 52. 5. This produces a linear field width of 33 feet at a 34 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. 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. 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. [. . . ] As a condition to the obligation of Celestron to repair or replace such product, the product must be returned to Celestron together with proof-of-purchase satisfactory to Celestron. The Proper Return Authorization Number must be obtained from Celestron in advance of return. Call Celestron at (310) 328-9560 to receive the number to be displayed on the outside of your shipping container. All returns must be accompanied by a written statement setting forth the name, address, and daytime telephone number of the owner, together with a brief description of any claimed defects. [. . . ]