Celestron Omni CG-4 Telescope Mount Telescope Basics - Page 4

can greatly enlarge the image, but remember that the contrast and brightness will be low due to the high magnification. High powers can be used occasionally when conditions allow - you will achieve the power but the image will be dark with low contrast because you have magnified the object to considerably. For the brightest images with the highest contrast levels, use lower powers. 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 fmiealdgnoifficthaetioenyM.eIapngieencqifeiuca(asttuiioopnnplf=ioerdmFFboaoyctc,aattlhlhLeLeeemnfnogagrtnmthhuuofoalfafcTtEleuoylroeeeksprs)cieoblicpkyeeeth(t(mmheimsm:)) True (Actual) Field of View = Apparent Field of Eyepiece Magnification As you can see, before determining the field of view, you must calculate the magnification. Using the example above, we can determine the field of view using the same 25 mm eyepiece. The 25 mm 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 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 of 1.25° by 52.5 and this produces a linear field width of 65.6 feet at a distance of one thousand yards. The apparent field of each eyepiece that Celestron supplies with its telescopes can be found under specifications for the particular telescope model on Celestron's website. General Observing Hints When using 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. • 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. ©2011 Celestron • All rights reserved. 4