Orion 80-A Terrestrial Viewing, Calculating Magnification Power, Care & Maintenance

is important that you find an observing site well away from light pollution. Take plenty of time to let your eyes adjust to the darkness. Don’t expect these objects to appear like the photographs you see in books and magazines; most will look like dim gray “ghosts.” (Our eyes are not sensitive enough to see color in deep-sky objects except in few of the brightest ones.) But as you become more experienced and your observing skills improve, you will be able to coax out more and more intricate details.

Terrestrial Viewing

Many people enjoy using their telescope to view objects such as boats, birds and wildlife. The ShortTube 80-A is an excellent instrument for observing during the daylight hours.

For terrestrial applications, we recommend mounting the ShortTube 80-A on an altazimuth-style telescope mount or camera tripod, which allow simple vertical (altitude) and horizontal (azimuth) motions. We also recommend using a 45° correct-image prism diagonal instead of the supplied star diagonal. A correct-image prism diagonal is designed for daytime use and yields a properly oriented view (same as the naked eye).

Calculating Magnification

(Power)

It is desirable to have a range of eyepieces of different focal lengths, to allow viewing over a range of magnifications. To calculate the magnification, or power, of a telescope, simply divide the focal length of the telescope by the focal length of the eyepiece:

Telescope F.L. ÷ Eyepiece F.L.=Magnification

For example, the ShortTube 80-A, which has a focal length of 400mm, used in combination with the supplied 20mm eyepiece, yields a magnification of

400 ÷ 20 = 20x.

Every telescope has a useful limit of magnification of about 45x-60x per inch of aperture, which is 140x-180x for the ShortTube 80-A. Claims of higher power by some telescope manufacturers are a misleading advertising gimmick and should be dismissed. Keep in mind that at higher powers, an image will always be dimmer and less sharp (this is a fundamental law of optics). The steadiness of the air (the “seeing”) can also limit how much magnification an image can tolerate.

Always start viewing with your lowest-power (longest focal length) eyepiece in the telescope. After you have located and looked at the object with it, you can try switching to a higher-power eyepiece, like the supplied 9mm Expanse eye- piece, to ferret out more detail. If the image you see is not crisp and steady, reduce the magnification by switching to a longer-focal-length eyepiece. As a general rule, a small but

well-resolved image will show more detail and provide a more enjoyable view than a dim and fuzzy, overmagnified image.

Photography with the ShortTube 80-A

With an optional camera adapter, the ShortTube 80-A becomes a 400mm f/5 telephoto lens for a single-lens reflex camera. For long-distance terrestrial or astronomical pho- tography, you need only a T-ring for your particular camera model. The T-ring attaches to your particular camera model and threads onto the ShortTube’s focuser drawtube, cou- pling the camera body to the telescope (Figure 3).

Figure 3. The ShortTube 80-A with 35mm SLR camera

attached.

For closer-range (less than 1/4-mile) terrestrial photography, you need both a T-ring for your camera and a T-adapter (#5264), which provides the extra focus travel needed. Remove the nosepiece from the camera adapter; the body of the adapter will not be needed here. Connect the T-ring to your camera body (remove any camera lenses first), and connect the nosepiece of the camera adapter to the T-ring. Now, insert the entire assembly into the focuser’s drawtube (remove the eyepiece and diagonal), and secure with the thumbscrew on the drawtube. Be sure to tighten the thumb- screw, or your camera could fall to the ground!

Use the camera’s viewfinder to frame the picture. Use the telescope’s focuser to focus the image. Tighten the focus lock thumbscrew on the telescope’s focuser to make sure the camera does not slip out of focus.

You may want to consider using a remote shutter release instead of the shutter release on the camera. Touching the camera can vibrate the system and blur the resulting photo- graphic image. Also, be sure to use a solid tripod.

Care & Maintenance

Give your telescope reasonable care and it will last a life- time. Store it indoors or in a dry garage. Do not leave the telescope outside except when using it. The optical tube is aluminum and has a smooth painted surface that should resist scratches and smudges. If a scratch does appear on the tube, it will not harm the telescope. If you wish, you can apply some white auto touch-up paint to the scratch. Smudges on the tube can be wiped off with standard house- hold cleaning fluid.

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