Orion 80-T instruction manual Terrestrial Viewing, Astronomical Viewing, Do You Wear Eyeglasses?

Do You Wear Eyeglasses?

If you wear eyeglasses, you may be able to keep them on while you observe, if your eyepieces have enough “eye relief” to allow you to see the whole field of view. You can find out by looking through the eyepiece first with your glasses on and then with them off, and see if the glasses restrict the view to only a portion of the full field. If they do, you can easily observe with your glasses off by just refocus- ing the telescope the needed amount.

Aligning the Finder Scope

The ShortTube 80-T comes with a 6x26 correct-image achromatic finder scope. (The 6x means six-times magnifi- cation, and the 26 indicates a 26mm aperture.) The finder scope makes it easier to locate the subject you want to observe in the telescope, because the finder scope has a much wider field of view. Unlike most finder scopes, images viewed in the correct-image finder scope will appear prop- erly oriented (same as the naked eye), which makes finding objects even easier.

Before you use the finder scope, it must be precisely aligned with the telescope, so they both point to exactly the same spot. Alignment is easiest to do in daylight, rather than at night under the stars. First, insert the lowest-power (25mm) eyepiece into the telescope’s focuser. Then point the tele- scope at a discrete object such as the top of a telephone pole or a street sign that is at least a quarter-mile away. Move the telescope so the target object appears in the very center of the field of view when you look into the eyepiece.

Now look through the finder scope. Is the object centered in the finder scope’s field of view, i.e., on the crosshairs? If not, hopefully it will be visible somewhere in the field of view, so only fine adjustment of the two black nylon align- ment screws will be needed. Otherwise you’ll have to make coarser adjustments to the alignment screws to redirect the aim of the finder scope.

Use the two alignment screws to center the object on the crosshairs of the finder scope. Then look again into the telescope’s eyepiece and see if it is still centered there as well. If it isn’t, repeat the entire process, making sure not to move the telescope while adjusting the alignment of the finder scope.

Finder scopes can come out of alignment during trans- port of the telescope, so check the alignment before each observing session.

Focusing the Finder Scope

If, when looking through the finder scope, you notice that the images appear somewhat out of focus, you will need to refocus the finder scope for your eyes. First loosen the lock ring located behind the objective lens cell on the body of the finder scope (see Figure 2a). Back the lock ring off by a few turns, for now. Refocus the finder scope on a distant object by threading the objective lens cell in or out of the finder scope body. Precise focusing will be achieved by focusing the finder scope on a bright star. Once the image appears sharp, retighten the lock ring behind the objective lens cell. The finder scope’s focus should not need to be adjusted again.

Terrestrial Viewing

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

For terrestrial applications, we recommend mounting the ShortTube 80-T on an altazimuth-style camera tripod or telescope mount such as the Orion VersaGo, which allow simple vertical (altitude) and horizontal (azimuth) motions.

Astronomical Viewing

The ShortTube 80-T excels for astronomical observation. Its unobstructed 80mm aperture and short 400mm focal length (f/5) provide bright, expansive views of star fields and celes- tial objects residing within our solar system and beyond.

The ShortTube 80-T can show much more than what is vis- ible on Earth during the day. Once the Sun sets, there are literally thousands of objects in the night sky that can be inspected more closely. For astronomical usage, we recom- mend a 90° star diagonal instead of the 45° correct-image diagonal that comes with the telescope. The correct-image diagonal is designed for daytime use, and will cause some degradation of image quality when used for astronomy. Also, the viewing angle provided by a 90° star diagonal is more comfortable for looking up. When using a star diagonal, the image in the eyepiece will appear backwards (inverted left- to-right).

For casual stargazing, an altazimuth mount mount will do the job just fine. But an equatorial mount is designed to make it easier to manually “track” the motion of celestial objects with just one slow-motion cable. Furthermore, with an equatorial mount you can add an optional motor drive to track the stars automatically—a great convenience.

When selecting a location for nighttime stargazing, make it as far away from city lights as possible. Light-polluted skies greatly reduce what can be seen with the telescope. Also, give your eyes at least 20 minutes to dark-adapt to the night sky. You’ll be surprised at how many more stars you will see! Use a red flashlight to see what you’re doing at the telescope, or to read star charts. Red light will not spoil your dark-adapted night vision as readily as white light will.

To find celestial objects with your telescope, you first need to become reasonably familiar with the night sky. Unless you know how to recognize the constellation Orion, for instance, you won’t have much luck locating the Orion Nebula. A simple planisphere, or star wheel, can be a valuable tool for learning the constellations and seeing which ones are vis- ible in the sky on a given night.

A good star chart or atlas can come in handy for helping locate interesting objects among the dizzying multitude of stars overhead. Except for the Moon and the brighter ­planets, it is pretty time-consuming and frustrating to hunt for objects randomly, without knowing where to look. It is best to have specific targets in mind before you begin look- ing through the eyepiece.

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