Orion 9826 Setting Up and Using the Equatorial Mount, Focusing the Telescope, Polar Alignment

The telescope is now balanced on the R.A. axis. It is not nec- essary to balance the telescope on the Dec. axis, since the optical tube’s mounting plate is positioned so that the tele- scope will automatically be balanced on that axis. When you loosen the lock lever on one or both axes of motion and man- ually point the telescope, it should move without resistance and should not drift from where you point it.

Focusing the Telescope

Point the telescope so the front end is aimed in the general direction of an object at least 1/4-mile away. With your fingers, slowly rotate the focusing knob until the object comes into sharp focus. Go a little bit beyond sharp focus until the image just starts to blur again, then reverse the rotation of the knob, just to make sure you’ve hit the exact focus point.

If you have trouble focusing, rotate the focus knob counter- clockwise as far as it will go. Look through the eyepiece while slowly rotating the focus knob clockwise.You should soon see the point at which focus is reached.

Do You Wear Eyeglasses?

If you wear eyeglasses, you may be able to keep them on while you observe. In order to do this, your eyepiece must have enough “eye relief” to allow you to see the entire field of view with glasses on. You can try this 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 the glasses do restrict the field of view, you may be able to observe with your glasses off by just refocusing the telescope the needed amount.

If your eyes are astigmatic, images will probably appear the best with glasses on. This is because a telescope’s focuser can accommodate for nearsightedness or farsightedness, but not astigmatism. If you have to wear your glasses while observing and cannot see the entire field of view, you may want to purchase additional eyepieces that have longer eye relief.

Aligning the Finder Scope

The finder scope must be aligned accurately with the tele- scope for proper use. To align it, aim the main telescope in the general direction of an object at least 1/4-mile away, such as the top of a telephone pole, a chimney, etc. Do this by first loosening the R.A. and Dec. lock levers. Position the telescope so the object appears in the eyepiece’s field of view and then retighten the R.A. and Dec. lock levers. Use the slow-motion control cables to center the object in the eyepiece.

Now, look in the finder scope. Is the object visible? Ideally, it will be somewhere in the finder’s field of view. If it is not, some coarse adjustments of the two black nylon finder scope align- ment thumb screws will be needed to get the finder scope roughly parallel to the main tube.

Note: The image in the telescope’s eyepiece will appear inverted from left-to-right (mirror reversed), which is nor- mal for telescopes that utilize a star diagonal. The image in the finder scope is oriented the same as the naked eye.

By loosening or tightening the alignment thumbscrews, you change the line of sight of the finder scope. Continue making adjustments to the alignment thumbscrews until the image in both the finder scope and the telescope’s eyepiece is exactly centered. Check the alignment by moving the telescope to another object and fixing the finder scope’s crosshairs on the exact point you want to look at. Then look through the tele- scope’s eyepiece to see if that point is centered in the field of view. If it is, the job is done. If not, make the necessary adjust- ments until the two images are centered simultaneously.

The finder scope alignment needs to be checked before every observing session. This can easily be done at night, before viewing through the telescope. Choose any bright star or planet, center the object in the telescope eyepiece, and then adjust the finder scope’s alignment thumbscrews until the star or planet is also centered on the finder’s crosshairs. The finder scope is an invaluable tool for locating objects in the night sky; its usage for this purpose will be discussed later, in detail.

Focusing the Finder Scope

If, when looking through the finder scope, the images appear somewhat out of focus, you will need to refocus the finder scope for your eyes. Loosen the lock ring located behind the objective lens cell on the body of the finder scope (see Figure 3a). 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 on 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.

5.Setting Up and Using the Equatorial Mount

When you look at the night sky, you no doubt have noticed that the stars appear to move slowly from east to west over time. That apparent motion is caused by the Earth’s rotation (from west to east). An equatorial mount (Figure 6) is designed to compensate for that motion, allowing you to easily “track” the movement of astronomical objects, thereby keeping them from drifting out of the telescope’s field of view while you’re observing.

This is accomplished by slowly rotating the telescope on its right ascension (R.A.) axis, using only the R.A. slow-motion cable. But first the R.A. axis of the mount must be aligned with the Earth’s rotational (polar) axis—a process called polar alignment.

Polar Alignment

For Northern Hemisphere observers, approximate polar align- ment is achieved by pointing the mount’s R.A. axis at the North Star, or Polaris. It lies within 1° of the north celestial pole (NCP), which is an extension of the Earth’s rotational axis out into space. Stars in the Northern Hemisphere appear to revolve around the NCP.

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