Orion 9786 instruction manual Star-Testing the Telescope, Care & Maintenance, Cleaning Mirrors

Out of collimation Collimated

Figure 8. A star test will determine if the telescope's optics are properly collimated. A defocused view of a bright star through the eyepiece should appear as illustrated on the right if optics are per­ fectly collimated. If the circle is unsymmetrical, as illustrated on the left, the scope needs alignment.

A simple star test will tell you whether the optics are, in fact, accurately aligned.

Star-Testing the Telescope

When it is dark, point the telescope at a bright star and accu­ rately center it in the eyepiece’s field of view. Slowly de-focus the image with the focus knob. If the telescope’s optics are correctly aligned, the expanding disk should be a perfect cir­ cle (Figure 8). If the image is unsymmetrical, the optics are out of alignment. The dark shadow cast by the secondary mir­ ror should appear in the very center of the out-of-focus circle, like the hole in a donut. If the “hole” appears off-center, the optics are out of alignment.

If you try the star test and the bright star you have selected is not accurately centered in the eyepiece, the telescope will appear to need optical alignment, even though the optics may be perfectly collimated. It is critical to keep the star centered, so over time you will need to make slight corrections to the telescope’s position in order to account for the sky’s apparent motion.

Care & Maintenance

If you give your telescope reasonable care, it will last a life­ time. Store it in a clean, dry, dust-free place, safe from rapid changes in temperature and humidity. Do not store the tele­ scope outdoors, although storage in a garage or shed is OK. Small components like eyepieces and other accessories should be kept in a protective box or storage case. Keep the dust cover on the front of the telescope and the dust cap on the focuser drawtube when it is not in use.

Your telescope requires very little mechanical maintenance. The optical tube has a smooth painted finish that is fairly scratch-resistant. If a scratch does appear on the tube, it will not harm the telescope. If you wish, you may apply some auto touch-up paint to the scratch. Smudges on the tube can be wiped off with a soft cloth and household cleaning fluid.

Cleaning Mirrors

You should not have to clean the telescope’s mirrors very often; normally once every year or so is fine. Covering the front opening of the telescope with the dust cover when it is not in use will prevent dust from accumulating on the mirrors.

Keeping the dust cap on the focuser’s 1.25" opening is also a good idea. Improper cleaning can scratch the mirror coatings, so the fewer times you have to clean the mirrors, the better. Small specks of dust or flecks of paint have virtually no effect on the visual performance of the telescope.

The large primary mirror and the elliptical secondary mirror of your telescope are front-surface aluminized and over-coated with hard silicon dioxide, which prevents the aluminum from oxidizing. These coatings normally last through many years of use before requiring re-coating.

To clean the secondary mirror, first remove it from the tele­ scope. Do this by keeping the secondary mirror holder sta­ tionary while completely unthreading the Phillips-head screw in the center hub of the spider vane assembly (see Figure 4). Do not touch the mirror surface when doing this. Be careful, there is a spring between the secondary mirror holder and the Phillips head screw; be sure it does not fall into the opti­ cal tube and onto the primary mirror. Once the Phillips-head screw is unthreaded, the secondary mirror and its holder can be removed from the telescope. Then follow the same pro­ cedure described below for cleaning the primary mirror. The secondary mirror does not need to be removed from its holder for cleaning.

To clean the primary mirror, first carefully remove the mirror cell from the telescope. For the 6" Imaging Reflector, you must completely unthread the four screws on the exterior perimeter of the mirror cell (Figure 9). Then pull the cell away from the tube.You will notice the primary mirror is held in the mirror cell with three clips held by two screws each. Loosen the screws and remove the clips.

You may now remove the primary mirror from its cell. Do not touch the surface of the mirror with your fingers. Lift the mirror carefully by the edges. Set the mirror on a clean soft towel. Fill a clean sink free with room temperature water, a few drops of liquid dishwashing detergent, and if possible, a capfull of

Small Phillips-head screws (4)

Figure 9. To remove the mirror cell from the telescope, the four small Phillips-head screws on the perimeter of the mirror cell must be completely unthreaded.

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