Orion #27183 XT8I Focusing the Telescope, Viewing with Eyeglasses, Aligning the Finder Scope

Focusing the Telescope

With the 25mm Sirius Plössl eyepiece in the focuser and secured with the thumbscrew(s), move the telescope so the front (open) end is pointing in the general direction of an object at least 1/4-mile away. Now, with your fingers, slowly rotate one of the focusing knobs 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 focusing knob so the drawtube is in as far as it will go. Now look through the eyepiece while slowly rotating the focusing knob in the opposite direction. You should soon see the point at which focus is reached.

For XT8i, XT10i and XT12i models, the focus lock thumb screw on the bottom of the focuser body (Figure 13a) will lock the focuser drawtube in place once the telescope is prop- erly focused. The XT6i’s focus lock thumb screw is located on the top of the focuser body (Figure 13b). Before focusing, remember to first loosen the focus lock thumb screw. Do not loosen the thumb screw too much as there must be some ten- sion to keep the drawtube secure within the focuser.

If you find the drawtube tension when focusing is either too tight (focus knob is difficult to turn) or too loose (image shifts when focusing or drawtube moves inward by itself), the ten- sion can be adjusted for optimal performance. On the XT8i, XT10i, and XT12i, the focusing tension adjustment set screw is a 3mm socket head set screw located below the focus lock thumb screw (Figure 13a). A 3mm hex key is required for adjustment of focus tension. On the XT6i, the focusing ten- sion adjustment set screws are the two small set screws located on either side of the focus lock thumb screw (Figure 13b). A 1.5mm hex key is required to adjust the focus tension on the XT6i. Due to the rack-and-pinion focuser design on the XT6, tension adjustment should not normally be needed as it has been pre-adjusted at the factory.

Viewing with 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 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 they do, you can easily observe with your glasses off by just refocusing the telescope the needed amount. If you suffer from severe astigmatism, however, you may find images noticeably sharper with your glasses on.

Aligning the Finder Scope

The finder scope must be aligned accurately with the tele- scope for proper use. To align it, first aim the main telescope in the general direction of an object at least 1/4-mile away, e.g., the top of a telephone pole, a chimney, etc. Position that object in the center of the telescope’s eyepiece.

The finder scope uses a spring-loaded bracket that makes alignment of the finderscope very easy. As you turn either

Naked-eye view

View through telescope

Figure 16. The view through a reflector telescope is upside down. This is true for the SkyQuest XT IntelliScope.

of the thumbscrews, the spring in the bracket’s tensioning pin moves in and out to keep the finder scope secure in the bracket.

Note: The image in the main telescope will appear upside-down (rotated 180°). This is normal for reflector telescopes (see Figure 16).

Now look through the finder scope. Ideally, the object should be within the field of view. If not, then coarse adjustments to the alignment thumbscrews will be needed. Once the image is in the finder scope’s field of view, you will now use the align- ment thumbscrews to center the object on the intersection of the crosshairs. By loosening one alignment thumbscrew, 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 are 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 telescope’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 adjustments until the two images match up.

The finder scope alignment should 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 thumb screws 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.

Focusing the Finder Scope

The finder scope with your SkyQuest IntelliScope has adjust- able focus. If the images in the finder appear somewhat out

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