Orion 102mm EQ Focusing the Telescope, Do You Wear Eyeglasses?, Aligning the Finder Scope

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 block is positioned so that the tele- scope will automatically be balanced on that axis. Now when you loosen the lock knob on one or both axes of motion and manually point the telescope, it should move without resist- ance and should not drift from where you point it.

a.

b.

Figure 4a, b. Proper operation of the equatorial mount requires balancing the telescope tube on the R.A. axis.

(a)With the R.A. lock knob released, slide the counterweight along the counterweight shaft until it just counterbalances the tube. (b) When you let go with both hands, the tube should not drift up or down.

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. Now, 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 starts to blur again, then reverse the rotation of the knob, just to make sure you’ve hit the exact focus point. You will have to readjust the focus when aiming at subjects of varying distance, or after changing eyepieces.

If you have trouble focusing, rotate the focus knob counter- clockwise as far as it will go. Now 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, to 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 refocusing the tele- scope the needed amount.

If your eyes are astigmatic, images will probably appear 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 observ- ing 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 knobs. Position the telescope so the object appears in the eyepiece’s field of view and then retighten the R.A. and Dec. lock knobs. 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 thumb screws, you change the line of sight of the finder scope. Continue making adjustments to the alignment thumb screws 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 match up.

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 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, in detail.

6