Orion 5684 instruction manual Adjusting the Tilt of the Primary Mirror, Star-Testing the Telescope

primary mirror itself; this is the laser beam being reflected from the secondary mirror off the surface of the primary mirror. The red spot should be centered on the primary mir- ror’s surface. If it isn’t, adjustments will be need to be made to the secondary mirror’s tilt. This is done with the secondary mirror colli- mation screws, usually located on the central hub of the telescope’s spider vane assembly. In the case of Orion reflectors there are three recessed 2mm Allen screws surrounding the center Phillips-head screw. Do not loosen this center screw. The Allen screws work on a push-pull basis, loosen one and tighten anoth- er until you achieve the correct position of the laser in the target. Make sure all three screws are firmly tightened against the mirror holder upon completion to ensure the mirror holds its position. Consult the owners manual of your telescope for instructions pertaining to other optical tubes.

Make minor adjustments to the telescope’s secondary mirror collimation screws until the reflection of the laser beam is centered on the primary mirror. If your primary mirror is center marked the red spot should fall directly in the center of the collimation target.

Adjusting the Tilt of the Primary Mirror

Laser spot

on primary mirror

Before

After

Figure 9a, 9b. To center the red laser spot on the primary mirror, you will need to adjust the tilt of the secondary mirror.

Primary mirror center mark

drawtube

Reflection of primary mirror clip

b.

a.

Figure 10. Collimating the optics. (a) When
the mirrors are properly aligned, the view down	c.
the focuser drawtube should look like this (b) With
the collimation cap in place, if the optics are out of
alignment, the view might look something like this.

(c)Here, the secondary mirror is centered under the focuser, but it needs to be adjusted (tilted) so that the

entire primary mirror is visible. (d) The secondary mirror is correctly aligned, but the primary mirror still needs adjustment. When the primary mirror is

The final collimation adjustment is to adjust the tilt of the primary mirror. Remove the laser and use the sight tube eyepiece to complete this step. It may be help- ful to have someone looking through the eyepiece while another person makes adjustments to the collimation screws on the back of the telescope. Otherwise you will need to make minor adjustments at the back of the telescope and check them through the peephole sight tube eyepiece at the front. This does not affect accuracy but the process will take a little bit longer.

The primary mirror will need adjustment if, as in Figure 10d, the secondary mirror is centered under the focuser and the reflection of the primary mirror is centered in the secondary mirror, but the small reflection of the secondary mirror (with the “dot” of the peephole sight tube eyepiece) is off-center. Consult your telescope’s manual for information regarding specific collimation adjustments.

Now, try tightening or loosening one of the collimation thumbscrews with your fingers. Look into the focuser and see if the secondary mirror reflection is at the the center of the primary. You can tell this easily with the sight tube and mirror center mark by simply watching to see if the “dot” is moving closer or farther away

correctly aligned, the “dot” will be centered, as in (e).

from the ring on the center of the primary mir-

ror. When you have the dot centered as much d. as possible in the ring, your primary mirror is collimated. The view through the sight tube should resemble Figure 10e. An optional star

test is the most accurate method to determine

if your optics are accurately collimated­ .

Star-Testing the Telescope
When it is dark, point the telescope at a bright
star and accurately center it in the eyepiece’s
field of view. Slowly de-focus the image with the
focusing knob. If the telescope is correctly col-	e.
limated, the expanding disk should be a perfect

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