a.
b.c.
d.e.
Figure 10. Collimating the optics. (a) When the mirrors are properly aligned, the view down 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 correctly aligned, the “dot” will be centered, as in (e).
Aligning the Secondary Mirror
With the collimation cap in place, look through the hole in the cap at the secondary (diagonal) mirror. Ignore the reflections for the time being. The secondary mirror itself should be cen- tered in the focuser drawtube, in the direction parallel to the length of the telescope. If it isn’t, as in Figure 10b, it must be adjusted. This adjustment will rarely, if ever need to be done.
It helps to adjust the secondary mirror in a brightly lit room with the telescope pointed towards a bright surface, such as white
paper or wall. Also placing a piece of white paper in the tele- scope tube opposite the focuser (in other words, on the other side of the secondary mirror) will also be helpful in collimating the secondary mirror. Using a 2mm hex key, loosen the three small alignment set screws in the center hub of the
Figure 11. To center the secondary mirror under the focuser, hold the secondary mirror holder in place with your fingers while adjusting the center screw with the Phillips head screwdriver. Do not touch the mirror’s surface.
Note: When making these adjustments, be careful not to stress the spider vanes or they may bend.
When the secondary mirror is centered in the focuser draw- tube, rotate the secondary mirror holder until the reflection of the primary mirror is as centered in the secondary mirror as possible. It may not be perfectly centered, but that is OK. Now tighten the three small alignment screws equally to secure the secondary mirror in that position.
If the entire primary mirror reflection is not visible in the sec- ondary mirror, as in Figure 10c; you will need to adjust the tilt of the secondary mirror. This is done by alternately loosening one of the three alignment set screws while tightening the other two, as depicted in Figure 12. The goal is to center the primary mirror reflection in the secondary mirror, as in figure 10d. Don’t worry that the reflection of the secondary mirror (the smallest circle, with the collimation cap “dot” in the cen- ter) is
Alignment set screws (3) |
|
|
| Figure 12. | |
|
| Adjust the tilt of |
|
| the secondary |
|
| mirror by |
|
| loosening or |
|
| tightening the |
|
| three alignment |
|
| set screws with a |
|
| 2mm hex key. |
|
|
|
10
