Orion 9738 Collimation Cap and Mirror Center Mark, Aligning the Secondary Mirror

To check collimation, remove the eyepiece and look down the focuser drawtube. You should see the secondary mirror cen- tered in the drawtube, as well as the reflection of the primary mirror centered in the secondary mirror, and the reflection of the secondary mirror (and your eye) centered in the reflection of the primary mirror, as in Figure 14a. If anything is off-cen- ter, as in Figure 14b, proceed with the following collimation procedure.

Note About the Collimatable 2" Focuser

The SkyView Pro 8’s 2" focuser can be collimated by 3 pairs of push-pull screws located on the ring at the base of the focus- er (Figure 4). The focuser was collimated at the factory and should never need to be adjusted. Focuser collimation is only required under very rare circumstances but has been made available for this telescope should such a need arise.

The Collimation Cap and Mirror Center Mark

Your SkyView Pro 8 EQ comes with a collimation cap. This is a simple cap that fits on the focuser drawtube like a dust cap, but has a hole in the center and a silver bottom. This helps center your eye so that collimation is easy to perform. Figures 14b through 14e assume you have the collimation cap in place.

In addition to the collimation cap, the primary mirror is marked with a circle at its exact center. This “center mark” allows you to achieve a precise collimation of the primary mirror; you don’t have to guess where the center of the mirror is. You simply adjust the mirror position (described below) until the reflec- tion of the hole in the collimation cap is centered in the ring. The center mark is also required for best results when using other collimating devices, such as Orion’s LaserMate Laser Collimator, obviating the need to remove the primary mirror and mark it yourself.

Note: The center ring sticker need not ever be removed from the primary mirror. Because it lies directly in the shadow of the secondary mirror, its presence in no way adversely affects the optical performance of the telescope or the image quality. That might seem counterintuitive, but its true!

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 14b, 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 telescope tube opposite the focuser (in other words, on the other side of the secondary mirror) will also be helpful in col- limating the secondary mirror. Using a 2mm hex key, loosen the three small alignment set screws in the center hub of the 4-vaned spider several turns. Now keep the mirror’s holder stationary (be careful not to touch the surface of the mirrors),

while turning the center screw with a Phillips head screwdriver (See Figure 15). Turning the screw clockwise will move the secondary mirror toward the front opening of the optical tube, while turning the screw counter-clockwise will move the sec- ondary mirror toward the primary mirror.

Note: When making these adjustments, be careful not to stress the spider vanes or they may bend.

Figure 15. To center the secondary mirror under the focuser, hold the secondary mirror holder in place with one hand while adjusting the center bolt with a Phillips screwdriver. Do not touch the mirror’s surface!

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 14c, you will need to adjust the tilt of the secondary mirror. This is done by alternately loosen- ing one of the three alignment set screws while tightening the other two, as depicted in Figure 16. The goal is to center the primary mirror reflection in the secondary mirror, as in Figure 14d. Don’t worry that the reflection of the secondary mirror (the smallest circle, with the collimation cap “dot” in the center) is off-center. You will fix that in the next step.

Figure 16. Adjust the tilt of the secondary mirror by loosening or tightening the three alignment set screws with a 2mm hex key.

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