Orion 9527 Preparing the Telescope for Collimating, Aligning the Secondary Mirror

Figure 11. Placing a piece of white paper inside the optical tube opposite the focuser provides a bright background when viewing into the focuser.

Figure 12. To center the secondary mirror axially under the focuser, hold the secondary mirror holder in place with your fingers while adjusting the center screw with a large Phillips-head screwdriver. Later you will adjust the tilt of the secondary mirror by turning the three small set screws that surround the large center screw.

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 tele­ scope or the image quality. That might seem counter­ intuitive, but it’s true!

Preparing the Telescope for Collimating

Once you get the hang of collimating, you will be able to do it quickly even in the dark. For now, it is best to collimate in daylight, preferably in a brightly lit room and aimed at a light- colored wall. It is recommended that the telescope tube be oriented horizontally. This will prevent any parts from the secondary mirror from falling down onto the primary mirror and causing damage if something comes loose while you are making adjustments. Place a sheet of white paper inside the optical tube directly opposite the focuser (Figure 11). The paper will provide a bright “background” when viewing into the focuser. Just be sure to remove the paper when you’re finished collimating.

Aligning the Secondary Mirror

To adjust the secondary mirror collimation, you will need both a small and a large Phillips screwdriver.

You will need to check, and adjust if necessary, four aspects of the secondary mirror’s alignment:

1.The secondary mirror’s axial position

2.The secondary mirror’s radial position

3.The secondary mirror’s rotational position

4.The secondary mirror’s tilt

The first three will probably only need to be checked and (pos- sibly) adjusted once. Thereafter, it is usually only the second- ary mirror’s tilt that will need to be adjusted occasionally.

Adjusting the Secondary Mirror’s Axial Position

With the collimating 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. If it is off-center along the axis of the telescope, i.e., positioned too far toward the front open- ing or toward the rear of the telescope, as it is in Figure 9b, you will have to adjust the mirror’s axial position.

To do so, use a small Phillips screwdriver to loosen the three small alignment set screws in the center hub of the 4-vane spider several turns. Now, grasp the mirror holder (the cylinder that is attached to the back of the secondary mirror itself) with one hand while turning the center screw with a large Phillips head screwdriver with your other hand (Figure 12). 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 secondary mirror toward the primary mirror. When the secondary mirror is centered axially in the focuser drawtube, 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 cen- tered, but that is fine for now. Then, tighten the three small alignment set screws equally to secure the secondary mirror in that position.

Adjusting the Secondary Mirror’s Radial Position

Like the axial position, the secondary mirror’s radial position was set at the factory and will probably not need any adjust- ing, or if it does, you’ll typically need to do it only once.

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