Orion 9786 instruction manual Aligning the Secondary Mirror

drawtube

Reflection of primary mirror clip

a.

Reflective surface	Primary mirror
of collimation	center mark
cap

b.c.

d.e.

Figure 3. 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).

tom. This helps center your eye so collimating is easy to per­ form. Figures 3b through 3e assume you have the collimating cap in place.

In addition to the collimating cap, you’ll notice a small ring label on the exact center of the primary mirror. This “center mark” allows you to achieve a very precise alignment of the primary mirror; you don’t have to guess where the center of the mirror is. You simply adjust the primary mirror position (described below) until the reflection of the hole in the col­ limating cap is centered inside the ring.

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 counter-intuitive, but it’s true!

Aligning the Secondary Mirror

It helps to adjust the secondary mirror in a brightly lit room with the telescope pointed toward a bright surface, such as white paper or wall. Placing a piece of white paper in the telescope tube opposite the focuser (i.e. behind the secondary mirror) will also be helpful in collimating the secondary mirror.

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 isn’t, as in Figure 3b, it must be adjusted. Typically, this adjustment will rarely, if ever, need to be done.

Note:When make adjustments to the secondary mirror position, be careful not to stress the spider vanes, or they may bend.

To adjust the secondary mirror left-to-right in the focuser drawtube, use the included 2.5mm hex key to loosen the three small alignment setscrews in the center hub of the 4-vaned spider several turns. Now hold the mirror holder stationary (be careful not to touch the surface of the mirror), while turn­ ing the center screw with a Phillips head screwdriver (Figure 4). Turning the screw clockwise will move the secondary mir­ ror 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 cen­ tered left-to-right in the focuser drawtube, rotate the second­

Phillips head screwdriver

Figure 4. 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.

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