Orion 130ST EQ Collimation Cap and Mirror Center Mark, Aligning the Secondary Mirror

drawtube

Reflection of primary mirror clip

b.c.

a.

Figure 8. 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
	d.	e.
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).

tion of the secondary mirror (and your eye) centered in the reflection of the primary mirror, as in Figure 8a. If anything is off-center, proceed with the following collimating procedure.

The Collimation Cap and Mirror Center Mark

Your SpaceProbe 130ST 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 collimating is easy to per- form. Figures 8b through 8e assume you have the collimation cap in place.

In addition to providing the collimation cap, you’ll notice a tiny ring (sticker) in the exact center of the primary mirror. This “center mark” allows you to achieve a very precise col- limation of the primary mirror; you don’t have to guess where the center of the mirror is. You simply adjust the mirror posi- tion (described below) until the reflection of the hole in the collimation 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 tele- scope or the image quality. That might seem counterin- tuitive, but it’s 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 reflec- tions for the time being. The secondary mirror itself should be centered in the focuser drawtube, in the direction parallel to the length of the telescope. If it isn’t, as in Figure 8b, it must be adjusted. Typically, 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 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., on the other side of the secondary mirror) will also be helpful in col- limating the secondary mirror. Using a 2mm Allen wrench, loosen the three small alignment setscrews in the center hub of the 3-vaned spider several turns. Now hold the mirror holder stationary (be careful not to touch the surface of the mirrors), while turning the center screw with a Phillips head screwdriver (Figure 9). 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 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 set screws equally to secure the secondary mirror in that position.

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