#COLLIMATING A REFLECTOR TELESCOPE PROFESSIONAL#

The only disadvantage is that not all nights have good enough seeing (atmospheric steadiness) to ensure that the diffraction rings are centered around the star. Star test: A star test is free, easy, and works with any type of telescope. If not, there’s usually a way to adjust it. If it scribes a straight line, you’re good to go. Turn it on and roll it along a flat surface, projecting the beam on a wall.

(If you do this, be certain their eyes are closed because laser light can harm vision.)īefore using any laser collimator, make sure it’s trued. In a pinch at night, I’ve aimed it at a friend.

It sits in the focuser and shines a beam that ideally reflects onto the hole it came from.īut if the telescope is so far out of collimation that the return beam doesn’t even hit the secondary mirror, it’s useful to point it at a nearby wall to help make the initial adjustments. Laser collimator: Even though a laser collimator has advantages and disadvantages (the optics can be slightly out of alignment and yet look perfect), it’s always been my preferred “quick” method. Many amateurs I know who own reflectors think a Cheshire is the best way to go in terms of proper collimation. Although it’s mainly used to ensure that your secondary mirror is aligned with respect to your focuser, it can also be used to ensure correct alignment of the secondary and primary mirrors.Ĭheshire: This collimator adds a set of crosshairs to a sight tube. Once you get the process down, it takes only a few minutes.Ĭollimation cap: A collimation cap, or sight tube, is a plug that fits in your reflector’s focuser. Fortunately, collimating a reflector is simple. I collimate my observatory-based 18-inch reflector before every session.

#COLLIMATING A REFLECTOR TELESCOPE PROFESSIONAL#

If a Maksutov needs collimation, it’s best to send it to the manufacturer or contact a professional because it’s generally difficult to access and adjust the primary mirror.įinally, reflectors will need frequent collimation - as in, every time you transport it to a different site, and maybe even if you don’t. Unlike an SCT, however, collimating one isn’t easy. Maksutov telescopes - a design like the SCT - tend to hold collimation well. The good news is SCT collimation is easy. Some tend to require frequent collimation others hold it well. If you purchased the scope used and don’t choose to return it to the seller, send it to the manufacturer for adjustment. If that happens, especially for more advanced designs like triplets and Petzvals, I strongly recommend returning it for an exchange. Some, however, may not arrive collimated, most likely due to shocks during transit. A refractor that doesn’t suffer an accident (like a drop) typically won’t need additional collimation over its lifetime. Refractors are factory aligned, and due to their fixed lens, they hold collimation well. Certain designs - reflectors and Schmidt-Cassegrain telescopes, or SCTs - require collimation every time you set up. If the rings aren’t centered, odds are good that the telescope is not collimated correctly. 59 shows these points, along with perfect diffraction rings. Inside focus refers to the eyepiece’s focal point falling inside the light cone it’s the reverse for outside focus. These two non-focused regions are called inside and outside focus. The easiest way to check a telescope’s collimation is to wait until the optics have cooled, pick a bright star, place it in the center of the eyepiece’s field of view, and defocus slightly, first one way, then the other. Further complicating the matter, your telescope could appear to be optically collimated without being mechanically collimated. Mechanical collimation is necessary when the physical components in your scope don’t line up properly - a focuser isn’t square to the tube, a mirror isn’t centered in the tube, or a secondary mirror is misaligned. Optical collimation aligns a telescope’s optical surfaces to bring the image to the correct orientation in the focal plane. There are two types of collimation: optical and mechanical. For simplicity, I’ll talk about the three major types (and one subtype) of telescopes and point out when you need to collimate. All telescopes need to be collimated at some point however, it’s easy to perform this task on some and a bit more involved for others. More than likely it just needs to be collimated.Ĭollimation is the process of aligning all components in a telescope to bring light to its best focus. What’s going on? No matter what you do, you simply can’t get a clear image. You take it out in the backyard, manage to find a few targets, and. You spend an hour or so unpacking and assembling the telescope. You’ve done your research and decided on an 8-inch Dobsonian-mounted reflector, or perhaps a 4-inch refractor, or another model that had a great review. The big day’s here: Your first telescope has arrived.

Collimating a reflector telescope