Cheshire collimators, also known as collimation caps, are a must-have for any owner of a Newtonian-reflecting telescope and I use them all the time. They’re fairly inexpensive and, on their own, are adequate for the alignment of slower focal ratio instruments (>f/5). For faster telescopes, I use them in conjunction with a laser collimator and/or the star test.
Why Do I Say Collimation Caps Are Also Cheshires?
I say so because collimation caps and Cheshires are terms that refer to basically the same thing, relying on a cylindrical device that inserts into our focuser with a small pinhole to look through and a reflective surface on its back side.
You may hear the term “Cheshire” being used only to refer to a Cheshire “combination tool” that adds additional features such as a 45-degree angled window and/or crosshairs to the basic “Cheshire” design, which is just any collimation cap with a reflective interior. I’ve personally noticed this causes a little confusion when people unfamiliar with this shops for “Cheshire.”
I don’t consider these additional features that come with the Cheshire combination tool to be particularly necessary. Sometimes they help me when collimating, sometimes they don’t.
Crosshairs helps me get better accuracy in alignment if my primary mirror is center-dotted, but they definitely aren’t always necessary. I’ve sometimes found them to be more of a hindrance than a help.
The same goes for long barrels. Long barrels can help if I’m using a very slow f/ratio telescope but it is actually a hindrance with a faster instrument as they block part of the secondary mirror from my view.
However, I agree that some people like to have a combination tool or have them as a compliment to a simple “collimation cap” that they already own.
Occasions When Cheshire Doesn’t Help Me Well
Cheshires are of limited accuracy in aligning the primary mirror in faster f/ratio telescopes, as the shadow of the secondary mirror appearing slightly decentered is not as noticeable. Frankly, there is truthfully only so much I can do about it. As such, when I’m using fast instruments, I supplement Cheshires with a laser collimator or by collimating on a star.
I also never found the Cheshire collimation tool to be particularly useful for collimation with a typical catadioptric, Cassegrain, or Ritchey-Chretien telescope. I need a laser collimator and/or have to collimate these types of telescopes on stars.
Reasons Why You May Use Cheshires
Cheshire collimators are cheaper than a laser and may be the only collimation tool you need, especially if you’re a beginner and/or primarily use smaller telescopes. They are not heavy or as sensitive to mechanical misalignment, and thus they work well even in focusers that are plastic or otherwise have fairly low stiffness and lots of play or wobble in them.
Cheshire collimators are also extremely good for checking for any misalignment of your secondary mirror. The human eye has no trouble picking up the de-centering of the secondary mirror in a Cheshire.
Cheshire Collimators That I’ve Used and Can Recommend
The most important aspects of a good Cheshire collimator or combination tool are all based on machining accuracy. I’ve noticed that better the quality control and tolerances of the Cheshires, the more centered everything is—both the hole in the Cheshire and the body of it in the focuser.
Unfortunately, this means that the best collimation tools will always be the most expensive, and the lower-priced ones will compromise on accuracy.
I Got The Best Experience from FarPoint Cheshire
The Farpoint Cheshire (available in 2” diameter and 1.25” diameter formats; I’ve the 2″ format since I use 2″ eyepieces the most) is actually a collimation cap given its lack of crosshairs, but is made to extremely high accuracy and fits perfectly in any of my focusers. I’ve even collimated many of my fairly fast telescopes without much difficulty due to its tight machining tolerances and well-made reflective inside face.
Astro Systems Lite Pipe Is The Best I’ve Used That Have Cross Hairs
The AstroSystems LitePipe is a combination tool that uses a long, 1.25” barrel with precision crosshairs in it. However, if I’m using any of my telescopes with a 2″ focuser, I use something like a pricey Howie Glatter Parallizer adapter to guarantee centering accuracy.
The Chinese Brand SVBony Did Good for Its Price
The SVBONY SV197 Cheshire Collimator is similar in design to the LitePipe but wasn’t quite as accurate when I used it. It does, however, include a 45-degree tilted viewing window. I consider it to be a good budget option and it works well with most of my telescopes.
The only concern I’ve is that the long barrel has no mechanical stop. If I’m not careful and slide the collimator all the way into the focuser, it can hit the secondary mirror in some of my smaller telescopes.
For just $10, Rigel Systems Aline Is The Best I Could Find & Use, And I Don’t Regret It
The Rigel Systems Aline (available in both 2” diameter and 1.25” diameter) is an extremely simple collimation cap. I believe this would be a bit better than just making one yourself out of a film canister thanks to its reflective inside face.
I don’t agree with Rigel’s claim that it’s adequate for a fast reflector on its own, but for a small telescope or as a cheap supplement to a nice laser collimator, this inexpensive tool does the job quite nicely.
