Cheshire collimators, also known as collimation caps, are a must-have for any owner of a Newtonian reflecting telescope. They’re fairly inexpensive and, on their own, are adequate for the alignment of slower instruments. For faster telescopes, they are best used in conjunction with a laser collimator and/or the star test.
Advantages & Disadvantages of Cheshire Collimators
Collimation caps and Cheshires are terms that refer to basically the same thing, relying on a cylindrical device that inserts into your focuser with a reflective surface on the opposite side and a small pinhole. You may hear the term “Cheshire” used to refer to a Cheshire “combination tool” that adds additional features, but the basic “Cheshire” design is just any collimation cap with a reflective interior. This may cause a little confusion when shopping.
Most of the things marketed as “Cheshires”—in fact, combination tools—usually add a 45-degree angled window and crosshairs. These are not particularly necessary and may or may not help you when collimating. However, some people like to have them or even have both a simple “cap” and a combination tool/sight tube. Crosshairs will allow you to have better accuracy in alignment if your primary mirror is center-dotted, but they definitely aren’t always necessary, and some people find them to be more of a hindrance than a help.
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. However, they 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, and there is truthfully only so much you can do. As such, they will probably need to be supplemented by a laser collimator or collimating on a star in those instruments.
A Cheshire collimation tool is not particularly useful for collimation with a typical catadioptric, Cassegrain, or Ritchey-Chretien telescope. You will need a laser collimator and/or have to collimate these telescopes on stars.
Best Cheshire Collimators: Our Recommendations
Crosshairs are nice to have but are not strictly needed for a good collimation tool. The same goes for a long barrel; long barrels can help if you are using a very slow f/ratio telescope but may actually be a hindrance with a faster instrument as they can block part of the secondary mirror from view. The most important aspects of a good Cheshire collimator or combination tool are all based on machining accuracy. The better the quality control and tolerances, the more centered everything will be—both the hole in the Cheshire and the body of it in your focuser. This means that the best collimation tools will always be the most expensive, and the lower-priced ones will compromise on accuracy.
1. Best Value Cheshire – Farpoint Cheshire Collimator
The Farpoint Cheshire (available in 2” diameter and 1.25” diameter formats) is actually a collimation cap given its lack of crosshairs, but is made to extremely high accuracy and fits perfectly in any focuser. The tight machining tolerances and well-made reflective inside face make this great for collimating even fairly fast telescopes without much difficulty.
Tip: For this item, most of the time, Agena is cheaper and has the item in stock.
2. Astro Systems Lite Pipe
The AstroSystems LitePipe is a combination tool ideal for aligning both your primary and secondary mirrors and uses a long, 1.25” barrel with precision crosshairs in it. It is best used with something like a Howie Glatter Parallizer adapter if you are using a 2” focuser with your telescope to guarantee centering accuracy, however.
3. Best Budget Cheshire Collimator: SVBONY SV197 Cheshire Collimator
The SVBONY SV197 Cheshire Collimator is similar in design to the LitePipe but not quite as accurate. It does, however, include a 45-degree tilted viewing window. It is a good budget option and works well with most telescopes. The only concern is that the long barrel has no mechanical stop and may hit the secondary mirror in smaller instruments if you are not careful and slide it all the way into your focuser.
4. Cheapest Recommended Cheshire – Rigel Systems Aline
The Rigel Systems Aline (available in both 2” diameter and 1.25” diameter) is an extremely simple collimation cap. It’s really not 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 and is a bit better than just making one yourself out of a film canister thanks to its reflective inside face.