So I've heard mention of Cheshire eyepieces, sight tubes, and collimation caps for collimating the mirrors in a reflector telescope. During a bit of research I've seen that what some mean by Cheshire is actually the longer sight tube/Cheshire combo tool. When I see JUST a Cheshire it seems to be a shorter eyepiece with a hole in the center and what I'm assuming is a reflective area on the inside. Is a Cheshire just a collimation cap with a mirror in it, or are they the same thing? What is the difference between a Cheshire and the Cheshire/sight tube combo tool?
Could someone please explain the differences between these tools and any other common collimation tools?
In the near future I plan on buying a reflector for my first scope, so I would like to be as well versed in collimation as possible!
Sorry for the noob question, thanks in advance!
THE TOOLS OF COLLIMATION
The most commonly used (there are other exotic, do-it-yourself tools that also work, but they are uncommon) Newtonian collimation tools are:
1. Collimation cap (A simple peep-hole, though not good enough for scopes below f/10. I don’t recommend these except, perhaps, as a quick check to see if the optical elements are at least in gross alignment at the start). It is used solely for primary mirror tilt adjustment.
2. Laser collimator (not useful unless perfectly collimated itself, possessed of a small beam diameter, and not accurate enough for primary mirror collimation unless used with a Barlow lens, but quite useful in the dark. Mfrs.: Glatter, FarPoint, Astrosystems, etc. Used for focuser axis alignment (usually referred to as secondary mirror tilt adjustment).
3. Sight Tube (Cylinder with peep hole at one end and crosshairs at the other. Tectron (1.25”), Catseye (2”). Tectron is no longer in business, but the tools are common in the used market. Combination tools contain this tool).
4. Cheshire (Cylinder with interior annular reflective white surface and blackened center area, producing a reflection from the primary mirror that appears as a bright ring with a dark center. Tectron, Catseye. Combination tools contain this tool).
5. Autocollimator (Cylinder with a reflective mirror inside the peep-hole cap. The internal mirror is perpendicular to the optical axis of the focuser. It produces multiple reflections of the primary mirror’s center marking. Catseye, Tectron, Farpoint, and others).
6. Combination Sight Tube/Cheshire (least expensive, but a little harder to use. It combines the crosshairs of the sight tube and the reflective interior surface of the Cheshire. There are many inexpensive models in the market, and a couple better ones: 1.25” and 2" from AstroSystems called the Light Pipe/Sight Tube, and a 2” from Catseye called the TeleCat).
Collimation is 3 to 4 steps:
--centering the secondary under the focuser--use a sight tube or holographic display laser
--aligning the focuser axis by secondary mirror adjustment--use a sight tube, laser, or combination tool
--aligning the primary mirror axis--use a collimation cap, Cheshire, or barlowed laser, or Krupa collimator.
--(optional) eliminating residual errors--use an autocollimator.
Send me your email address in a private message, and I'll send you a couple collimation tutorials--one simple and one more detailed. Both are illustrated.
Edited by Starman1, 14 January 2020 - 01:49 PM.