| The 1.25" Cheshire tool is the most frequently used telescope collimating tool in the world. It can be used with both reflectors and many refractors. With Newtonian reflectors, it is used for closely collimating the primary mirror, once you’ve set the position and orientation of the diagonal mirror with a sight tube. Its use is almost essential with a fast focal ratio (f/4 to f/5) reflector, as even slight collimation errors in these systems can significantly degrade the image. The Cheshire tool can also be used to collimate the lenses of those refractors that have an adjustable lens cell. The Cheshire tool consists of a tube with a sighting hole at the top and a cutout in the side of the tube containing a reflecting surface set at a very precise 45° angle, The Cheshire tool is primarily designed to be used in daylight, but it can be used in complete darkness (for those times when you can’t set up until late) by shining a red flashlight into the cutout in the side of the tube. The 45° reflecting surface on the inside of the Cheshire tool is not a mirror. It is a plane surface of aluminum, lightly polished until it reflects light evenly, and not harshly as a mirror would. This helps diffuse the light to make the collimation easier to see. The Cheshire tool generally provides accurate enough collimation for visual use and most photographic applications. Some observers even use it alone, in lieu of a sight tube/Cheshire combination, and achieve very acceptable collimation. However, using both tools together will provide a significantly more accurate collimation and better images. For critical visual and photographic applications, using an autocollimator as the final step after sight tube/Cheshire collimation will tweak the telescope collimation to its ultimate accuracy. The autocollimator is not available separately, but only as part of the #4575 three-piece Tectron collimation tube set (consisting of a sight tube, Cheshire tool, and autocollimator). The set also includes a 50-page booklet of detailed instructions and drawings concerning precision collimation using the three tools in the set. If you plan to buy only one tool to collimate your fast focal ratio telescope – the Cheshire tool would be your best choice. Here’s a link to some basic Tectron information concerning collimation and the use of the Cheshire tool.
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