StarDikor 1.25 Inch Cheshire Collimating Eyepiece For Newtonian Refractor Telescopes Optical Axis Calibrator Short Version Collimation is the process by which an instruments optical components are brought into precise alignment with its optical axis and mechanical axis. In other words, all the mirrors and/or lenses should be centered and angled so that light entering the telescope forms a sharp image precisely in the center of the eyepiece. If the optics are not properly aligned, stars will appear not as pinpoints as they should, but rather as flared, teardrop-shaped comets or sea gulls. Features: 1.Fits in 1.25 focusers and easy to use;simply cap the telescope, remove the diagonal, and place the eyepiece directly in the focuser. 2.For aligning optics of Newtonian reflectors, Dobsonian reflectors, and Schmidt-Cassegrain Telescopes (SCTs). 3.The collimator for mirror (reflector) telescopes has a 45 degree plate for easier visual accuracy. 4.Item was made by aluminum with crosshair at the bottom allow quick and precise centering of the optics. 5.This collimation eyepiece can be used for precisely collimating the Newtonian and Schmidt-Cassegrain reflector telescopes for better image quality. 6.Accurate collimation is essential for high power observing. Stars will become more like pin points of light, and Planetary / Lunar detail will be enhanced. Purpose of the Collimating Eyepiece Aligning the mirrors seems easy enough, in theory, but in practice it can be difficult without the proper tools. A common way of collimatingthe quick and dirty methodis to simply remove the eyepiece and look down the focuser tube to center the mirror reflections. The accuracy of this method, however, is not reliable. For one thing, there is no way to know whether you are looking straight down the focuser tube; your line of sight could be off by a degree or two. Another problem is knowing when the reflections of the mirrors are exactly centered. Just eyeballing it isnt precise enough; the reflections may appear to be centered when in fact they are not. The Collimating Eyepiece will take care of both of these problems, allowing you to achieve precise collimation without guessing, and thus improve your telescopes performance. The Collimating Eyepiece is a combination of a sight tube and a Cheshire eyepiece. The sight tubes narrow field of view and crosshairs provide a reference for centering the optical elements during the collimation process. A Cheshire eyepiece has a polished flat set in the barrel at a 45 angle, which directs light entering from a cutout in the side of the barrel down into the optical path. The Cheshire allows quick and easy collimation of the primary mirror, assuming the mirror has been marked with a spot exactly in its center. Using the Collimating Eyepiece Collimation can be performed in daylight, when it is easier to see what youre doing. However, never point the telescope or the cutout side of the Collimating Eyepiece at, or anywhere near, the Sun, or serious and instant eye damage could result! Insert the Collimating Eyepiece directly into the 1.25 focuser. When using a 2 focuser, place the Collimating Eyepiece into a 1.25 adapter. If you use a star diagonal with your telescope, as is common for Schmidt-Cassegrain telescopes, remove it before inserting the Collimating Eyepiece. The eyepiece should be inserted to a depth such that the bottom edge of the eyepiece tube appears slightly wider than the outer edge of the secondary mirror when you look through the sight hole. Rotate the eyepiece so that the cutout side is directed toward any available external light. Make sure there is adequate light in the room or outside so that when you look through the sight hole, you can see the edges of the secondary mirror clearly. Tighten the thumbscrew on the focuser tube to secure the Collimating Eyepiece in place. Now, you are ready to proceed with collimation. The Collimating Eyepiece will take care of both of these problems, allowing you to achieve precise collimation without guessing, and thus improve your telescopes performance. The Collimating Eyepiece is a combination of a sight tube and a Cheshire eyepiece. The sight tubes narrow field of view and crosshairs provide a reference for centering the optical elements during the collimation process. A Cheshire eyepiece has a polished flat set in the barrel at a 45 angle, which directs light entering from a cutout in the side of the barrel down into the optical path. The Cheshire allows quick and easy collimation of the primary mirror, assuming the mirror has been marked with a spot exactly in its center. Collimation of Refracting Telescopes If you use the eyepiece for checking the collimation of a refracting (lens) telescope, then you will see as many reflections as there are lenses in the telescope. If all the reflections are round and centred, then your telescope is well collimated. Care and Maintenance Since the