Cheshire eyepiece 1.25 "for the adjustment of lens telescopes
Outwardly, it looks at first glance, like a normal eyepiece. The difference is that it has no lenses, but only a small hole in the center and a large opening on the side. There you can see a silver reflective surface which is at a 45 ° angle to the eyepiece, and also has a small hole in the middle. This eyepiece is inserted into the focuser of her refractor, which must be aligned so that the lateral opening looks bright light against a surface or to the light of a lamp. The front opening of the refractor lens is covered. Now look through the little hole in the eyepiece.
You will now see two reflections that result from two convex surfaces of the lens. Now you need to loosen the fastening screws of the front lens and tilt the lens so as to bring to the reflex points to cover. Now be carefully re-tightened the screws, if possible without tilting the lens to it again. Thus, the refractor would be perfectly collimated.
Of course you can also use the Cheshire eyepiece for alignment of Newtonian telescopes.
