Collimating eye piece 1.25″ for refractor telescope. The difference is that it has no lenses, but only a small hole in the center and a large opening on the side. A silver reflective surface can be seen there, which is inclined at 45° to the eyepiece and which also has a small hole in the center.
The eyepiece is inserted into the focus of its refractor, which must be set in such a way that the opening on the side of the collimator is directed at a brightly lit area or light source. The front opening of the refractor must be covered. Now take a look through the little hole in the eyepiece. You will see two reflections, coming from two convex surfaces of the objective lens. Now you need to carefully loosen the screws that hold the front lens in place and tilt the lens so that the two reflection points line up. Then carefully retighten the screws, avoiding as much as possible to change the orientation of the lens again. The telescope is perfectly collimated