Collimating Eyepiece for Newtonian Telescopes, Long Collimator
This collimating eyepiece (collimator) is for 31.7mm, 1.25” focusers.
It is similar to the Cheshire-type, but in addition it is equipped with a crosshair.
The collimating eyepiece has a shiny metallic, sloping ( under 45 ) surface with a hole in the middle.
Through the hole you can see through to the front lense.
As it is more practical to use it in daytime, please leave the lens cover on to make sure that the reflection could be seen.
When looking through the hole, the sloping, shiny surface will be seen as a shiny circle in the middle.
In the case of a well collimated refractor there will be two reflections, which lie on the top of each other, and are centred in the middle of the picture.