Celestron 1.25in Erect Image 45degree Diagonal

Celestron 1.25in Erect Image 45degree Diagonal

If you have a refractor or a catadioptric telescope (the Schmidt-Cassegrain is the most popular example but Maksutovs are also compatible), and you would like to use it for terrestrial observations, the most useful additional accessory you can buy is an erect-image diagonal.

This diagonal will also help beginners who find the traditional inverted image given by star diagonals.  This is a useful way to correct the image to its proper orientation.  That makes it easier to find objects, and track them.