Schmidt-Cassegrain, Maksutov-Cassgegrain and refracting telescopes can also be used for daytime terrestrial use, as well as for astronomy.
However, if you look through your telescope with the standard mirror or star diagonal installed, you will notice that objects may be either upside down, flipped so that you see a mirror image, or a combination of the two. This is fine for observations of celestial objects, but it can be a little confusing when you are trying to track a boat as it moves through the water, or an eagle as it flies towards his perch. Luckily, this is an easy problem to correct – and the most useful additional accessory you can buy is an erect-image diagonal
Simply remove the standard diagonal from the telescope’s focuser or visual back, and install the Celestron 45º Erect Image Diagonal. Now, when you insert an eyepiece, objects will be right side up and left-to-right correct. The 45º angle of this Amici prism diagonal is very comfortable for daytime observations, where the telescope is often in a horizontal position.
Please Note: Adding an erect-image diagonal to a Newtonian reflector will not result in images that are right side up and left-to-right correct. The optical design of a Newtonian will always produce images that are rotationally off in orientation. This does not mean that you can’t use a Newtonian reflector during the day, it just means that you have to get used to objects oriented in unrealistic positions.