Review on Celestron Erect Image Prism: Enhance Clarity for Refractor and Schmidt Cassegrain Telescopes by Brad Cash

I have a Celestron CPC 800 XLT. I used to only use single eyepieces, and when viewing the moon, sun (with solar filter) and planets, it annoyed me that the direction switched from left to right. So I liked to view these objects as my eye would see them through binoculars. I noticed that looking at the stars removes a "notch" of the light in the lower left of the image. As others have said, this device is best used for terrestrial observation or for observing the planets, sun and moon. Note that this is not a 90 degree viewing angle. As a result, for some views it can be a little awkward to see an object without leaning in more than when you're on a 90-degree diagonal.