In order to enjoy your observing sessions to the fullest, a wide range of accessories have been developed so that you, the observer, can select which ones suit your needs.
Lets start out with diagonals, or star prisms as they are sometimes referred to.
The star diagonals are designed for deep sky observing. These diagonals come in two types. I like the correct-image diagonals because they will reveal the same image at the eyepiece, which is shown in the star atlases. This makes tracking down your target much easier. There is one other kind of prism that is offered, and that is the porro prism.