Herschel wedge

The trapezoidal prism shape refracts the remainder of the light gathered by the telescope's objective away at an angle.

[1] While they decrease the intensity of the light, they do not affect the visible spectra, resulting in a more accurate spectral profile, which can be filtered to bring out certain details.

[further explanation needed] Hershel Wedges present a unique set of hazards and design considerations for the amateur astronomer.

However, it’s important to remember the majority of this focal plane remains in free space, and when it is allowed to focus unfiltered sunlight, like in the case of a Herschel Wedge telescope, it can have disastrous consequences.

People who have made a habit of inspecting the inside of their telescope by viewing it from the front or even those who simply want to cap it while its outside may not realize that the same action during the day under sunlight will blind them.