Variable polarizing filters are one of the best filters you can have for a telescope. They are used to cut down the glare from the moon and bright planets like Venus, Jupiter and Mars, allowing more detail to be seen. The filters are adjustable by rotating to change the amount of light allowed through, perfect for tuning for a crescent moon versus full moon, for example. These 1.25" filters thread into the bottom barrel of a 1.25" eyepiece. A protective plastic storage case is included.