Product Description ------------------- The Earth’s Moon is the most popular object to observe with a telescope. It’s an obvious target that’s easy to locate and full of exciting geographical features to explore. The Celestron Moon filter enhances lunar viewing by cutting down on the Moon’s bright glare, improving contrast and making faint details easier to observe. Most amateur astronomers keep a Moon filter on hand as an essential part of their observing kit because it provides a more comfortable view and reduces eye fatigue. But a Moon filter isn’t just for the Moon; it also boosts contrasts when viewing deep-sky objects from a light polluted areas. And for terrestrial observers, the Moon filter offers to take down the brightness when viewing land-based targets around sand and snow. The Celestron Moon Filter simply screws onto the insert barrel of most 1.25” eyepieces and can stack with other 1.25” filters. Manufacturer's Description -------------------------- Celestrons Moon Filters are economical eyepiece filters for reducing the brightness of the moon and improving contrast, so greater detail can be observed on the lunar surface. The clear aperture is 21mm for the 31.7mm filter. Transmission is about 18%