GSO
GSO Moon Filter 13pct 1.25-inch
From$11.95
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05The numbers
What These Numbers Mean
TransmissionND 0.9
13 percent
It passes about one eighth of the light and blocks the rest evenly across the spectrum. On a bright gibbous Moon in a six-inch or larger telescope that is the difference between squinting and comfortably studying craters.
What changesComfort
Glare, not detail
The filter does not add resolution. What it does is stop the Moon from dazzling you, which lets your eye settle and pick out subtle contrast along the terminator, and preserves your dark adaptation for the rest of the session.
ColourNeutral
Neutral density
A neutral coating dims everything equally rather than tinting the view green or grey the way cheap coloured moon filters do. The Moon still looks like the Moon.
Barrel sizeStandard
1.25 inch
Threads into the standard eyepiece size, so it works with almost any telescope out of the box and costs less than most eyepiece accessories.
When it is too muchSituational
Small scopes, thin crescents
In a small telescope, or on a crescent Moon, 13 percent transmission can leave the view dimmer than you want. A variable polarising filter suits observers who want to tune the amount of dimming.