Just tried this CLS filter on ETA CARINAE NEBULA low down on the horizon.
With a big waxing moon to spoil things.Using just a 20mm plossl, 10" sct.
Im able to make out the keyhole.Not great under these conditions, but there it is. Absolutely INVISIBLE without the filter.
Same with planetary ngc3918 in Centuarus.
Bty.This makes a great Lunar and planetary filter, on all kinds of scopes, Ive found.
.PS: Put this one on your list. Cheers bigjoe.