Are polarizing filters for viewing the moon? If so, would it be wiser to get one over the ND?
-Mike
-Mike
Polarizing vs. Neutral Density filter
Started by mkawada, 07/27/2002 10:26AM
Posted 07/27/2002 10:26AM
Opening Post
Posted 07/27/2002 01:03PM
#1
Ahha... So you want to control nocturnal emissions, huh? 
)
While I prefer neutral density filters for the finest lunar (visual) work, a pair of individual polarizing filters gives good results and is much friendlier to use, as the intensity may be varied through a wide range by rotating the eyepiece.
Depending on the type of scope and EP diameters you will be using, you'll need two or three individual polarizers (which are much easier to use than those already co-joined as one unit). My current scopes (Mak-Newt and refractors) and a penchant for 2" EPs required me to get three... two 48mm (for the 2" EPs) and one for the 1 1/4" EPs. I thread one of the 48's into the end of a short (2" x 1") extender for the Mak-Newt or into a diagonal for refractor use, and one into the field-lens end of the EP barrel (either 2" or 1 1/4" as needed).
Some nights I run the gamut from eyeball-frying low powers to much dimmer high powers, yet these allow me to find a comfortable viewing level by simply rotating the eyepiece to change the intensity. The only time I rotate both filters is when I'm trying to reduce daytime scatter and control intensity simultaneously. (The January 2000 issue of Sky & Telescope has an interesting article on pp 136-137, touting the use of polarizing filters for daytime viewing.) Otherwise, you don't need to dicker with the inner filter, as turning the outer one will do the trick.
... or for an even easier view of the moon:
http://www.astro-nut.com/gibbousmoon.jpg
Cheers,
Paul
--- http://www.astro-nut.com/ ---
)While I prefer neutral density filters for the finest lunar (visual) work, a pair of individual polarizing filters gives good results and is much friendlier to use, as the intensity may be varied through a wide range by rotating the eyepiece.
Depending on the type of scope and EP diameters you will be using, you'll need two or three individual polarizers (which are much easier to use than those already co-joined as one unit). My current scopes (Mak-Newt and refractors) and a penchant for 2" EPs required me to get three... two 48mm (for the 2" EPs) and one for the 1 1/4" EPs. I thread one of the 48's into the end of a short (2" x 1") extender for the Mak-Newt or into a diagonal for refractor use, and one into the field-lens end of the EP barrel (either 2" or 1 1/4" as needed).
Some nights I run the gamut from eyeball-frying low powers to much dimmer high powers, yet these allow me to find a comfortable viewing level by simply rotating the eyepiece to change the intensity. The only time I rotate both filters is when I'm trying to reduce daytime scatter and control intensity simultaneously. (The January 2000 issue of Sky & Telescope has an interesting article on pp 136-137, touting the use of polarizing filters for daytime viewing.) Otherwise, you don't need to dicker with the inner filter, as turning the outer one will do the trick.
... or for an even easier view of the moon:
http://www.astro-nut.com/gibbousmoon.jpg
Cheers,
Paul
--- http://www.astro-nut.com/ ---
Posted 07/27/2002 01:11PM
#2
A variable polarizing filter is useful for viewing a number of very bright objects such as the Moon, Venus, and Jupiter with larger scopes. Usually the transmission varies from about 3 to 40%. It is different than a polarizing filter sold for photographic use (the light transmission of the photographic version hardly varies at all).Either type will reduce reflections from most objects and increase color saturation.
A neutral density (or "moon filter") is cheaper but is more limited in its usefulness as the transmission is usually a constant 13% or so, limiting use to the moon.
Joplin
A neutral density (or "moon filter") is cheaper but is more limited in its usefulness as the transmission is usually a constant 13% or so, limiting use to the moon.
Joplin
Funding Member
