OWL Astronomy

OWL Astronomy Products
Eyepieces, Telescopes, Binoculars, Microscopes
Optical Color Filters

Optical Color Filters

Bring out all the detail in the planets.

Back in the days of black and white photography, it was know that details on your photos could be emphasized by the proper choice of color filters. In general color filters make objects of about their own color lighter and objects of the opposite color darker. For this reason, an orange filter makes the main body of Mars lighter and makes the greenish-brown markings darker. This tends to increase the contrast of details in the planet. On the other hand, a blue or green filter will tend to make the main body of Mars dark which brings out the polar caps. Many observers spend a lot of money on expensive telescopes and eyepieces and then complain they cannot see a lot of detail on the planets. Inexpensive color filters will show you more detail using good quality but not expensive eyepieces. This is probably the most overlooked observing aid.

Although there are a large variety of color filters listed here, normally all of these are in stock. These filters are used by a number of suppliers of astronomical accessories at much more than our great prices.

The major colors of filters (red, green, blue, yellow) are available in three depths of color (light, medium, and deep). In general the different depths bring out the same features. You would choose the lighter ones for smaller aperture telescopes and viewing through hazy skies on the larger ones. The deeper colors are for larger aperture scopes on clear days. For any planet details you will have to experiment. Different filters will bring out different details and some nights the best filter changes.

All of our filters are threaded to fit the standard size eyepieces: 1.25 inch (31.8 mm) and 2 inch (50.8 mm). Because the thread inside the eyepieces, the actual filter sizes are slightly less than the eyepieces. A 2 inch filter (actually a filter for a 2 inch eyepiece) is 48 mm. While threading the filters onto the eyepiece is best for photography, for visual observations we like to move the filters back and forth across the view. This tends to make various details snap in and out of view. These changes make these details more noticeable. Try this method to see if it works for you. The following table lists some of the main uses of filters of for several objects. These are our opinion, and these may not always agree with what other observers may recommend.

Object Main Filters Special Feature Filters
Venus Use red and deep red filters for observing Venus during the day and twilight hours. Blues and deep blues may bring out some cloud features. For observing Venus against a dark sky, a neutral density filter may be useful.
Jupiter Various shades of yellow, orange, and red are used for the main features on Jupiter. Our favorite is #21, orange. Blues and greens bring out the red/brown features including the Red Spots. The #11 filter (yellow-green) works well on bluish features such as festoons between the bands. Because features may be almost any color, try a number of colors to see if additional features are made visible.
Saturn Various shades of yellow and orange are used for the main features on Saturn. Our favorite is #21, orange. Because it is not as bright a planet as Jupiter, most of the time reds would be too dark unless you have a large scope. Because features may be almost any color, try a number of colors to see if additional features are made visible. The use of blues and violet may bring out some details in Saturn's ring system. Saturn is like a Jupiter with much more subtle contrast details.
Moon The main filters for the Moon would be ones to remove some of the brightness especially for the phases near the full moon. Use neutral density filters if you are taking color photos. Deep green and greenish-gray filters are the most popular moon filters. There is almost no color visible on the moon. Some subtle colored features may me brought out using shades of yellow for some and blue for others.
Double Stars There are some double stars where a bright primary star of one color drowns out a faint companion of a different color. A good example of these is with Anatres. Antares is a 1.0 magnitude red star with a 5.4 magnitude greenish companion. A light green or yellow-green filter will dim the primary relative to the secondary. Neutral density filters may be used to dim a bright primary.
Deep Sky Most of the time special deep sky filters will work better than standard color filters. Try a light green or light blue filter on emission and planetary nebula. These should aid in removing some light pollution in regions of the spectrum away from the nebula emission lines.

1.25 Inch Color Filters

Filter Photo Color Transmission Purchase ($7.00 each)
#23A Light Red 25%T
#25 Medium Red 14%T
#21 Orange 46%T
#8 Light Yellow 83%T
#12 Medium Yellow 74%T
#11 Yellow-Green 78%T

#56 Medium Green 24%T
#58A Deep Green 18%T

#82A Light Blue 83%T
#80A Medium Blue `` 30%T
#38A Deep Blue 17%T

#47 Violet 5%T

#ND13 Deep Neutral Density (Moon Filter) 13%T

You may choose your own sets of Color Filters.
(Sets must be all different colors)
Give us a call if you would like us to recommend a set for you.
Four Color Filters
Sale Price: $24.95.
Enter Any Four (4) Color Filters:
Six Color Filters
Sale Price: $36.50.
Enter Any Six (6) Color Filters:
Eight Color Filters
Sale Price: $47.95.
Enter Any Eight (8) Color Filters:

Variable Density Eyepiece Moon Filter Set
Brand New in Cases

Specially Chosen for Lunar Observations
Made Exclusively for Knight OWL

Fit all Standard 1.25" (31.75 mm) Diameter Eyepieces

This set consists of two polarizing filters. When used together, these
provide a wide-range, variable neutral density filter. These are especially
good for lunar observations over the full range of the lunar cycle.
These also may be used for photography of polarized astronomical objects.

Set of Variable
                                      Density Moon Filters
Set of variable density filter in two cases.

Set of Polarizing Filters
View of two filter screwed together for use.

Set of
                                      Polarizing Filters - Low Desity
Filters adjusted for low density.

Set of Polarizing Filters -
                                      Medium Desity
Filters adjusted for medium density.

Set of
                                      Polarizing Filters - Highest

Filters adjusted for  highest density.

When observing the Moon, especially near the full Moon and at low powers, the Moon can be so bright in the telescope that your eyes are dazzled and few details are visible. This filter set is used to decrease the light levels and provide comfortable viewing.  With a standard moon filter, the density might be too great during much of the lunar cycle. This set of variable density filters shown here are adjustable over a wide range to provide a full range of densities. While we did not measure the range, this filter set will provide a range from about 2% transmission at the highest density to about 60% transmission at the lowest density.

While many moon filters are a slightly greenish-gray, this filter is only gray at all densities and adds no color to the image. It is ideal for taking color photos of the moon and other objects when you do not want a color shift. These filters are packaged in two plastic cases for protection.

In addition to the normal intended use of these filter sets for lunar observations, these filters have another very interesting feature. When you take a photo of an astronomical object that emits polarized light, these polarizing filters will allow the polarized light from the object to be recorded and measured. The brightest object of this type is the Crab Nebula - M1. A polarizing filter also may be used to reduce haze and glare in daylight photography

This filter will not change the color of the image so it is ideal for color photography of bright objects.

Price: $19.95
(Limited time only!)

2 Inch Color Filters

The number given with the filter color is about the corresponding Wratten number
Each 2 inch color filter is $16.95. Save more by buying a set.

Light Red (#23A)

Orange (#21)

Medium Yellow (#12)

Medium Green (#56)

Medium Blue (#80A)

Neutral Density - Moon Filter (13%)

2 Inch Filter Set - All 6 Filters Above

Only $79.95 for the set

Last Updated June 23, 2012