What are the different types of eyepiece filters: Colored, Neutral Density and Polarizing?

Eyepiece filters are an invaluable aid in lunar and planetary observing. They reduce glare and light scattering, increase contrast through selective filtration, increase definition and resolution, reduce irradiation and lessen eye fatigue.

Most quality eyepieces have threads in the base of the tube to accept filters. Many manufacturers use the same threading.

The effectiveness of the filters depends on several factors, including: the aperture and focal length of the telescope, the magnification being used, and seeing conditions. Here are descriptions of what to expect from each filter: Yellow, Orange, Red, Blue, Green, Violet, ND and Polarizing–in different observing situations. At the same time, you’ll become familiar with the astounding variety of enhancements available through these simple accessories. Also given for each filter is the percentage of light transmitted (T).

Yellow

#12 Deep Yellow 74% T
#15 Deep Yellow 67% T

  • Moon – Enhance lunar features.
  • Jupiter – Penetrate and darken atmospheric currents containing low-hue blue tones. Enhance orange and red features of the belts and zones. Useful for studies of the polar regions.
  • Mars – Reduce light from the blue and green areas which darken the maria, oases and canal markings, while lightening the orange-hued desert regions. Also sharpen the boundaries of yellow dust clouds.
  • Neptune – Improve detail in larger telescopes (11" and larger apertures).
  • Saturn – Penetrate and darken atmospheric currents containing low-hue blue tones. Enhance orange and red features of the belts and zones.
  • Uranus – Improve detail in larger telescopes (11" and larger apertures).
  • Venus – Reveal low-contrast surface features.
  • Comets – Enhance definition in comet tails.

#8 Yellow 83% T

All observing information for this filter is the same as that given for the #12 and #15 Deep Yellow filters, with the exception of the following:

  • Mars – Improves the Martian maria by reducing scattered light from blue areas, while allowing passage of additional green light for studying yellow dust clouds.
  • Comets – Brings out highlights in yellowish dust tails and enhances appearance of comet heads.

Orange

#21 Orange 46% T

  • Moon – Greatly enhances lunar features.
  • Jupiter – Improves appearance and detail revealed in structure of Jovian belts. Enhances viewing of festoons and polar regions.
  • Mars – Reduces light from the blue and green areas which darken the maria, oases and canal markings, while lightening the orange-hued desert regions. Also sharpens the boundaries of yellow dust clouds.
  • Mercury – Reduces the brightness of blue sky during daylight observing, to reveal surface features.
    Saturn – Improves structure of the cloud bands and highlights blue polar regions.
    Venus – Use during daylight observing to reduce brightness of blue sky.
    Comets–Enhances definition of comet dust tails and heads in larger telescopes (11" and greater aperture).
    Solar – When using some Mylar Solar Filters, adding this orange filter will give a truer color rendition.

Red

#25 Red 14% T

  • Moon – Improves lunar features.
  • Jupiter – Useful for studying bluer clouds.
  • Mars – Ideal for observation of the polar ice caps and features on the Martian surface. Sharpens the boundaries of yellow dust clouds.
  • Mercury – Improves observation at twilight, when the planet is near the horizon. During daylight, it reduces the brightness of the blue sky to enhance surface features.
  • Saturn – Useful for studying bluer clouds.
  • Venus – Use during daylight observing to reduce brightness of blue sky. Occasionally deformations of the terminator are visible.

#23A Light Red 25% T

All observing information for this filter is the same as that given for the #25 filter, with the exception of the following:

  • Mars – Reduces light from blue and green areas which darkens the maria, oases and canal markings, while lightening the orange-hued desert regions. Sharpens the boundaries of yellow dust clouds.
  • Comets – Improves definition of comet dust tails. 

Blue

Light Blue 30% T
#82A Pale Blue 73% T
#38A Blue 17% T

  • Moon – Enhance lunar detail.
  • Jupiter – Enhance the boundaries between the reddish belts and adjacent bright zones. Useful for viewing the Great Red Spot.
  • Mars – Very useful during the violet clearing. Helpful in studying surface features and polar caps.
  • Mercury – Improve observation of dusky surface markings at twilight, when the planet is near the horizon.
  • Saturn – Enhance low-contrast features between the belts and zones
  • Venus – Useful for increased contrast of dark shadings in upper Venusian clouds.
  • Comets – Bring out the best definition in comet gas tails.

Green

#56 Light Green 53% T

  • Moon– Enhances lunar features.
  • Jupiter – Increases visibility of the Great Red Spot. Useful for observing the low-contrast hues of blue and red that exist in the Jovian atmosphere.
  • Mars – Excellent for increased contrast of Martian polar caps, low clouds and yellowish dust storms.
  • Venus – Useful for Venusian cloud pattern studies. Reduces brightness of blue sky during daylight observing.

#58 Green 24% T

All observing information for this filter is the same as that given for the #56 Green filter, with the exception of the following:

  • Saturn – Enhances white features in the Saturnian atmosphere.
  • Comets – Useful for observing brighter comets.

Violet

#47 Violet 3% T

  • Mars – Useful for detecting high clouds and haze over the Martian polar caps.
  • Mercury – Helpful in detecting faint features.
  • Saturn – Good for ring structure studies.
  • Venus – Increases contrast of dark shading in upper Venusian clouds.
  • Comets – Useful for observing brighter comets. 

#96ND (Neutral Density)
#96ND 50% T – Density 0.3
#96ND 25% T – Density 0.6
#96ND 13% T – Density 0.9

  • Moon – Excellent for reducing irradiation, glare and subject brightness. Colors are unaltered, as light is transmitted uniformly over the entire spectrum. Each model performs somewhat differently, depending on the brightness of the Moon.
  • Planets – Stacking in combination with color filters lowers transmission, but retains true color balance for specific applications. Reduces glare on brighter planets and minimizes irradiation.
  • Binary (Double) Stars – Helpful in splitting binary stars, because it reduces glare and diffraction effects around the brighter star of the binary pair.

Polarizing

Reduces reflected polarized light in the Earth’s atmosphere.

  • Moon & Planets – Invaluable in reducing irradiation and glare.
  • Binary Stars – Helpful in splitting binary stars, because it reduces glare and diffraction effects around the brighter star of the binary pair.


Updated 12/21/13