Astro-Tech #38A Dark Blue 1.25" Color Filter

If you have a big scope (10" in aperture and larger), this #38A dark blue Astro-Tech 1.25" eyepiece filter can be useful when observing Jupiter's belts and features on Mars during periods of violet clearing 

Recommended applications for this filter:

Moon - Somewhat useful for improving contrast between lunar features in scopes 8" and larger.

Mercury - May improve observations of rarely visible dusky surface features at twilight, when the planet is near the horizon.

Venus - Increases contrast of occasional faint dark shadings in upper Venusian clouds.

Mars - Useful for enhancing the visibility of surface features and localized dust storms, clouds, and ice fogs with 8" or larger scopes, particularly during the still-unexplained phenomenon of violet clearing (when the Martian atmosphere - normally a bright, featureless disc in violet light due to the scattering of short wavelengths of light by the thin atmosphere - becomes transparent through a violet or blue filter, revealing large dark surface features).

Jupiter - Primarily used for enhancing the boundaries between the reddish belts and adjacent bright zones in the upper atmosphere. Helpful in defining the Great Red Spot and festoons in the belts.

Saturn - Enhances low-contrast features between the belts and zones in the planetary disc.

Comets - Brings out the best definition in comet gas tails. Useful with 10" and larger scopes for observing orange Sodium D lines in gas tails when combined with #21 filter.

17% transmission