Astro-Tech Ultra High Contrast (Uhc) Narrowband Filter For 1.25" Eyepieces

This Astro-Tech 1.25" Ultra High Contrast narrowband filter has a 320 Ångstrom FWHM passband (typically 220 Ångstroms at 90% transmission) for visually observing emission nebulas from heavily light-polluted areas. It is also useful for hunting down and enhancing very faint nebulas from a dark sky observing site. It is ideal for faint nebulas such as the Helix, Rosette, Veil, and North American. Brighter nebulas (such as the Omega, Dumbbell, Lagoon, etc.) stand out well under city lights. It is not designed for astrophotography or for observing reflection nebulas.

The filter has excellent transmission (typically 93-94%) at the visually important emission lines of hydrogen-beta at 4861Å and doubly ionized oxygen at 4959Å and 5007Å. This combines with the narrow passband and excellent rejection of off-band light to make emission nebulas stand out briskly against a dark sky. It has very steep passband cutoff slopes, to provide higher contrast than conventional narrowband filters that have more gradual transition slopes. 

Click on the Light Pollution Filter Formula under the Formula tab above and enter your telescope focal ratio in the formula box to see what focal length eyepieces will work best with this filter.

Max City Exit Pupil	4mm
Max Dark Site Exit Pupil	2mm
Min City Exit Pupil	1mm
Min Dark Site Exit Pupil	6mm
Weight	1 oz.
Warranty	1 year