| This narrow 240 Ångstrom passband UHC (Ultra High Contrast) filter threads onto the 2” rear cell of 5” and larger Celestron Schmidt-Cassegrain telescopes and 7” and larger Meade Schmidt- and Maksutov-Cassegrains. It duplicates the 2” rear cell threads of those telescopes, allowing all visual accessories to be attached securely to the filter instead of the scope. It allows eyepieces to be changed quickly in a star diagonal without having to change the light pollution filter from one eyepiece to another. The filter is designed strictly for visually observing emission nebulas from badly light-polluted areas. The filter has excellent transmission at the visually important emission lines of hydrogen-beta at 4861Å and doubly ionized oxygen at 4959Å and 5007Å, which combines with the narrow passband to make emission nebulas stand out briskly against a dark sky. It can also be useful in hunting down and enhancing very faint nebulas from a dark sky observing site. It is not designed for astrophotography or for observing reflection nebulas. The filter has a passband 20% narrower than some competitive narrowband filters to give higher contrast on very faint objects. It has 2 to 4 times higher contrast than broadband filters, making it 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. The filter comes with individually-measured transmission data. Enter your telescope focal ratio in the formula box to the right to see what focal length eyepieces will work best with this filter. |
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