| This 1.25” Oxygen III line filter has a very narrow 110 Ångstrom passband with excellent transmission of the nebula emission lines of doubly ionized oxygen at 4959Å and 5007Å. Its very narrow passband gives two to three times the contrast of a narrowband filter for observing brighter nebulas like M17 and M27 from heavily light-polluted city locations. It is excellent for visually observing very faint planetary and gaseous nebulas (such as M76 and Barnard’s Loop in Orion) that are normally invisible without a filter from mildly to moderately light-polluted sites. The narrow passband and high Oxygen III transmission combine to make emission and planetary nebulas stand out crisply against the blackness of space. It is not designed for astrophotography or for observing reflection nebulas. The filter comes with individually-measured transmission data. The filter is best with medium to large aperture scopes (6” and larger). 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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