| This narrow passband Bandmate 1.25" Oxygen III line filter has excellent transmission of the nebula emission lines of doubly ionized oxygen at 4959Å and 5007Å, with high blocking of unwanted longer wavelengths. 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 works best with medium to large aperture scopes (6" and larger). The filter substrate is ground and polished optical quality BK7 glass. This yields sharp star images, even when the filter is placed in front of the star diagonal. Such a location results in a long light path between the filter and eyepiece. This can reduce the image sharpness in lesser filters whose glass substrates are not polished to the same plane and parallel accuracy as TeleVue filters. Ion beam coating technology and the high quality optical glass produces low scatter in its stable hard coating. This reduces passband changes due to temperature and humidity. Each filter is checked optically and cosmetically to assure performance and each is individually serialized. The TeleVue Oxygen III filter works well for observing nebulas like M97 (Owl Nebula), M27 (Dumbbell Nebula), M57 (Ring Nebula), M42-43 (Orion Nebula), M1 (Crab Nebula), NGC 6992-6995 (Veil Nebula), NGC 6826 (Blinking Nebula), and NGC 6543 (Cat’s eye Nebula). While none of these objects requires a nebula filter to find or enjoy from a dark sky observing location, they are all objects that nebula filters are designed to enhance. The filter 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. Some nebular objects, like the Dumbbell (M27), can be difficult to observe from heavily light-polluted city locations. If you must observe from a city location, this filter may realistically be your only hope for spotting some of these objects. Special filtering in the TeleVue passband design reduces the red tinge in stars so often seen in lesser filters. It also allows for sharp and bright views of star clusters embedded in nebulas, such as M8 (the Lagoon). This TeleVue filter does not dim these stars to the extent traditional filters do. The TeleVue nebula/star brightness balance is more realistic. In addition to better views of embedded star clusters, the TeleVue Bandmate Oxygen III filter shows more stars in the background field than traditional filters. Here are a few comments about this effect from on-line customer comments. “The nebulae were being equally enhanced with the Bandmates but not at the expense of filtering out the background star field to the degree seen in competitive filters. In addition, the star colors appeared, in the Bandmates, truer. How is this done? Not a clue, but the difference is more than just subtle. The resulting views through the Bandmates were to me more realistic and aesthetically more pleasing. I noticed this most on M42 and the Dumbbell where the field stars add greatly to the enjoyment of the over all view. To date the two Bandmate Nebula filters are the best that I have ever used."
“I was very surprised at how many stars were visible with the filter in place. Also, the stars are esthetically pleasing and were not artificially tinged red which I’ve heard happens with other filters. The filter was placed before the diagonal making it a breeze when changing eyepieces." 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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