| This broadband filter is designed to thread onto the 2" rear cell threads of 8" and larger Meade and Celestron Schmidt-Cassegrain telescopes, in front of the visual back and star diagonal. It will also fit the rear cell of the 7" Meade Maksutov-Cassegrain (but not the 5" aperture and smaller Meade Maksutovs). The rear cell design makes it easy to use the same filter for a number of different eyepieces, but is less convenient to use if you have several different filters to use with those eyepieces. The filter is supplied in a protective hinged plastic box. This broadband filter has high transmission in the photographically important (but visually unseen) crimson portion of the spectrum. This makes it very usable for long exposure astrophotography, as well as visual observing. Its use with off-axis guiders is somewhat problematical, however, as it filters the light going to the guiding eyepiece as well as the camera. This dims the brightness of guide stars by up to 90% and makes them difficult to see. Visual filter bandwidth at the 50% transmission point is quite wide – typically a little under 700Å (70nm) – from about 4600Å to 5300Å. Peak visual transmission is from 4650Å to 5200Å and varies irregularly between 92% and 94%. Transmission of the photographically important ionized nitrogen and hydrogen-alpha lines near 6570Å in the crimson portion of the spectrum varies between 75% and 85%. These transmission figures are not guaranteed, but can vary slightly up or down due to production tolerances in applying the tens of individually ion-deposited layers that make up the sophisticated filter coating. 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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