Just in time for the introduction of this new C2 Swan-Band filter, a bright comet, comet C/2022 E3 (ZTF), offered itself as a test object and one of Baader Planetatrium’s customers (Mr Andreas Bringmann) was one of the first testers. The image of that comet is below and was taken from a city with an almost full moon. The image easily shows the amount of “doubly ionized carbon” (the carbon excited to glow radiates only in the wavelengths 511 nm and 514 nm ) emitted by the comet. The filter shows the complete extension of the ion cloud around a comet: Both thread sizes come with our proprietary pitch - which is not the same for the female and male threads. Today, filters are placed in the optical path of the telescope, even well in front of the focal plane. This definitely requires some degree of plane parallelism and accurate production of the filter glasses.

Based on these considerations, soon after the release of their new CMOS filter range, I asked Baader Planetarium if they would lend me a CMOS blue filter Baader RGB B-Filter – CMOS-optimizedThis is our own proprietary "emergency solution" for uniting a world were manufacturers all over the world copy from each other - to the point that there are almost a dozen different pitches in use for male and female threads. Traditionally US-companies used to do a UNF-based pitch and the rest of the world went for metric threads - but these do vary from 0.5 to 0.75.

I just bought LRGB 36mm unmounted filters. I have question: which side of filter should be placed towards telescope? Is it better way of distinguish than "more shiny surface towards telescope"? In the old days, colour filters for visual planetary observations were not screwed in the front part of the eyepiece, but were simply placed between the eyepiece and the eye. Plane-parallelism of these filter glasses was not important, because they were not in the optical path of the telescope. March 2021: The idea behind the visual use of blue filters from RGB palettes is that they have much higher transmittances in the blue value and steeper curve slopes than the usual blue filters known from planetary observation - e.g. the Wratten 80A/B/C filters or also Baader's dark blue 435nm and light blue 470nm filters. A CCD or CMOS blue filter allows much more light of the blue reflection nebulae of our galaxy to reach the eye and at the same time filters out the stray light in the green and yellow very effectively. The Baader C2 SWAN-Band-Filter with ≤ 15 nm Half-Band-Width isolates the two C2 lines at 511 and 514nm.It would be highly interesting to make a comparison exposing a comet through both an OIII filter and the new C2 filter. Thus, with the larger carbon gas cloud, one could deliberately highlight the inner nucleus of the comet. Also a only mag 16.2 faint C/2022 U2 (ATLAS), which is overtaken by the mag 5.8 bright C/2022 E3 (ZTF), could be photographed: In this blog our customer Ian Aiken gives some high level advice on what to look for when choosing a filter, coupled with reasoning why he choose the Baader's CMOS-Optimized LRGB and Ultra Narrowband f/2 filters, along with example LRGB and SHO images taken with these filters on his Celestron RASA 11 from his Bortle 7 suburban location.