The Baader C2 SWAN-Band-Filter with ≤ 15 nm Half-Band-Width isolates the two C2 lines at 511 and 514nm – leading to a contrast gain for comet hunters!
These two emission lines at 511nm and 514nm, named Swan bands after their discoverer, dominate the spectrum of a comet’s gas tail in the visible range. The filter allows only the light from the two carbon bands to pass through and, among other things, blocks the ubiquitous stray light, similar to a nebula filter in deep-sky observation. Structures in the gas tail thus become clearer even under good observing conditions. At the same time, the filter completely blocks the nearby OIII line at 501nm and below, which other Swan-Band filters allow to pass. The filter therefore allows for even higher contrast, and comets with gas tails can be distinguished even better from those dominated by a dust tail (and where a SWAN filter provides only a small contrast enhancement). For ambitious comet observers, a SWAN filter is part of the basic equipment.
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:
The Swan-Band filter is indeed a very special filter with central wavelength at 512 nm and ≤15nm half-width – for the first time without any O III transmission. It is therefore suitable for a variety of unusual applications some of which require further investigation, whether as an “O III parallel filter” to better remove stars from the image, or as a solar filter in a previously inaccessible section of the spectrum. We would be pleased about your experience reports also apart from the comet photography.
- The Baader SWAN-Filter has got all the advantages of the CMOS-optimized Baader filters:
- Increased contrast, matched for typical CMOS quantum efficiency and s/n ratio
- Reflex-Blocker™ coatings, for largest ever freedom from halos, even under most adverse conditions concerning aux-optics
- Identical filter thickness to existing standards, with utmost care for parfocality
- Blackened edges all around, with filter-lead-side-indicator in the form of a telescope-sided black outer rim, to additionally eliminate any reflection due to light falling onto the edge of a filter, making additional front-masks obselete
- Each filter coated individually, with sealed coating edge (NOT cut out of a larger plate with coatings left exposed, read more)
- Life-Coat™: evermore hard coatings to enable a non-aging coating for life – even in a most adverse environment