Baader C2 Swan-Band Comet Filter (15nm)

Isolates Diatomic Carbon (C2) Swan Bands at 511nm & 514nm ≤ 15nm Passband Width Complete OIII Emission Line Blocking CMOS-Optimized with Reflex-Blocker™ Coatings Life-Coat™ Sealed Coating Edges for Durability Planeoptically Polished Substrate Available in 1.25" and 2" Mounted Formats Description FAQ Specifications In the Box Warranty Isolate the Ghostly Glow — The Baader C2 Swan-Band Comet Filter The Baader C2 Swan-Band Comet Filter is built around a single, demanding trade-off: achieving the highest possible contrast on cometary gas tails by isolating the faint C2 emission lines while aggressively rejecting all other signals, including the strong OIII line that contaminates competing designs. This is not a general-purpose nebula filter. It is a specialist tool engineered for the dedicated comet observer and imager who needs to pull the delicate, evolving structure of a gas tail out from the glow of the coma and the background sky. Unlike broadband or even standard nebula filters that offer a general contrast boost, the Swan-Band filter targets the specific physics of a comet. As a comet nears the sun, solar radiation causes its nucleus to outgas, creating a cloud of molecules. The most prominent emission in the visible spectrum from this gas tail comes from diatomic carbon (C2), which radiates strongly at 511nm and 514nm. This filter is your narrow window into that specific phenomenon, turning a faint smudge into a detailed structure. Targeted C2 Swan-Band Passband The core of the filter is its narrow passband, with a full-width at half-maximum (FWHM) of 15nm or less, centered at 512nm. This window is precisely tuned to capture the two bright C2 "Swan Bands" that give a gas tail its characteristic teal or blue-green glow. By accepting light almost exclusively from this molecular emission, the filter dramatically darkens the sky background, making faint tail streamers and condensations visible where they were previously lost in the noise. The Critical OIII Blocking Advantage The defining feature of Baader's design is its complete rejection of the Oxygen-III (OIII) emission line at 501nm. Many other filters designed for comets allow this line to pass, but OIII is not a significant component of a comet's gas tail. By including it, other filters brighten the background skyglow and the comet's dust coma, which reduces the specific contrast of the gas tail. Baader’s OIII-blocking approach ensures the only thing you see is the C2 emission, resulting in a darker field and higher-contrast tail structures. Engineered for Modern CMOS Sensors Modern CMOS sensors are notoriously reflective, often creating halos and internal reflections when paired with traditional filters. The Baader Swan-Band filter features fully optimized coatings that are angled to prevent light from bouncing between the filter and the sensor cover glass. This meticulous attention to reflection suppression means you can capture long exposures of a bright cometary nucleus next to a faint tail without the image being compromised by artifacts. Reflex-Blocker™ and Life-Coat™ Durability Baader’s proprietary Reflex-Blocker™ hard coatings provide superior transmission and anti-reflection properties, while their Life-Coat™ process seals the coating layers at the very edge of the glass. This is a critical, often overlooked feature that provides long-term durability. The sealed edges are impervious to moisture, preventing the slow degradation that can affect lesser filters after years of use in damp, real-world observing conditions. Preserving Optical Integrity with a Planeoptically Polished Substrate A filter is useless if it degrades the quality of your telescope's optics. Each Swan-Band filter is made from a fine-optically polished glass substrate, ensuring it is perfectly flat and parallel. This means it will not introduce astigmatism or other aberrations into the light path, preserving the pinpoint sharpness of stars and the finest details within the comet's structure. Your telescope's resolution is maintained, not compromised. Maximum Contrast from Blackened Edges To wring out every last bit of contrast, the edges of the filter glass are carefully blackened. This simple step prevents stray light from entering the side of the glass and reflecting internally into the eyepiece or camera sensor. It is one more small, but important, detail that contributes to a genuinely dark background and makes the faintest cometary features stand out. Observing Comet C/2023 A3 (Tsuchinshan-ATLAS) Imagine observing a bright comet as it makes its closest approach. Visually, without a filter, you see a bright, fuzzy coma and a hint of a tail. Now, thread in the Baader Swan-Band filter. The bright, dominant dust tail and coma dim significantly, and the sky background turns nearly black. As your eye adapts, the faint, blue-green gas tail begins to emerge, not as a uniform streak, but as a collection of fine, interwoven streamers and knots, revealing the dynamic interaction between the comet and the solar wind. Will the Swan-Band filter help me see any comet? This filter is most effective on comets that have a significant gas tail, which is rich in diatomic carbon. For comets that are dominated by a dust tail, which simply reflects sunlight, the filter will provide little to no contrast enhancement and will dim the view. Why does blocking OIII matter for a comet filter? Blocking OIII is critical because it's a major component of natural and artificial skyglow, but not a major emission from comets. By blocking it, the filter darkens the background sky and the comet's coma without dimming the C2 gas tail, dramatically increasing the tail's contrast. Can I use the Baader Swan-Band filter for nebula observing? No, this filter is not recommended for nebulae. It is designed to block the primary nebula emission lines like OIII and Hydrogen-beta. Using it on a nebula would result in a very dim, unsatisfactory view. It is a highly specialized tool for comets. Is this filter better for visual use or for imaging? It excels at both. For visual observers, it provides a dramatic increase in gas tail contrast. For imagers using monochrome or color CMOS cameras, it isolates the C2 signal for a dedicated luminance channel or enhances the green/blue channel data for a more detailed and colorful final image. What is the main trade-off of using this filter? The primary trade-off is its specialization. It significantly dims the comet's dust tail and nucleus to enhance the gas tail. You are choosing to sacrifice the view of the whole object to see extreme detail in one specific part of it. Filter Type Bandpass Comet Filter Central Wavelength 512nm Half-Bandwidth (FWHM) ≤ 15nm Primary Transmission C2 (Diatomic Carbon) at 511nm and 514nm Blocking Complete OIII line blocking at 501nm Substrate Planeoptically Polished Glass Coatings CMOS-Optimized, Reflex-Blocker™ Hard Coatings Durability Features Life-Coat™ Hermetically Sealed Edges Other Features Blackened Lens Edges Available Sizes 1.25" and 2" cell mounted Baader C2 Swan-Band Comet Filter × 1 Filter Storage Case × 1 Baader Planetarium Warranty