Celestron Hα-Hβ-OIII Imaging Filter for RASA 8 – Narrowband Filter Designed for f/2 Astrophotography (#93619)
Maximize contrast. Minimize skyglow. Unlock nebular detail from even the most light-polluted skies.
The Celestron Hα-Hβ-OIII Imaging Filter was purpose-built for the unique demands of the 8” Rowe-Ackermann Schmidt Astrograph (RASA). This narrowband filter transmits only the essential emission lines from hydrogen-alpha, hydrogen-beta, and oxygen-III—wavelengths that define the glowing clouds of emission nebulae—while blocking skyglow and light pollution across the rest of the visible spectrum. The result? Nebulae that pop against a jet-black background, even under suburban skies.
Engineered for Fast Optics
Standard narrowband filters, while great for slower systems, often fall short when used with fast f/2 optics like those in the RASA 8. The steep light cone shifts the incoming wavelengths, effectively moving them out of the narrow bandpass range. This causes other filters to inadvertently block the very light you’re trying to capture—reducing brightness and degrading detail.
Celestron’s Hα-Hβ-OIII Imaging Filter is different. It’s custom designed for the RASA 8's f/2 speed, with optimized bandpasses that compensate for spectral shift. That means you keep the light you want—at full strength—without compromise.
Superior Contrast for Emission Nebulae
This filter is ideal for imaging classic emission nebulae, such as:
By passing only the Hα (656nm), Hβ (486nm), and OIII (496nm/501nm) wavelengths—and rejecting more than 99.5% of other light—this filter dramatically improves image contrast and removes background washout. Whether you’re imaging from a light-polluted backyard or a dark site, you’ll see finer filamentary structures, sharper contrast, and more defined color separation in your images.
Note: As a true narrowband filter, it is not ideal for broadband objects like galaxies or open star clusters.
Thoughtful Construction and Optical Integrity
The filter is housed in a black anodized aluminum cell with a knurled edge for easy installation—even with gloved hands. It fits directly into the integrated filter mount in the RASA 8 front lens cell, replacing the clear optical window that normally ships with the scope. No adapter needed. And because the filter maintains the correct optical thickness, image performance and spacing remain unaffected.
Each filter is made with precision-ground Schott B270 glass, with dichroic multi-bandpass and multi-layer anti-reflection coatings to maximize throughput and suppress reflections. The surfaces are optically flat and defect-free, ensuring you don’t introduce distortion or ghosting into your imaging train.
Filter Includes:
-
Celestron Hα-Hβ-OIII Filter in anodized aluminum cell
-
Protective foam-lined plastic storage case
-
Threaded retaining ring
-
Factory-measured spectral transmission graph unique to your filter
Technical Specifications
-
Glass Type: Schott B270
-
Glass Thickness: 2mm (0.078")
-
Filter Diameter: 46mm (1.81")
-
Clear Aperture: 43mm (1.69")
-
Coatings: Dichroic narrowband pass + multi-layer anti-reflection
-
Filter Housing: CNC-machined aluminum, black anodized, knurled grip
-
Transmission: ≥85% at 486nm, 496nm, 501nm, 656nm; <0.5% elsewhere
-
Compatibility: Designed exclusively for Celestron 8” RASA
-
Not compatible with: RASA 11 or 36, standard SCTs, or systems slower than f/2.2
Final Thoughts
If you're serious about capturing emission nebulae with your 8" RASA, this is the filter you've been waiting for. Unlike generic narrowband filters that struggle with fast optics, the Celestron Hα-Hβ-OIII filter gives you the full signal from your target while erasing the light pollution around it. It’s a precision tool designed for one purpose: making deep-sky objects stand out in all their glory—even under imperfect skies.
