Why do I need a specific Baader H-Beta filter for my CMOS camera?
Modern CMOS sensors have surfaces that are much more reflective than older CCD sensors. The Baader CMOS-optimized H-Beta filter has specialized anti-reflection coatings that prevent halos and internal reflections that can otherwise ruin an image when using bright stars for guiding or focusing.
What objects are best imaged with the Baader 5.5nm H-Beta filter?
The filter is specifically designed for emission nebulae that are strong in the Hydrogen-beta line. The classic targets that absolutely require an H-Beta filter to be seen clearly are:
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The Horsehead Nebula (Barnard 33) in Orion
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The California Nebula (NGC 1499) in Perseus
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The Cocoon Nebula (IC 5146) in Cygnus
Will the Baader 5.5nm H-Beta filter work for visual observing?
The filter is primarily designed for long-exposure imaging, and visual use is only practical, if at all, with very large aperture telescopes under dark skies. The 5.5nm bandpass is extremely restrictive, so it requires a lot of light-gathering power for the view to be bright enough for the human eye. For visual use, wider H-Beta filters are often preferred.
How does the 5.5nm bandpass affect my exposure times?
The 5.5nm bandpass is tighter than older 7nm or 8nm filters, meaning it rejects more background light. This may require you to increase your sub-exposure times slightly. However, the benefit is a much higher-contrast image, meaning you may need less total integration time to achieve a clean result.
Which size of the Baader 5.5nm H-Beta filter should I choose?
Choose the size that matches your camera sensor and filter wheel or holder. The 1.25" and 2" mounted versions suit standard filter holders and accessories. The 31mm and 36mm unmounted filters drop into dedicated filter wheels, such as those from ZWO and QHY, and offer a larger clear aperture than 1.25" mounted filters to help prevent vignetting on APS-C sensors. The 50.4mm round and 50x50mm or 65x65mm square filters are intended for large-format filter wheels and full-frame or larger sensors. Whichever size you choose, the Horsehead Nebula remains a demanding target: plan on long sub-exposures and several hours of total integration time.
Can I use the 5.5nm H-Beta filter with my color CMOS camera from a light-polluted location?
Yes, it is an excellent filter for that scenario. The 5.5nm bandpass is extremely effective at blocking out broadband light pollution from city skies. When used with a one-shot-color (OSC) camera, only part of the color pixels will record the signal, as H-beta is at the blue-green end of the spectrum. You will need to process the resulting image carefully to isolate the relevant channel data.
