Do I need the Baader f/2 Ultra-Highspeed filter for my f/5 telescope?
No, for systems at f/4 or slower, a standard Baader narrowband filter will perform excellently without significant band-shifting issues. The f/2 Ultra-Highspeed series is specifically engineered for the extremely steep light cones of systems like Celestron RASA, Starizona HyperStar, and other astrographs operating below f/4.
What happens if I use a standard H-alpha filter in my RASA at f/2?
If you use a standard, non-shifted narrowband filter in an f/2 system, you will experience significant signal loss. The filter's passband will shift away from the H-alpha emission line, effectively blocking a large portion of the light from the nebula you are trying to capture. This results in faint, low-contrast images, regardless of exposure time.
How does the 3.5nm bandpass on this Baader filter affect my images of the Orion Nebula (M42)?
The 3.5nm bandpass will produce extremely high contrast on the hydrogen gas structures within the Orion Nebula (M42). It will darken the sky background significantly, making the faint outer loops of the nebula more visible while retaining sharp detail in the bright Trapezium region. The CMOS-optimization will also help control the intense brightness of the core stars, reducing halos.
Which size of the Baader 3.5nm f/2 Ultra-Highspeed H-alpha filter do I need?
Match the size to your filter wheel or drawer and your sensor. The 1.25" and 2" versions come in standard mounted cells, the 2" cell carrying M48x0.75 threads. The unmounted 31mm size suits many ZWO and QHY wheels for APS-C or smaller sensors, while 36mm fits larger wheels and drawers for sensors the 1.25" format cannot cover without vignetting. The 47.4mm unmounted filter is made for FCCT filter holders on Celestron RASA astrographs, and the 50.4mm round and 50x50mm or 65x65mm square formats cover full-frame and larger sensors. Unmounted filters have no threads and need a compatible holder, drawer or wheel. All sizes are intended for astrophotography only, not visual use.
What does 'CMOS-optimized' mean for the Baader 3.5nm H-alpha filter?
'CMOS-optimized' means the filter features advanced anti-reflection coatings designed to prevent halos that can occur from light reflecting between the filter and a modern, highly-reflective CMOS sensor. This results in cleaner stellar profiles and higher-quality raw data.
Will the 3.5nm bandpass require longer exposure times than a 7nm filter?
Yes, all else being equal, a narrower bandpass gathers less light per unit of time. However, this filter is designed for ultra-fast f/2 systems, which gather light at an exceptional rate. The combination of the fast optics and the high-contrast filter allows for shorter total integration times to achieve a high signal-to-noise ratio, even with longer individual sub-exposures.
