The use of photometric filters in combination with normal RGB filters led to a significant increase in contrast in the dark nebulae regions. The application of SLOAN g', SLOAN r' and SLOAN i' enhanced the visibility of fine structures and details, while the RGB filters preserved the natural colors.
I used the three central filters used for the Sloan Digital Sky Survey (SDSS) divide the spectral range into three roughly equal parts: g': 410nm to 550nm, r': 555nm to 695nm, and i': 695nm to 845nm. These filters are therefore a good choice to consider for three-color imaging with modern cameras.
Normal Wavelength range of the Celestron RASA 11": The manufacturer specifies the Celestron RASA 11" with an optimized wavelength range of 400 to 700nm. However, the test with the SLOAN i' filter (695-845nm) clearly shows that a sharp and detailed image is also possible far beyond the fully corrected range. The prerequisite for this is the refocusing after each filter change.
Combination of RGB filters for "natural" colors: Using the RGB filters alone tended to reduce the contrast between my relatively strong light-polluted sky and the dark fog. The integration of photometric filters helped to increase this contrast, while RGB filters maintained the natural colors and enabled a balanced color in the final image. However, changing 9 different filters by hand was a task I don't want to repeat anytime soon ;)
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