The luminance channel is very important for a successful astrophoto! Sharpness, contrast and low noise of the luminance data are crucial to be able to achieve the best possible quality in the finished result!
The task of the L-filter is to have the maximum transmission over the entire visible spectrum, because the combination of the widest possible transmission and high transmission makes it possible to detect the largest possible number of photons.
Not all telescopes or additional elements such as correctors, field flattener and Shapley lenses have a perfect color correction. A broadband L-filter can pass wavelengths for which your optics are not properly corrected. The result is unattractive bloated, fuzzy stars that do not match the RGB color channels.
Astronomik presents three different UV + IR block filters for the luminance channel, they will be labeled L-1, L-2 and L-3. Please pay attention to the corresponding name in the product name.
How to find the right luminance filter: Depending on the color correction of the instruments used, the L filter with the largest aperture should be used. The L-1 filter has by far the largest spectral transmission, whereas the L-3 filter has the narrowest spectral window. If your used optics can be classified as color defect free, the L-1 filter is the right choice. For general use, eg. For example, on telescopes of different color purity or the use of additional, refractive elements in the beam path, we recommend the Astronomik L-2 version. For a "colorful" look, such as an achromatic lens, we recommend the Astronomik L-3 filter to increase the image sharpness.
The transmission characteristics and coating technology of the new Astronomik L series have been designed to eliminate the effects of halos or reflections. Even with bright stars in the field of vision, nebulae and galaxies with the finest structures and the highest contrast are depicted.
Like all Astronomik filters, the L-1, L-2 and L-3 filters have an extremely durable and durable coating applied to a fine optical specialty substrate as used in aerospace applications. The basic requirement for such material is freedom from streaks, tension and bubbles. Furthermore, the Astronomik filter carriers are machined to the same thickness in a single operation: perfect homofocality and minimal wedge error are the resulting benefits!
Tip: Use the Astronomik CLS-CCD filter instead of a luminance! You get an L signal without the lines of sodium and mercury lamps with much less background noise.