The luminance channel is very important for a successful astrophotography! The sharpness, contrast and low-noise of the luminance data are decisive in achieving the best possible quality in the final result!
The task of the L filter is to have the maximum transmission over the entire visible spectrum, since the combination of the widest possible transmission and high transmission makes it possible to detect the greatest possible photon number.
Not all telescopes or additional elements such as correctors, field planers and Shapley lenses have a perfect color correction. A too wide-band L filter lets you pass wavelengths for which your optics have not been properly corrected. The result is unpleasantly inflated, blurred stars, which do not match the RGB color channels.
Astronomy presents three different UV + IR block filters for the luminance channel, they are designated 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, while the L-3 filter has the narrowest spectral window. If your optics can be classified as color-defect-free, the L-1 filter is the right choice. For general use, Eg 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, for example an achromat, we recommend the Astronomik L-3 filter to increase the image sharpness.
The transmission characteristics and the coating technology of the new Astronomik L series have been developed in such a way that no halos or reflections are visible. Even with bright stars in the face field, fog and galaxies are depicted with the finest structures and the highest contrast.
Like all filters from Astronomik, the L-1, L-2 and L-3 filters have an extremely resistant and long-lasting coating, applied to a fine-optical special substrate as it is also used in space travel. The basic prerequisite for such material is streak, tension and bubble freeness. In addition, the astronomy filter carriers are processed to the same thickness in a separate work: perfect homo-co-openness and the least amount of reeds are the resulting advantages!
Tip: Use a CLS-CCD filter instead of a luminance astronomy! You get an L signal, without the lines of sodium and mercury lamps with much less background noise.