Astronomik XT filters for wide-angle optics: With these filters, you can obtain beautiful star images right into the corners of the image, even with extreme wide-angle shots.
With other Astronomik filters, the image quality in the corners of the image is limited at short focal lengths (wide angle): Although the filters consist only of a one-millimetre-thick glass plate that carries the filter layers, this plate causes aberrations with certain types of short-focal-length lenses, and the stars are pulled apart into lines.
Astronomik's XT filters are mounted on an extremely thin carrier substrate that is only 0.3 millimetres thick. This reduces "star streaks" in the corners of the image to a minimum.
The extremely thin carrier substrate of the XT filters is, of course, finely polished, stress-free and meets the highest demands of astrophotographers worldwide in every respect.
Despite this ultra-thin glass, Astronomik XT filters feature the same coating technology found in all Astronomik filters: completely scratch-resistant, moisture-resistant and non-ageing. The filter will retain 100% of its performance even after many years.
The luminance channel is very important for successful astrophotography! The sharpness, contrast and low noise of the luminance data are crucial for achieving the best possible quality in the final result!
The task of the L filter is to have maximum transmission across the entire visible spectrum, because the combination of the widest possible passband and high transmission allows the greatest possible number of photons to be captured.
Not all telescopes or additional elements such as correctors, field flatteners and Shapley lenses have perfect colour correction. An L filter with too wide a bandwidth allows wavelengths to pass through for which your optics are not properly corrected. The result is unattractive bloated, blurred stars that do not match the RGB colour channels.
Astronomik presents three different UV+IR block filters for the luminance channel, designated L-1, L-2 and L-3. Please pay attention to the corresponding designation in the product name.
How to find the right luminance filter: Depending on the colour correction of the instruments used, the L filter with the largest transmission 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 optics can be classified as colour-accurate, the L-1 filter is the right choice. For general use, e.g. on telescopes with different colour purity or when using additional light-refracting elements in the beam path, we recommend the Astronomik L-2 version. For "colourful" optics, e.g. an achromatic lens, we recommend the Astronomik L-3 filter to increase the sharpness of the image.
The transmission properties and coating technology of the new Astronomik L series have been developed so that no halos or reflections are visible. Even with bright stars in the field of view, nebulae and galaxies are reproduced 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 durable coating applied to a special fine-optical substrate, as used in space flight. The basic requirements for such material are freedom from streaks, tension and bubbles. Furthermore, the Astronomik filter carriers are processed to the same thickness in a separate work step: Perfect homofocality and minimal keystone distortion are the resulting advantages!
Tip: Use the Astronomik CLS filter instead of a luminance filter! You will receive an L signal without the lines from sodium and mercury lamps and with much less background noise.
