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The Astronomik CLS blocks the light of the spectral lines of mercury and sodium-vapor lamps and lets the largest part of the visible light and H-alpha emissions pass. All the important emission lines, as well as the spectral region that the very well dark adapted eye can see, can pass through the filter.
The filters are optimized for use with aperture ratios from f/3 to f/15. Transmission losses and chromatic distortions, which are problems with other filters, only appear with Astronomik filters when extremely bright aperture ratios of f/2 and shorter are used. The CLS filter is suitable for use with telescopes of all aperture sizes.
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