A long pass filter is an optical filter designed to transmit light with wavelengths longer than a specific cutoff value while blocking or attenuating shorter wavelengths. These filters are often used in applications that require selective wavelength control, such as fluorescence microscopy, spectroscopy, photography, and machine vision.
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Optolong's Texas Red Filter is optimized for the Texas Red dye with specific Texas Red excitation and emission properties. It is ideal for Texas Red Spectrum imaging.

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My picture of crescent nebula NGC6888, placed in Cygnus constellation 4700 lights year away from earth. With L-extreme filter. Picture with stars removed to watch nebula details. Nebulosa creciente NGC6888 . Sin Estrellas para apreciar detalles. Madrid. #cielosESA #optolong