Eliminate color fringing and darken the sky when looking through your achromatic telescope with the 2" Alpine Astronomical Baader Semi-APO Eyepiece Filter to make it perform more like an apochromat.
This specially-engineered filter combines the properties of the Baader Fringe Killer and Moon & Skyglow filters into a single unit with a strong violet-band cut to eliminate the need to stack filters, which can throttle light transmission and introduce other distortions. The high transmission and fringe reduction make it ideal for both planetary and deep-sky imaging. Additional coatings and precision polishing produce bright views with neutral color through-put.
UV/IR-cut coatings on the Semi-APO eliminate ultraviolet and infrared wavelengths to make it ideal for high-resolution imaging with webcams, DSLRs, and CCD cameras, whose sensors are sensitive to wavelengths outside the visible spectrum that can cause ghosting in images. Beyond general-purpose use, the Semi-APO is a great Mars filter when used on just about any telescope including large Dobsonians, Cassegrains, and Apochromats. The unique properties that result from the combination of the Fringe Killer's blue wavelength attenuation, plus the selective RGB (Red-Green-Blue) bandpasses, result in a contrast enhancement of Martian features.