The ultraviolet and infrared regions are beyond the normal range of the human eye when stars are observed visually with the unaided eye or through binoculars or a telescope. However, the extended sensitivity imaging chips of many CCD cameras, webcams, and DSI-type cameras can be overloaded by the stars’ UV and IR output and bloat unnaturally in CCD images. This 1.25” Astro-Tech imaging filter has a 240nm FWHM (Full-Width at Half-Maximum transmission) passband with an extremely sharp cutoff of all UV radiation below 430 nanometers and an equally sharp cutoff of all IR radiation above 670 nanometers. It passes between 92% and 98% of the visible and photographically-important light between these extremes, so CCD images record the stars essentially as they would appear to the human eye. This makes this Astro-Tech filter an excellent choice as a luminance filter in LRGB imaging. Its sharp IR cutoff likewise makes it very useful with monochrome cameras that do not have a built-in IR filter.

The Astro-Tech filter also works to sharpen surface details in planetary CCD images. It is particularly effective at improving the contrast of Martian features. While the eye can’t see the IR radiation of sun-illuminated planetary surfaces, the sensitive imaging chips of many CCDs and webcams can be overloaded by the planet’s IR glow, blurring surface and cloud detail. This filter sharpens planetary detail by blocking the invisible IR portion of the spectrum before it can overload the imaging chip.

The filter uses high quality multi-layer ion-deposited hard dichroic interference coatings on an optical glass substrate. The filter is mounted in a standard 1.25" threaded cell and will fit any CCD camera or filter wheel that accepts 1.25" filters. The filter comes in a hard plastic protective case.