The Svbony UV/IR Block Filter (1.25") excludes unfocused infrared (IR) and ultraviolet (UV) light rays from imaging. Unlike the human eye - both CCD and CMOS system cameras are sensitive to these wavelength ranges, but lens systems cannot image them with visible light rays in the same focal plane. As a result, they create a disturbing halo (light fog) in the images as a lifeless spot.
This optical defect is not exclusive to the use of telescopes with lenses. In mirror systems, if a focus extender or a coma corrector using lenses is placed in the light path, a UV/IR block filter may also be required.
Cameras with a built-in UV/IR block filter are not required for these models.