Lumicon Infrared Blocking Filter - 2"The Lumicon Infra-Red Blocking Filter completely blocks all Infra-Red light above ~750nm (7500 Angstroms). The versatile, anodized aluminum filter cell has 42mm male T-threads on one side and 48mm male threads with 42mm female T-threads, internal, on the other. Great for CCD camera I.R. blocking use. Lumicon Minus Violet and Infrared Blocking Filters are used primarily to "bracket" the color-corrected band of refracting telescopes. áThe Minus Violet and Infrared Blocking Filters can also be used as "visible" filters in RGBV (red-green-blue-visible) astrophotography with reflecting telescopes. The larger Minus Violet filters are for telephoto lenses. Most digital/CCD cameras have built-in infrared filters, in which case either the Minus Violet or Infrared filter may be used. The choice would depend on how far into the blue your primary lens is color-corrected. The Minus Violet filter blocks wavelengths shorter than about 420nm; the Infrared filter blocks wavelengths shorter than about 400nm. If your camera does not have a built-in infrared filter, the Infrared Blocking Filter is recommended, which blocks all wavelengths longer than 750nm.