Astronomik IR-BLOCK filter in the frame 1.25 "/ 31.7 mm.
The IR blocking filter is commonly used with sensors with a low sensitivity in ultraviolet, typical for eg webcams, DSI and LPI cameras from Meade, and most video cameras. It allows you to eliminate most of the problems, such as image softness or halo around objects.
Thanks to very good UV and IR blocking, problems with the optical system for these spectral areas are avoided.
The filter optimized for light from f / 0.5 to f / 50. Typical transmission over 99%.
• protects the camera sensor, cuts out IR and practically all ultraviolet
• diffraction-limited accuracy
• parchocal with other Astronomic filters
• thickness: 1 mm
• resistant to moisture, scratch, does not age
IR/UV cut filter is considered a must be filter in most refractors. It will counteract so called "star bloating", which is due to increasing chromatic aberrations on the fringes of the visible spectrum. Especially important for ED/APOs, but also recommended for reflectors utilizing dedicated correction lenses, like coma correctors etc.
In any case this inexpensive filter is an easy way to cover a camera sensor or even better a DSLR mirror and sensor. It makes cleaning easier and maintenance less required. Also, a typical DSLR in a reflector... is simply open to the outside world.
Many forums and posts on the internet will tell you that "you should use an IR cut filter whenever you are not using other narrowband or multi-band filters".
As an example a great comparison screenshot from the equally great ZWO ASI FB group, taken with an apochromatic refractor.
(credit: Carl Björk @ZWO ASI FB group)
Happy star-hunting and clear skies!