Filter cutting the infrared spectrum longer than 690 nm. In the visible area, the transmission reaches 95%.
They allow taking photos of emission nebulas in the h-? range (this line - ? = 656 nm - is passed through the filter). Permeates UV without changes.
The filter has a 2 "filter thread on both sides of the luminaire, thanks to which it can be combined with other filters in this standard.The filter surfaces meet strict quality tolerances, while dielectric coatings guarantee scratch resistance and durability filter characteristics over time.
CCD and CMOS matrices are sensitive in the UV and IR areas (ultraviolet and infrared), while lenses of telescope lenses are not usually well corrected outside the visible spectrum, therefore the contrast of images without an IR filter can be lowered. The filter is recommended for astrophotography.
• fixing: through a 2 "filter thread
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!