HOYA UV-IR filters.
These are specialized filters that cut BOTH UV rays below 390nm and IR rays above 700nm. This is important because the visible spectrum is between 400-700nm. Basically UV rays and IR rays both can diminish image clarity and sharpness. But by blocking them both before they get to the image sensor there is a noticeable increase in image quality.
Reviewed by 1 customers
Just starting in infrared photography and this is a great filter. Can't wait to continue with it.