Optical filters, generally, belong to one of two categories. The simplest, physically, is the absorptive filter, while the latter category, that of interference or dichroic filters, can be quite complex.
(Optical Filters) Additives which selectively absorb, reflect, or transmit a certain area of the solar energy spectrum, thus enabling manipulation of that radiation in a desired way.
(Optical Filters) These filters selectively allow for different frequency light to pass through.
the infrared region of the electromagnetic spectrum; electromagnetic wave frequencies below the visible range; "they could sense radiation in the infrared"
(of equipment or techniques) Using or concerned with this radiation
having or employing wavelengths longer than light but shorter than radio waves; lying outside the visible spectrum at its red end; "infrared radiation"; "infrared photography"
'Infrared (IR)' light is electromagnetic radiation with a wavelength between 0.7 and 300 micrometres, which equates to a frequency range between approximately 1 and 430 THz.
(of electromagnetic radiation) Having a wavelength just greater than that of the red end of the visible light spectrum but less than that of microwaves. Infrared radiation has a wavelength from about 800 nm to 1 mm, and is emitted particularly by heated objects
Infrared - Winter Wind in Cocos Palm
Following the demise of my trusty but troubled S5600, I manage to get a Finepix S5800 at an excellent ebay price. Once modded with a piece of optical glass in place of the hot-mirror, I took this pic as the first test shot. FUJI S5800, f=5.0, exp 1/60, iso=100 and a 680nm filter...and of course a little channel swapping with Photoshop. The 680nm filter seems to leave enough residual colour to allow a little tweaking.
through a cokin ir filter as the strobe fired into it.