The Heliopan 77mm RG 695 (89B) Infrared Filter corresponds to a Wratten 89B filter is designed to help capture images of how a subject reflects or transmits infrared light.
Infrared light waves occupy the space in the electromagnetic spectrum behind visible light due to their longer wavelengths. Many surfaces and materials react to, or emit infrared light waves differently than visible light waves, which provide the potential for photographs of subjects or subject properties that are otherwise invisible to the human eye. Such images require an infrared-sensitive medium such as infrared film or a digital photographic sensor which may be more effective when used without the infrared-blocking filters that are frequently built over them.
Conventional light sources such as the sun, photographic strobes, or incandescent lighting may be used to provide infrared illumination. However, because infrared films or digital photographic sensors can be more sensitive to the relatively higher energy and shorter-wavelength visible light those sources also emit, the effects of infrared light can be otherwise obscured. The Heliopan 77mm RG 695 (89B) Infrared Filter makes it possible to capture images of how subjects are illuminated by infrared light by blocking near-infrared, visible, and ultraviolet light waves while allowing 90% of infrared light waves 695nm or greater into the lens it is mounted onto.
This filter is constructed from Schott glass for increased optical clarity and features a thin brass filter ring to minimize the potential for vignetting while enhancing durability and jamming prevention.
