There are visible radiation (VI), ultraviolet radiation (UV), infrared radiation (IR) etc. in the sunlight reaching the Earth, and both infrared radiation and ultraviolet radiation are invisible light which cannot be seen by human eyes. The wavelength of sunlight is usually expressed in nm (nanometer). About 400nm~760nm is visible radiation, while 760nm~1mm is called infrared radiation. Furthermore, infrared radiation is divided into far-infrared radiation, middle-infrared radiation, near-infrared radiation, etc., and near-infrared radiation around 760nm~1400nm is generally effective for infrared photography. Near-infrared radiation as well as ultraviolet radiation, most strongly irradiate around 10am to 2pm during spring to summer time with high solar radiation in the warm climate like Japan.
Electromagnetic Spectrum Wavelength Chart
※Within Invisible light rays, there are X rays and gamma rays at wavelengths shorter than ultraviolet radiation, and there are microwave (used for microwave oven) and radio wave (used for television radio) at wavelengths longer than infrared radiation.
IR Cut Filter
Almost all regular cameras are equipped with an IR cut filter so that the image can be viewed like seen on the naked eye. The filter that looks blue fixed in front of sensor is the IR cut filter. This eliminates the influence of infrared radiation to reproduce the same color as human naked eye because the image sensor of camera is sensitive to infrared radiation. The cutting point varies depending on the manufacture and camera, but the IR cut filter of Panasonic AU-EVA1 used for this shooting is designed to be cut around 700nm.
EVA1 and VARICAM LT are both designed to change the IR cut filter to a clear filter. VARICAM LT can be switched manually, while EVA1 can be done by one-touch.
Infrared Movie Shooting
The Infrared shooting mixing near-infrared radiation light and a little visible radiation, has actually been done since film era by using IR filter. However, it required some experience to produce desirable image because it was difficult to manipulate both focus and shutter speed and guess the result until we develop the film. But since the effect is interesting, the IR shooting was used in many art photography works and was often used in record jackets of psychedelic rock album around 1960’s.
EVA1 can shoot infrared color movie. The best part is that it can unlock the IR cut filter with a single touch. This is an epoch-making feature. Cinema cameras in general can obtain similar effects by using the IR filter, but they cannot get the eccentric texture of infrared image because the main light of near-infrared radiation is natively cut. Also, the effect and result differs from the sensor sensitivity. In general, it is necessary to know that an infrared shooting is not possible to shoot like a regular shooting because of the following reasons.
4 Basic Knowledge for Infrared Shooting
(1) Since infrared radiation is invisible light, you cannot actually see it on set and accurately measure the exposure of subject.
(2) Depending on the difference of reflectance of infrared radiation from the substance of subject, the reflection significantly changes.
(3) In order to make interesting image, you should choose certain useful area from near-infrared radiation area that something like IR pass filter can exclusively let it pass through.
(4) Then, you need to do color swap (color shift) infrared footages in some color grading system in order to see desirable “infrared-like-images”.
In addition, shooting environment such as humidity and temperature seems to make different reflections.
Although IR cut filter OFF function of EVA1 greatly expands the possibility of infrared shooting, it is difficult to establish an attractive infrared image alone, and new creativity with experience and knowledge is required.
From here on, let’s look into the world of the new “IR Cinematography”.