Infrared photography

[b] There is a small contribution from chlorophyll fluorescence, but this is marginal and is not the real cause of the brightness seen in infrared photographs.

[1] The first infrared photographs (as distinct from spectrographs) to be published appeared in the February 1910 edition of The Century Magazine and in the October 1910 edition of the Royal Photographic Society Journal to illustrate papers by Robert W. Wood, who discovered the unusual effects that now bear his name.

A further set of infrared landscapes taken by Wood in Italy in 1911 used plates provided for him by C. E. K. Mees at Wratten & Wainwright.

Infrared-sensitive photographic plates were developed in the United States during World War I for spectroscopic analysis, and infrared sensitizing dyes were investigated for improved haze penetration in aerial photography.

The unexpected colors and effects that infrared film can produce fit well with the psychedelic aesthetic that emerged in the late 1960s.

[citation needed] Infrared light lies between the visible and microwave portions of the electromagnetic spectrum.

[13][14]: 16  Typically, a red filter (Wratten #25) is recommended as the best compromise, which removes blue wavelengths while still passing enough visible light for focusing.

[12][14]: 16 Some photographers use orange or red filters to allow slight amounts of blue wavelengths to reach the film, and thus lower the contrast.

The majority of black-and-white infrared art, landscape, and wedding photography is done using orange (Wratten #15 or 21), red (#23, 25, or 29) or visually opaque (#72)[d] filters over the lens to block the blue visible light from the exposure.

[19][20]: 26, 38 Many manual focus lenses for 35 mm single-lens reflex cameras (SLR) and medium format SLR have a red dot, line or diamond, often with a red "R" called the infrared index mark, which can be used to achieve proper infrared focus; many autofocus lenses no longer have this mark.

[21] Without refocusing, a sharp infrared photograph can be taken by proper hyperfocal settings, which generally requires a tripod, a narrow aperture (like f/8);[citation needed] however, wider apertures like f/2.0 can produce sharp photos when the lens is meticulously refocused to the infrared index mark, and only if this index mark is the correct one for the filter and film in use.

Diffraction effects inside a camera are greater at infrared wavelengths so that stopping down the lens too far may actually reduce sharpness.

The reason for this is that any index mark is only valid for one particular IR filter and film combination, and may lead to user error.

The unexposed grains are then sensitized chemically during a second development step and produce oxidized developer, which react with dye coupler compounds embedded in the film emulsion layers to form negative images in various color dyes, respective to how the silver halide was originally sensitized for each layer.

When the slide is viewed or projected by passing white light through these stacked layers, the visible wavelengths are filtered correspondingly with the reversed colors.

[39] The external yellow filter is used because each emulsion layer in color films (both conventional and infrared) has an inherent sensitivity for short-wavelength radiation (blue and violet visible wavelengths of light) due to the silver halide chemistry.

Also in 2007, Kodak announced that production of the 35 mm version of their color infrared film (Ektachrome Professional Infrared/EIR) would cease as there was insufficient demand.

In 2008, Los Angeles photographer, Dean Bennici started cutting and hand rolling Aerochrome color Infrared film.

The trend in infrared photography continues to gain momentum with the success of photographer Richard Mosse and multiple users all around the world.

[43][44] Thus, to improve image quality and protect privacy, many digital cameras have infrared blockers or hot mirrors installed in front of their sensors.

[45] Depending on the subject matter, adding a infrared-passing filter to the lens may not be practical with these cameras because the exposure times become overly long, often in the range of 30 seconds, creating noise and motion blur in the final image.

There is no currently available digital camera that will directly produce the same results as Kodak color infrared film although equivalent images can be produced using a full spectrum converted infrared digital camera and a Kolari Vision Color IR Chrome lens filter.

While this makes such images unsuitable for the kind of applications for which the film was used, such as remote sensing of plant health, the resulting color tonality has proved popular artistically.

The ease of creating a softly colored photo with infrared characteristics has found interest among hobbyists and professionals.

[48] When the IR blocker is removed, many lenses which did display a hotspot cease to do so, and become perfectly usable for infrared photography.

For example, a very dark neutral density filter can be used (such as the Hoya ND400) which passes a very small amount of visible light compared to the near-infrared it allows through.

Wider filtration permits an SLR viewfinder to be used and also passes more varied color information to the sensor without necessarily reducing the Wood effect.

It is possible to shoot infrared but neutral density filters must be used to reduce the camera's sensitivity and the long exposure times mean that care must be taken to avoid camera-shake artifacts.

FujiFilm restricts the sale of these cameras to professional users with their EULA specifically prohibiting "unethical photographic conduct".

These cameras are generally used for building inspection or preventative maintenance but can be used for artistic pursuits as well, such as this image of a cup of coffee.