This page is part of a series of articles about digital infrared photography. You'll find link to all the segments of the IR Series in the left margin.
This segment introduces digital infrared photography, discusses the type of filter you should use to prevent visible light from interfering with the infrared capture. At the end there is a link to a collection of resources discussing every aspect of infrared photography.
All digital cameras have sensors that to some extent are sensitive to infrared light. This means that digital photography has made infrared photography much simpler than it used to be.
This article discusses selection of filters for infrared photography, and some aspects of infrared technique. In another article, I discuss the IR-suitability of interchangeable lenses and a list those that are most suitable for IR photography.
2. IR Filters
Visible light ranges from 400 nm (violet/blue) to 700 nm (deep red). Wavelengths above 700 nm and up to about 5000 nm are known as near infrared.
In infrared photography, the camera is used to capture a scene illuminated by infrared light. This may be mostly done for artistic and aesthetic effect. Some subjects (e.g. sky, water, foliage, human skin, some dyes and fabrics) will appear different when viewed in infrared light. (Note that this has nothing to do with thermal photography, where the idea is to capture heat emitted by a body. Thermal photography uses the mid-infrared spectrum – above 5000 nm. For thermal photography, you need a specialised thermal camera.)
The CCD and CMOS sensors used in digital cameras today are sensitive to light with wavelengths up to around 950 nm. However, for standard photography, capturing infrared light is not desirable, so the manufacturers put an IR-blocking filter in front of the camera's sensor. Prior to 2004, these filters used to vary in strength and efficiency (see the IR-camera page for data on older cameras). For newer cameras, the IR-blocking filter is usually efficient, and limits the sensitivity of an unmodified camera to wavelengths below 700-705 nm.
However, to capture near infrared reflected light on infrared film, or with a digital sensor, we need to stop visible light from overexposing the sensor. To do this, we use a visible light blocking filter (usually referred to as an “IR-filter”). IR-filters are mainly characterised by their pass point. This is the first wavelength of light for which the absorption is less than 50 %.
What filter to pick for IR photography is restricted by the limitations in the camera's sensitivity to infrared light, and may depend on what infrared effect you want to produce. If you pick a filter with a too low pass point, you may be unable to produce the infrared effect. If you pick a filter with a too high pass point, you may not be able to capture enough light to produce a photograph. You may need to experiment to find a filter that is fit for your camera and for a particular task.
Some infrared effects appear gradually. The sky starts getting dark already in the visible red part of the spectrum, and just keeps getting darker as you move up into the near infrared wavelengths, until it's night black around 900 nm. Other infrared effects suddenly appear, most of them around 720 nm. That includes water going dark, foliage going bright, and human skin becoming translucent and showing veins.
The table below gives the pass point for a number of popular filters. For good measure, I've also included some filters with a pass point in Red, Deep red and BVR (Barely Visible Red) end of visible light, as well as some filters with a pass point too high for even modified digital cameras.
An abbreviated notation is used in this table. The prefix “W” designates the Kodak Wratten series (e.g. W89B is Wratten #89B), the prefixes R, IR and RM is used by Hoya, RG is used by Heliopan, and B+W is used by Biermann+Weber.
The data from the manufacturers don't always add up. I've compiled the table above by using the Schott Glass (manufactures filters for Heliopan and B+W) and Hoya spectral curves and Wratten compatibility charts as reference, and placed the others according to their own Wratten compatibility charts. However this does not always match the data sheets.
The table show which filters have similar 50% IR-pass points, but it does not tell the whole story. For example: Some filters, like the Hoya R-series, have a sharp cutoff gradient, others, like the Hoya RM-series, are more gradual, and some have a weird slope. To study this slope, you need to refer to the filter's spectral curve or transmittance chart. Use the table as a rough guide – nothing more.
The IR filters fall into roughly into three categories (BVR, Weak and Strong).
- BVR (Barely Visible Red) filters include Heliopan RG665 and Kodak Wratten #70. These filters can be used to good effect if you photograph with IR-film, or with a converted digital camera where the IR-blocking filter has been removed and replaced with a BVR-type filter, in particular for false colour IR-photography. Converted bodies where a BVR-type filter has been fitted internally are often referred to as “IR Enhanced Colour” models. On an unmodified DSLR with a good IR-blocking filter, what you get is wavelengths between 650-705 nm, where the camera's response and the filter's response overlap. On an unmodified DSLR, they will typically produce a much stronger signal in the red channel than the two other channels. You may either expose right for the red channel and settle for a monochrome image, or blow the red channel and instead use the data from the green and blue channels. With IR colour film (e.g. Kodak EIR Ektachrome) or with an IR-enabled digital camera BVR, filters will darken sky, and also produce nice false colour photographs if you swap the red and blue channel. However, BVR filters will only give you monochrome images with not much infrared effect with an unmodified digital camera.
- Weak filters include the Kodak Wratten #89B, Heliopan RG715, Hoya R72, and Cokin P007. These filters begin transmitting light around 700 nm, are up to 50 % at 715nm or 720nm, and reach 90 % around 740 nm. On an unmodified DSLR with a good IR-blocking filter, you may find some data in the red channel that will let you produce a monochrome image. But the exposure time will be very long and the image will probably not be very sharp. On an older unmodified DSLR with a weak IR-blocking filter, you may be able to find data in all three channels, giving you dark sky and water, and bright foliage. Shooting on IR-film and a digital camera where the IR-blocking filter is removed, you should be able to shoot with a handheld camera and capture nice detail. You should also be able to create false colour photographs by swapping red and blue channel, but a BVR filter is probably better for false colour infrared.
- Strong filters include Kodak Wratten #87, #87C, #87B, Tiffen 87, Hoya IR80 and RM90. These filters don't even begin to transmit light until you are above the point where the IR-blocking filter in an unmodified digital camera blocks all light. This means that you need to use IR-film or a digital camera without an IR-blocking filter to use strong filters, and even then you will need a tripod. On a suitable camera, a strong filter will give you the most spectacular infrared photographs, with black sky, dark water, bright foliage, and translucent human skin. This type of filter is not suitable for false colour infrared, because the camera's red, green, and blue filters at this point is so far outside the spectrum they are designed for, that they are just pass equal amounts of infrared light.
There is no “ideal” IR-filter, but Hoya's R72 filter is very popular. This is probably because it is relatively cheap (at least when compared to some of the others), and widely available. If you are starting out with infrared, and don't know which filter to get, I suggest you start out with the Hoya R72 or similar weak filter. A strong filter, such as Hoya IR80, will cut of much more visible light and produce a more pronounced “IR-effect” – but will not work at all with an unmodified camera.
The camera's built-in light meter will work when shooting infrared. However, you may need to dial in some compensation, or bracket.
After experimenting, I've found that my camera needs a compensation of +0.7 EV when used with a Hoya R72 filter.
What the camera's white balance setting does, is adjusting the relative digital amplification of the camera's normal three colour channels (red green blue) to “balance” them so that white and grey tones really are rendered white and grey.
Of course, when shooting in the near infrared spectrum, we use a filter to block visible light, keeping only the near-infrared part of the spectrum, which is invisible to human eyes. As “white” light really is made up of equal amounts of red, green and blue components, the term “white balance” does not make sense when we're recording near infrared light.
If you are using a fairly recent unmodified camera, it will probably have an efficient IR blocking filter and the only usable channel will be the red. There is no way to change this by setting the white balance, so you can just as well leave it set to automatic or daylight. The images will have a strong red or magenta cast. To get rid of this, you need to convert it to monochrome in post-processing. Examine each channel separately, and use the channel mixer to tone down or eliminate the green and blue channels if their main contribution is noise.
If you are using an IR-converted camera, or an old camera with a weak IR-blocking filter, you should use a preset custom white balance. The norm for IR imagery is to render green foliage white or light grey. To achieve this create a custom preset white balance by taking a picture of grass or plush trees (make sure the foliage is covering most of the viewfinder. For exact procedure of creating a custom preset white balance, see your camera's manual.
In addition to providing most details in foliage after conversion to monochrome, the custom white balance preset to render foliage white will also give you the best false colour photographs if you swap the red and blue channel when you use a BVR filter on a modified camera.
You need to take the difference in near-infrared wavelengths compared to visible light into account when focusing for near-infrared photography. Wide angles tend to have a larger focus shift than lenses with long focal lengths.
To get an infrared image in focus by means of using the distance scale engraved on the lens barrel, it must be short focused (i.e. you need to focus closer than you normally would). Most fixed focal length lenses and some zooms have a mark, e.g. a red “R”, a small red dot, or some other indicator of the focus shift to apply at infinity.
On the 28-85 mm zoom depicted to the right, there are two focus shift marks engraved on the lens, representing two different focal lengths of the zoom.
If the focus shift mark is missing, focus well in front of the closest subject of interest. For a 28 mm wide-angle lens, a focus setting around 5-10 meters will be suitable for an infinity near-infrared shot. Experiment with your lenses to learn the right amount of focus shift to apply. If you are doing close-ups using bellows, a rule-of-thumb is to increase the extension by 10% to compensate for the focus shift.
If you shoot with the IR-pass filter placed in front of the camera's autofocus sensor (i.e. the filter is on the lens, and not sandwiched with the sensor), the autofocus of most cameras will work as expected when shooting near-infrared. The autofocus will lock in on correct focus for near-infrared when you half-press the shutter.
If you use a modified camera where the IR-pass filter is sandwiched with the camera's sensor, an adjustment must be made to the autofocus point for it to work correctly. Most IR-converted cameras have this adjustment done as part of the conversion.
Whenever shooting near-infrared, stopping down a couple of stops will always lead to sharper focus with any lens. The best focus is probably obtained in the f/8 to f/11 range. Attempting to shoot at large aperture (e.g. f/1.8 f/2.8) can lead to back focus (where your are focus a couple of inches in front of your subject).
Because an ir-pass filter is opaque to visible light, the viewfinder of a DSLR camera will not let you frame the subject with the filter in-place if you use an unconverted camera and mist put the IR-pass filter on the lens. One work-around is to use an accessory viewfinder in the camera's accessory shoe.
The image to the right shows a used Voigtländer Kontur accessory viewfinder. Originally made for the Voigtländer Vitessa in the 1950ies, I bought a rather tattered sample on eBay for less than US$ 20 (expect to pay a lot more for a unit in mint condition). It has a very unusual design. The centre of the viewfinder blacked out. Instead, it shows the frame-line for the field of view of an f=50 mm objective when using 35 mm film (the “35 m/m” legend on the front refers to film format, not field of view). The idea is that you look through it with one eye, keep the other eye open, and your brain combines the two images to show you the scene with a bright frame-line and excellent peripheral vision. With some experience, you should be able to use the Kontur to frame almost any focal length, by mentally adjusting for the smaller or larger field of view.
When using an accessory viewfinder on a digital camera, one need to adjust for the crop factor. If one uses the Voigtländer Kontur shown above on a camera with 1.5x crop, its field of view will correspond to 50 mm/1.5=33 mm actual focal length.
Because of the longer wavelength of near IR light, diffraction works differently. Standard diffraction limits is based upon a mid-green wavelength around 550 nm. When you capture near-IR light, with (say) a R72-filter your spectrum is centred around 850 nm. In practice this means that your running into diffraction problems 1-2 stops before you do with visible light, so a lens than performs at its sharpest at f/11 with visible light will be best at f/5.6 or f/8 when used for near-IR photography.
4. Infrared Links
See the camera page for camera conversion links.
Tutorials, Techniques & Resources:
- Ross A. Alford: Experiments with digital infrared photography
- Marco Annaratone and Claudio Ruscello: Introduction to Digital IR Photography
- Stephen R. Brown: Infrared photography with digital cameras
- David Burren: Choosing IR Cameras
- David Burren: Digital IR Choices
- David Burren: Processing infrared RAW files
- Brad Buskey: Infrared Photography Techniques
- E. Cheng: Digital Infrared Photography
- Wayne J. Cosshall: Infrared Photography
- Andrew Davidhazy: Infrared photography
- Dale O'Dell: Digital Infrared Photography Made Easy
- dpFWIW: Infrared basics for digital photographers
- Andy Finney: Books on Infrared Photography
- IRstudio.cz: Introduction to IR photography in six steps
- Jerry Kneupper: Infrared for Beginners
- Dave Larson: Infrared Conversion Work Flow
- LifePixel: Infrared PhotoShop Tutorials
- Jerry Lodriguss: Canon EOS 1DM2 and 20Da IR Daylight Tests
- Maher & Berman: How to shoot IR
- S. P. Merrill: Infrared Post Processing with Sigma Photo Professional 2.1 + PS
- Bjørn Rørslett: IR Colour Photography
- Jens Rösner: Infrared and modding
- ShotAddict: Post-processing digital IR photos
- Surveillance-video.com: Black and White Infrared Film
- Wikipedia: Infrared photography
- R. R. Williams: The fun is back for IR photography
- J. A. Wrotniak: Infrared photography with a digital camera
- Maxime Chillemi: Tumblr
- Daniella: Infrared with DiMAGE 7
- Don Ellis: Kleptography (IR enabled Canon G1)
- Chris Maher: Fine Art Infrared Photography
- Corry Lee Smith: Infrared
- David Twede: Surreal Color Photography
- Kiss Ákos Zoltán: Infrascapes
- Sue Ann Bowling: Two kinds of infrared
- Gilblom & Yoo: IR and UV imaging with the Foveon X3 sensor
- Ipac: Near, Mid & Far Infrared
- Williams & Williams: Pioneers Of Invisible Radiation Photography