Infrared photography with a digital camera

Infrared Photography With a Digital Camera

● What's so different about IR? ● Camera and filter ● IR filter summary ● Exposure setting ● Fogging ● Focus ● Postprocessing ● Web resources

Image samples:

● Olympus E-10 and E-20 with Hoya R72 ● Olympus C-5050Z with Hoya R72 ● Olympus C-5060WZ with Hoya R72 ● C-3000Z with the Wratten #70

It was more than thirty years ago when I last experimented with photography in infrared. Too much hassle: special film handling, black-and-white processing, inability to evaluate results (and adjust settings) until the whole roll was exposed and pictures were printed...

Now this has changed. Due to the arrival of digital photography, we can take infrared pictures whenever we please, mixing them with "normal" ones, and see results on the spot, tweaking the settings to our hearts' desires...

All depends, of course, on how your camera sensor array reacts to the infrared — and, depending on the filter you are using, to the far red end of the visible spectrum.

Olympus C-5060WZ, Hoya R72 filter

What's so different about infrared?

At the first glance, a monochrome picture taken in infrared may look similar to just another black and white photograph. And then you start seeing differences: objects which are bright in visible light (like sky) look dark here, while some of those which are "normally" dark (green foliage) acquire a bright glow. An unusual and eerie feeling.

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Infrared photography with a digital camera

This can be explained with the graph at the right, showing the percentage of light reflected off various materials at various light colors (wavelengths). The height of the curves to the left of 600 nm shows how bright these materials are in visible light; to the right of 700 nm — how bright they are in infrared.

The most dramatic difference between the visible and infrared spectrum is in case of foliage: it does, indeed, become very bright in infrared; very much like you can see in my photographs shown here.

(Source: Kevin Frankel at al., Concealment Of The Warfighter’s Equipment Through Enhanced Polymer Technology, 24th Army Science Conference Proceedings, Orlando, FL, 2004)

To answer the question briefly: photographs in infrared show quite unusual tonality, different than that to which we are used, and this may make them esthetically pleasing, at least in many cases. Which, of course, is a matter of taste.

Camera and filter

First, you need a digital camera. As far as I know, all of these have a special infrared-blocking filter in front of the light-sensitive CCD array, as the IR light degrades the visible-light image quality (and the CCD itself reacts to wavelengths up to 1000 nanometers and even longer). The question is how much of infrared will the filter let through.

The old venerable Olympus C-2000/C-2020 (but not the '2040!) and Nikon 950 were quite permissive here, but the 30x0, and 40x0 series seem to let just enough of IR light through to be suitable for infrared photography; the C-5050Z, C-5060WZ, E-10 and E-20, although requiring quite long exposures, also offer a workable solution.

For example, using the Hoya R-72 filter on the E-10, E-20, C-5050Z, or C-5060WZ requires exposure adjustment by about 11 EV (F-stops), or by a factor of 1500 to 3000. As a matter of fact, I would classify these cameras (which I have all used a lot) as barely usable for infrared shooting (on the other hand, I am getting very nice IR results from them, anyway). For comparison, the C-2000 needed only a 7 EV adjustment, being about 20 times more sensitive.

For other cameras, check for yourself before investing into any filters. You may also find data on selected models at Jen Roesner's site.

Some of the Sony cameras (Sony DSC-F707/717/818 in this number) allow you to move the anti-IR filter out of the light's way; unfortunately, Sony went to great measures to make this feature unusable in daylight, as it is supposedly making some clothing partially transparent to infrared. (I would also like to turn Sony's attention that the big lens in the '717 can be used to hurt babies and puppies.)

Ironically, digital SLRs (except for the E-10/E-20 by Olympus) do not allow you to use the LCD monitor for picture preview and composition. You have to compose without the filter (using a tripod, of course), then put the filter on and shoot blind. If you have a digital SLR and intend working in infrared, you will be better off getting an inexpensive non-SLR model specifically for infrared. You need a small backup camera anyway.

Some people modify their cameras by removing the anti-IR filter (sometimes replacing it with a glass plate of equal thickness). This is a tricky operation, but it will usually increase the camera's IR sensitivity dramatically. Obviously, the camera's performance in visible light will be degraded, and your warranty will be voided.

Then you need an infrared filter. You can buy these from any dependable mail-order supplier, like B&H Photo.

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Infrared photography with a digital camera

Various filters may differ in the visible light cut-off point (see the table below). The Wratten #89B (available as Hoya R72), with the light transmission falling down to 50% at 720 nanometers, seems to be most popular and gives the greatest chance of success. The darker #87 or #87C may or may not work, depending on the camera, while the almost-IR #70, while allowing for shorter exposure times, does not provide the eerie Woods effect on greens.

You also need a way to attach the filter to your lens. This is not a problem with SLR and digital-finder models, but digital compacts may pose a problem. WIth very few (like the Olympus C-5060WZ) you can do it directly, as the lens is threaded; with others (actually, all other compacts on the market) you will need a lens adapter tube, like the 41-43 mm CLA-1 attachment for the Olympus C-5050Z (plus a step-up ring).

A tripod is essential. For the #89B (R72) filter and Olympus E-10/E-20 and C-5050Z I'm getting exposures of 1-2 seconds or more at the lowest ISO setting.

Olympus E-20, Hoya R72 Olympus E-20, Hoya R72

IR filter summary

Here is a brief comparison of the infrared filters, including those made by B+W, Hoya, and Tiffen as of November, 2004, Those generally available in glass (as I've checked at B&H in November, 2004) are marked in bold. Some are available as gelatine foil only.

The filters are listed in order of increasing "blindness" to the visible light. The "0%" column shows the wavelength below which the filter has zero transmittance (i.e., lets no light through), while "50%" — the wavelength at which the filter blocks half of the incoming light (50% transmittance).

Wratten Schott B

+W Hoya Tiffen 0% 50% Remarks

#25 OG590 090 25A 25 580 nm

600 nm Really a red filter

#29 RG630 091 - 29 600 nm

620 nm Dark red

#70 RG665 - - - 640 nm

680 nm Very dark red

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Infrared photography with a digital camera

#89B RG695 092 R72 - 680 nm

720 nm Almost "black", but not

quite

#88A RG715 - - - 720 nm

750 nm I've never seen this one

#87 RG780 - - 87 740 nm

795 nm Cuts off all visible light

#87C RG830 093 - - 790 nm

850 nm Usually called "black"

#87B RG850 - RM90 - 820 nm

930 nm Expensive! $250 & up!

#87A RG1000 094 RM100 - 880 nm

1050nm Blocks even some of

infrared

The data above is quoted after W.J. Markerink. For those who would like to have a closer look at IR filter transmittance, here is a graphic representation:

The graph shows the transmittance of various filters as a function of the wavelength. It is based on data by Paul Repacholi (Curtin University of Technology, 1992), posted by W.J. Markerink and also by Eric Cheng.

The logarithmic scale is used here, as it fits the problem better: differences, say, between 1% and 10% are by far more meaningful than those between 91% and 100%.

It can be clearly seen that #89B (R72) still allows through some of the far red (just below and around 700 nm), #87 starts only around 740 nm.

Just a reminder: the human eye is sensitive to wavelengths up to 700-720 nm or so.

Because the anti-IR filters in digital cameras block most of the infrared, even slight differences in filter transmittance may have strong effect on results (and exposure). Therefore two filters listed as equivalent in the table above may deliver slightly different results on a given camera.

Recommendation: I believe the most useful, general-purpose IR filter for digital photography is Hoya R72 (#89B). It blocks visible light well enough (if not entirely) to provide a well-pronounced IR effect, while still allowing for non-exotic exposure times. This filter should work fine with most of mid- to high-end amateur digital cameras (your mileage may vary, so check with someone who tried it on your camera). The small amount of visible (far red) light which this filter lets through does not affect pictures enough to spoil the IR effect, while coloring your images red (or purple), therefore they need to be converted to monochrome in postprocessing.

The #87 filter is more expensive and more tricky. Many digital cameras will not be able to "see" through it, while some others may work — again, check with their users. (I have seen very pleasing images from the Olympus C-4000Z, using this filter.)

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Infrared photography with a digital camera

Exposure setting

All digital cameras I know measure the light through the lens: non-SLRs use the CCD itself to do that, while SLRs have dedicated, metering sensors for which some of the light used for viewing is diverted.

This means that you can, more or less, trust the automated exposure metering — as long as the metering system is capable of doing its job at the very low light levels due to the filter density. It should be: a typical IR exposure on Olympus cameras I've tried with the R72 filter is about one second at F/4 and ISO 100, this corresponds to exposure value of EV 4, while most cameras can cope with EV 0 or close.

More exactly, I like to override the auto settings with some (-1/3 to -1 EV) exposure compensation, to keep highlights from burning out. In any case, after your first IR session you will know how much exposure compensation do you want to apply with your particular camera/filter combination.

Generally, your exposures will be quite long, because an IR filter lets through less than 0.1% of the incoming light. For example, the Olympus E-10/E-20 and C-30x0, C-40x0, and C-50x0 series require exposures somewhere between 11 and 12 EV values (that is a factor of 2000-4000x) longer than in visible light. This brings the shutter speeds from, say, 1/500s up to 4s on a sunny day, quite a difference. Not only this necessitates the use of a tripod, but if the air is not quite still, you will not avoid a blur in the foliage, grass, water reflections, etc., not to mention any humans in the picture. (The latter effect can be quite useful.)

While some, other models, especially older ones, may be more sensitive to the infrared, do not expect a factor of less than 500 or so (i.e., 9 EV).

Note to SLR users: remember to close the eyepiece shutter, otherwise the visible light, entering through the eyepiece, scattered off various surfaces, may ruin your infrared pictures. Users of non-SLR cameras, obviously, do not have to worry about this.

Fogging

Regardless of that effect, certain camera models (SLR or not) may still exhibit some fogging, or image areas with extra exposure. This, I suspect, may be due to some light scattered from inner surfaces of the camera body and/or lens; perhaps the black coating of those is not black enough in infrared? Sometimes this happens to all cameras of a given model, sometimes — just to a particular specimen or a particular lens. Camera makers are not worried about this: very few users ever venture into the IR realm, and this is a mass market after all. There is no way to avoid this problem; once again, check an IR filter on your camera before buying.

Focus

The focal length of your lens (and therefore the proper focus setting) depends on the wavelength. Lens makers try to keep that dependency to a minimum (achromatic lenses), but only within the visible light spectrum. As soon as you are into infrared, the chromatic aberration curves go astray.

Because autofocusing in most digital cameras is done through the lens, the focus shift is automatically taken care of. Therefore it may be safer to let the camera focus — as long as it is capable of doing that at EV 4 and below. Most cameras are, but not very reliably, so I would recommend taking more than one picture, every time forcing the camera to re-focus. Doing that, no IR-related corrections to focusing are necessary.

Setting the focus manually may not work any better, as the distance scale corresponds to focusing in visible light. If in doubt, try setting focus a little closer than the actual subject distance: at 50 mm equivalent focal length use about 4-5 m instead of infinity, but this actually depends on the particular lens.

My early experiments, setting the Olympus E-10 to infinity, resulted in very unsharp pictures. If you want to focus manually, you'll have to do a series of test shots.

In either case, the depth of field may help masking the lack of proper focus to a large extent. In case of problems, try to use wide zoom settings and shoot in aperture priority at F/8 or so; this may help.

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Infrared photography with a digital camera

Postprocessing

The response of red, green, and blue photosites in the CCD, and therefore the color image recorded by the camera, is the result of a subtle play between the transmittances of three (!) filter layers involved here: (1) the IR filter mounted on the lens; (2) the anti-IR filter in front of the CCD; (3) the tiny red, green, and blue filters in front of each photosite of the sensor.

No wonder that the (false) colors of an image shot in infrared will vary wildly from camera to camera, and from filter to filter used.

While some cameras, especially when used with filters darker than #89B, may come up with color images which some may find pleasing, in most cases the images will have a very strong red or purple-red tint. This is certainly true of all Olympus models I have tried or used, but not only. The effect also depends on the sensor gain (ISO setting).

Therefore usually you would like to translate your IR pictures into gray scale, i.e., to black-and-white (or sepia) monochrome.

Depending on your postprocessing program, you can do it by desaturating the image, or changing its mode to 16-bit monochrome, or applying a duotone filter. Then you may tint your monochrome picture to sepia or something else.

Retaining some color information

Your infrared images do not have to be monochromatic (like black/white or sepia). There is some color information in the image file, and while it has nothing to do with reality, it may be used to generate quite pleasing images. The easiest way to do that is to split your image into individual RGB components, adjust each separately, and

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Infrared photography with a digital camera

then recombine them.

Here is an example of such a treatment, borrowed from my Olympus C-5060WZ infrared sample page, where you may find more details on how the image was postprocessed.

Olympus C-5060WZ, Hoya R72, after color layer manipulation

Image noise

Some photographers (especially those who never printed anything above 4x6" from their film cameras) are allergic to noise in digital images. Others, however, are so used to the large grain in infrared films, that they consider the noise a part of the "infrared look" and want to emulate the effect in the digital medium.

Well, you cannot please'em all. If you dislike noise in your IR images, tough: it will be there. You will have much more of it than in "regular" color pictures. If you find the noise objectionable, it can be removed quite well with use of the Neat Image program. It does a very good job, and has a wide range of available adjustments.

In the opposite direction, to emulate the IR film grain effect, some writers recommend adding artificial noise in postprocessing. I'm not very happy with that technique, preferring rather to intensify the natural noise pattern of the CCD. This can be done by setting the CCD sensitivity to the equivalent of ISO 400 (or higher, if your camera allows it). As a side effect, you will also reduce the exposure time, which usually is a good thing.

To make the noise more visible, you may also underexpose your pictures by one or two EV, and then stretch the tonal range in postprocessing to recover the shadows and highlights; this will also amplify the noise considerably. This technique takes less to apply than to describe, see an example below.

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Infrared photography with a digital camera

Olympus E-20, Hoya R72, underexposed and re-equalized A 1:1 sample from the image at the left

In most of my infrared images, however, I'm happy with the amount of noise as it is, with no need to reduce or to increase it.

Almost infrared: a deep-red filter

The easily available Wratten #29 (B+W #91) deep-red filter will also deliver quite dramatic monochrome effects (although not as strong as these obtained with the #70). But, importantly, with the light loss of only about 8x (3 EV) it can be used safely without a tripod.

One of my Readers reported success using such a filter for IR photography. To get rid of the visible-light component, he would remove the red layer of the RGB image, leaving only the green and blue layers. As these are virtually blind to red, only the IR input would be left.

While this might work with some cameras (he used a non-SLR Nikon), my experiments with the Olympus C-5060WZ ended up with negative results. The green and blue image layers, as dark as they were, did not show any Woods effect. This indicates that their IR sensitivity is even lower than that for the red light. I've tried the same approach with a #70 filter, also to no avail.

A deep-red filter may still provide very nice monochrome images, as long as you do not have to have the Woods effect. I'm using it from time to time, and the extra advantage is that with the exposure multiplier you can get away shooting from hand. Some examples are shown in my C-3000 near-IR sample page.

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Infrared photography with a digital camera

Web resources

Back in 2000, when this article was originally posted, there was a scarcity of any IR information on the Web (the first three items on the list below being notable exceptions). With the popularity of digital medium, however, there is more information available now. Here are pieces which attracted my attention.

● Clive Warren's Infrared Photography FAQ — a good introduction to the subject, covering both film-based and digital aspects; ● Jeremy McCreary's Infrared Basics for Digital Photographers — an excellent article on the subject at his dpFWIW digital photography site; ● Eric Cheng has a rich IR section on his photography site; ● Digital Infrared Photography Made Easy, an article at Apogee Photo; ● Experiments with Digital Infrared Photography by Ross Alford is a nice article with some pointers on obtaining interesting pseudo-color effect by image layer manipulation. ● Jen Roesner from Germany has a whole site dedicated to digital infrared pgotography, including a comparison table of various cameras' IR sensitivity.

Check also The Beauty of Infrared page in my Gallery section.

Copyright © 2000-2005 by J. Andrzej Wrotniak. Reprints and links permitted with proper credits.

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Infrared photography with a digital camera

Posted 2000/06/12, last updated 2005/02/05

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