Digital Infrared Photography

The world began its love affair with infrared photography back in October, 1910 when the Royal Photographic Society published, in its journal, a collection of images by American physicist and inventor, Robert Williams Wood (1868-1955).

Wood has been described as the father of infrared photography having intentionally produced photographs from infrared radiation.

His discovery finally led to the invention of infrared sensitive film. One of its early uses was in surveillance applications due to its ability to cut through haze; aerial reconnaissance teams used it during the Second World War as a method of finding camouflaged enemy positions.

For the enthusiastic amateur photographer infrared photography has opened up a whole new world of imagery. The peculiarities of infrared photography are deep black skies, bright white foliage and that magical, sometimes eerie diffused glow.

Infrared photography has given us the ability to record what the eye cannot see. As humans our eyes are sensitive to a limited band of wavelengths, between 400nanometres (the blue spectrum) and 700 nanometres (the red spectrum) known as visible light.

Infrared light-waves on the other hand stretch beyond this red spectrum and travel on, right up to microwaves, past 10.000nm. The infrared spectrum is split into three sections; Near Infrared, Far Infrared and Thermal Infrared.

As infrared photographers it’s the near infrared spectrum that interests us the most; the ~700 – 900 nanometre range. The far infrared spectrum, above 900nm, deals mainly with heat waves, which is beyond the range of what a modern day digital camera can capture.

With a capable digital infrared camera many scenes, which under normal lighting conditions maybe considered ordinary to some, are often transformed when captured in infrared. With digital infrared there are a number of different ways in which the final image can be processed giving the photographer complete artistic control.

What type of camera will I need?

The sensors fitted in all digital cameras have the ability to capture a large portion of the electromagnetic spectrum, from the ultra-violet (400nm) right up to near Infrared (900nm). However, because infrared radiation contaminates images taken under normal “visible light” conditions all modern day digital cameras are fitted with a special infrared blocking filter, called a hot mirror or a cut filter. This filter lets in light from the ultra-violet spectrum (400nm), but blocks out light from the infrared spectrum, above 700nm.

Therefore, in order for us to capture infrared images we must reverse this process and block out all visible light below 700nm. To do this we replace the cut filter with an infrared filter. If this modification is made then any digital camera on the market will be able to take infrared images.

However, here lies the problem! The process of removing the hot mirror filter is tricky and needs to be handled by a qualified technician; otherwise you run the risk of harming yourself or damaging your camera, maybe even both!

On the other hand, all is not lost; some digital cameras are quite sensitive to infrared wavelengths even with their hot mirror filters still firmly in place. One such camera is the renowned Olympus C-2020z, a simple point and shoot digital compact camera, which has a 2.1 megapixel sensor. By placing an opaque filter, such as a Hoya R72 in front of the lens, infrared photography becomes possible. In fact, some of the best performing cameras for infrared photography have been those produced in the early days of digital photography, when digital camera manufactures were less concerned with infrared contamination.

The sensor used in the C-2020z was manufactured by Sony; this sensor was also fitted to a number of other cameras offering the same 2 megapixel capabilities, notably Sony’s own S50 and Nikon’s early Coolpix range; 700/800 and 950. All these cameras now have legendary status amongst infrared photographers and as a result are becoming quite collectable and increasingly difficult to get hold of.

If you have your sights set on something a bit more versatile, but without resorting to a full blown infrared conversion, take a look at any of the 6 megapixel Nikons; D40 D50 and D70. Although these cameras won’t allow you to make hand-held infrared exposures they are pretty much sort after as infrared sensitive cameras.

If you happen to own a Canon DSLR then I’m afraid you will have to have it fully converted to shoot infrared. The only model that is practically sensitive enough to capture infrared image without the conversion is the 3.2 megapixel D30, not to be mistaken for the later 8.2mp 30D.

At the end of the day the camera is but a tool, a means to an end.

What IR filter should I use?

If you plan on using a none-converted camera to capture infrared images the filter you choose will largely depend on your lens choice? Personally I would recommend something like a wide-angle zoom, such as an 18-70mm. This type of lens makes it practical for you to cover most subjects, from landscapes to portraits and in some cases, depending on lens construction, close ups or macro.

Not only do infrared filters come in different sizes, but they come in different strengths too. Remember, these filters are designed to block out light at different wavelengths. The weakest infrared filter you will find in the Cokin (P007) infrared filter. This filter blocks out light-waves below 650nm, but as we have already established, near infrared light starts at around 700nm, therefore, the Cokin filter will still allow a fair portion of visible light through. This is fine if you want coloured infrared, but the majority of digital infrared photographers are aiming for a more traditional look.

Nonetheless, the most popular infrared filter, by far, is made by Hoya, the R72 infrared filter. This filter will block out light-waves below 720nm. Because these filters are opaque the resulting RAW files have a reddish brown cast to them, which I will explain more about later. The reason I mention it now is because the Hoya R72 is the preferred filter for those photographers who wish to render their infrared skies blue; again, a subject I will touch upon in a moment.

If you want to capture a more traditional looking infrared image, one that is stripped entirely of colour, then you will have plump for a stronger blocking filter; above ~750nanometres.

Do I have a personally favourite? No, not really – I use all three filters on different cameras. I’ve found that certain cameras perform better to one type of filter than they do to another. For instance, I use a Hoya R72 on my Olympus C-2020 and Nikon D50, I will use a 750nm infrared filter on my Canon G9 and I canalised my old Cokin P007 filter to convert my Nikon Coolpix 995 to infrared. Three entirely different filters, but suitably matched to the cameras I use them with.

Exposure, Metering  and Focusing

The downside to using any infrared filter over your lens is speed.

Because the infrared filter covering your lens is trying to block out all visible light and the internal hot mirror filter is effectively blocking out all near infrared light the amount of actual light hitting the cameras sensor is minimal. Consequently, shutter speeds times will be painfully slow. Even on a bright sunny day, working with a relatively sensitive camera, such as the Nikon D50, your shutter speeds are still going to be in the region 2 or 3 seconds at f8, with some cameras, considerably more! Obviously some kind of support is going to be needed whatever camera you use?

Some photographers might see this as a problem, others not. However, I have to mention it, this isn’t your only problem! Composition of your subject has to be made without the infrared filter in place, for the simple reason, the filter is opaque; you can't see though it.

To make your exposure you will need to fix your camera firmly to a tripod, compose your shot in the normal way and refit the infrared filter before taking your shot. This may sound simple enough, but after awhile it does become tedious and irritating. Anything other than landscapes or objects that don’t move is pretty much out of the question!

Because our camera lenses are designed to work best under normal lighting conditions and not under infrared radiation, there’s also a slight shift to your point of focus. Some older, manual focusing lenses, will have a red infrared focusing dot to compensate for this, newer ones may not. To overcome this focusing discrepancy it’s wise to stop your lens down to a small aperture thereby maximising your depth of field.

Modern day digital cameras all have very good metering systems; even the very early digital compacts were quite good. Nonetheless, when shooting in infrared the last thing you want to do is blow those highlights. For this reason I would advise you under exposure your images by at least 1/3^rd of a stop.

Regardless whether your camera has been fully converted or not, to get the best possible results from your images, you will need to shoot everything in RAW; this isn’t an option, but a necessity! Why? Because RAW files contain more information, which will allow you better control over the final exposure and complete control of your white balance.

If your camera doesn’t allow for RAW captures, most digital compacts don’t, confine your images to un-compressed tiff files. Un-compressed tiffs from the Olympus C-2020, Nikon Coolpix 700/800/950 and the Coolpix 995 when processed correctly hold enough information for you to make A3 prints.

If you only ever use your camera for taking infrared images you may want to consider having the hot mirror filter completely removed and an infrared filter put in its place. The benefit of this procedure is easy to see; Normal shutter speeds, no messing around with filters, use any lens you wish, no tripod to carry around and no focusing issues to deal with.

If you only ever use your camera for taking infrared images you may want to consider having the hot mirror filter completely removed and an infrared filter put in its place. The benefit of this procedure is easy to see; Normal shutter speeds, no messing around with filters, use any lens you wish, no tripod to carry around and no focusing issues to deal with.

In the past I was quite happy to shoot with the filter screwed to the lens, but once you have used a fully converted infrared camera you won’t want to go back to using anything else.

Selecting Your White Balance Point

OK, now comes the important bit, selecting your white balance.

Whether you own a fully converted digital infrared camera or you use an infrared filter over the lens, your images will take on a colour cast. A weak infrared filter similar to the Cokin filter will produce a distinct red cast; a stronger infrared filter above 750nm will appear monochrome, which leaves the Hoya R72 type in the middle with a reddish brown cast. Before we can get our images looking anything like the infrared images taken on film, we need to get rid of the colour cast.

There is two possible methods by which this can be achieved; in camera (if your camera allows it) or with software. I will deal with in camera white balance first as this is the easiest method to explain.

Go to your cameras white balance menu, from here you can choose from Auto, Sunny, Cloudy, Incandescent, Florescent; find the option that lets you choose a “Custom” white balance.

What happens here is the camera will let you record an image under the prevailing lighting conditions you are working in.

For Example; if you happen to be taking a landscape picture choose your “Custom” white balance from a patch of grass in full sunlight, take the shot and the camera will save and store this image as your custom white balance. If the light changes at any point during the day, simply record a new white balance and save it. You will see the efforts of your white balance setting on your cameras viewing screen as you take your shots.

Alternatively, you can leave your camera’s white balance set on “Auto” and then, when you open the image in your RAW conversion software; simply choose a white balance point from there.

This shot shows an infrared image with no alterations, recorded directly to my compact flash card. As you can see the image has picked up a strong cast from the ~750nm filter, but it's still showing a full range of tones. To correct the cast we need to select a white balance point from a pixel within the image using the white balance point eyedropper.

I made my selection from the white patch of grass at the bottom of the frame. I could also have picked a white tone from the side of the building or from the handrail, to the right of the frame.

Here we see the image after the white balance point has been selected.

And finally, converted to monochrome with a medium contrast curve applied. You may wish to add a touch of grain, maybe a little Gaussian blur to give it that authentic (film) infrared look.

You can, by spending some time with your RAW conversion software, begin to understanding what tones will give you the best results. This will, undoubtedly, pay dividends in the long run. With practise, selecting your white balance point will become second nature, in doing so; will have a marked improvement on your final infrared images.

False Colour Infrared and Channel Swapping

Personally I prefer to process my digital infrared images to have a similar look and feel close to what was achieved when using conventional High Speed Infrared Film. These were monochrome images with a fair amount of grain, slightly diffused and a little on the soft side. However, there are some digital infrared photographers, who choose to display their work by leaving them in colour. As with any type of photography the option to shoot monochrome or colour will depend on the subject matter, you still have that choice.

How much colour you choose to leave in your infrared images will depend on you, the type of infrared filter you use and how you process the images. As we’ve already established, the weaker the infrared filter the more visible light it will let through. A good compromise is the R72. This filter will block out a fair amount of visible light, but not all of it, some visible colour will still creeping into your final image. After all, you can still convert your R72 infrared images to monochrome later, should you wish?

If you are considering have your camera converted? Choose the type of filter you want fitted wisely; mistakes made now are not easily rectified later. Having a 720nm filter fitted inside your camera is possibly the best choice.

Perhaps now is a good a time to introduce you to the benefits of “Channel Swapping”. In simple terms, our digital cameras capture images that are made up of three colour channels, Red, Green and Blue, also known as RGB. These three colours or channels are used to reproduce the colours we see on-screen and in print.

By altering the value of one or more of these colour channels, will effectively, alter the colour of your image quite drastically. However, with digital infrared photography we can use this to our advantage.

Here’s How: After selecting a white balance point your image might still show a slight orange/reddish cast usually in the sky area with your foliage showing minor signs of a cyan/blue tinge. This is perfectly normal for an R72 filter. By using a software programme such as Photoshop™ we can gain access to these three colour channels through the Channel Mixer and swap them over. By swapping the Red source channel for the Blue and the Blue source Channel for the Red we end up with a totally different looking image, more akin to a frosty winter scene than a psychedelic sunset!

This is how it works in practise: With Photoshop™ running and your chosen image open select - Image> Adjustments> Channel Mixer. This will open the Channel Mixer dialogue box, the default settings should read as:

Preset: Default. Output Channel: Red - Source Channels: Red 100%, Green 0%, Blue 0%.

Change the Red Source Channel to 0%, Green 0% and Blue to 100%.

Without leaving the Channel Mixer dialogue box change the Output Channel to Blue and set the Red source channel to Red 100%, Green 0% and Blue 0%.

Click the OK box when done.

Your channel swapped image should look something like this?

High Dynamic Range (HDR) and infrared, a match made in heaven

Infrared images don’t have to be contained to single exposures. You can create HDR images by bracketing 3 exposures over a 4 stop exposure range, -EV2 to +EV2. The resulting three exposures are then blended together using specialist software to create a High Dynamic Range (HDR) image. High Dynamic Range images contain a range of values from the deepest shadows to the brightest highlights. The only problems being, HDR files exceed the reproducing capacity of low dynamic range media such as monitors or prints.

To show this extra detail on screen or in print the HDR image needs to have its tonal values mapped so that they fit in the limited tonal range of your monitor or printing device. This process is known as “Tone Mapping”. Tone mapping can be handled by using the same software used in creating the HDR image. With patience and practise High Dynamic Range images can look spectacular, but be careful not to over do the effect otherwise your images will look cartoonist and messy.

If you use this technique simply as an aid to control your exposure, you won’t go far wrong.