Digital Infrared Capture & Workflow

Clive R. Haynes FRPS

In The 'Old Days'
In common with many photographers in this 'digital age', I spent my formative years using black & white film and darkroom-based techniques whilst also enjoying parallel activities with colour transparencies and audio-visual work. My darkroom - based work caused me to experiment with infrared film, notably Kodak High-Speed IR. I found the medium to be risky, wayward, constantly 'exciting' and hugely unpredictable. There was all the business of loading the camera in the dark (using a 'changing bag' on location), focussing, then, re-focussing to the 'red spot' on the lens, fitting the opaque filter to the lens and guessing the exposure. Then back in the darkroom the film was processed using one's preferred developer and, subject to the usual oddities encountered with IR, a number of useable negatives resulted. All this gave a certain mystique to the adventure of capturing images in IR. infrared film has been around since about the 1930's - indeed, television pioneer, John Logie Baird carried out experiments with an IR video system. The movie industry used IR to shoot 'day for night' to simulate moonlit scenes in black and white films. IR therefore has a long pedigree, the scientific community have long known of its properties as a recording medium for 'thermal imaging' and the like and 'serious photographers' have enjoyed its eerie and lyrical attributes for landscape work in particular. I certainly enjoyed the very special qualities of IR and when making the change to a digital camera system I realised that this was one aspect of film-based photography that I would indeed miss.

 

What is Infrared? - A short technical excursion
The technicalities need to be brief, however but for those wishing more detail, plenty of information is published and easily available via the Internet.

'Visible light' is the small part of the very wide electro-magnetic spectrum - and as the words suggest, it's the part that human vision is able to detect. 'Visible light' is then further broken down into the spectrum of colours that we can readily identify, from red, through orange and yellow, to green and so through blue, indigo and violet. Red is at the low-frequency end with corresponding longer wavelengths of light and blue is at the high-frequency end with shorter wavelengths. infrared falls in the low-frequency section just beyond visible red. The wavelengths are measured in nanometres and for IR photography we're looking at something in the region of 700 nm and longer.

The diagram of the Electromagnetic Spectrum below gives an indication of how small an area 'visible light' represents and the position of infrared.

 
When we record the world using IR we 'reveal' how reflectivity from a variety of surfaces and objects differs from what we normally expect. For example, foliage and grasses become radiant and effervescent in appearance, whilst blue skies become near black and these special qualities lend themselves to pictorial expression. Naturally camera and lens manufacturers produce products to record 'visible light', however, in the good old days, there was a recognition by lens makers that an indicator of the focus point for IR would be useful and the 'red dot' appeared upon lenses. Look for it on modern lenses and you'll be disappointed. The 'red dot' was necessary as IR 'light,' being at a longer wavelength, focussed beyond the focal-plane of the camera and the lens required a 'tweak' to bring the scene back into sharpness.

Digital Cameras
Digital cameras using CCD and CMOS chips are sensitive to the 'near infrared'. To avoid corrupting the image an IR blocking filter is built in to the camera body. The strength of the filter varies from make to make and model to model. It's possible to shoot IR on many cameras with such a filter by using a method similar to film. It's achived by fitting an opaque filter and using a long exposure. Indeed I have done this but it lacks the speed and spontaneity of 'straight-shooting', plus there are risks of 'fogging' and flare spots. Camera Conversion I could have sought one of the few IR cameras available (at a price), which offer 'direct-viewing IR'. However, I preferred to buy a DI SLR camera and have it converted to dedicated IR use.

I chose the Nikon D70 as both affordable and readily convertible. Kits are available for DIY conversion but I preferred to send the body to a specialist. (See note at base of page). A really useful service provided by a specialist is for camera to be carefully adjusted in such a way so that whilst IR is focussed upon the array, the viewfinder remains sharp. No refocusing is necessary, you can rely upon what you see and use auto-focus with no problem.

One of the great things using a 'converted camera' is the ability to see the IR result immediately after shooting, check the histogram and feel confident.

Choice of IR Filter Depth
When deciding to have a camera converted for IR take a moment to consider the depth of the filter you need. Until fairly recently the most common IR filters were for wavelengths of around 720nm. Many specialists can now offer, as an alternative, a deeper IR filter at around 830nm.

Which one to choose? Deeper is not necessarily better - it's simply different. If you prefer a deeper filter to 'see' further into the infrared, it comes at a price. The price is one of recording an image that will be pretty well monochromatic, revealing little or no 'false-colour' characteristics. Monochrome is what one expects from IR; however, at 720nm, near-IR frequencies contribute to the attractive properties of 'Channel Swapping' and associated manipulations. So if you wish to utilise the pictorial effects and alternative colour tonalities of 'Channel Swapping' or 'Lab Color Mode', then a 720nm filter will serve you better. One of the fascinations of recording a scene in IR is that the world is revealed with a different tonal response to that with which we're familiar. In this respect no one can tell you that it's incorrect. How you record and adjust the tones and manage so-called 'false colours' is entirely your own affair and the product of your artistic judgement and aesthetic sensibility.

White Balance
For best result, it's essential to make a pre-set 'white balance' for IR. This is simple to do and here's the basic procedure which you'll need to adapt for your own camera.

Set the camera to measure the White Balance in sunlight
Point the camera to a patch of grass so that it completely fills the viewfinder
Defocus the image
Measure / set the white balance (tip: You may need to under or over-expose for this test to gain a setting)
Save as a 'Custom Setting'
Make the 'Custom Setting' your normal 'White Balance'

Setting a custom white balance helps in presenting more meaningful information for the camera-based histogram. A custom white balance will typically provide a more evenly distributed channel-to-channel histogram for each of the three RGB channels and thereby, a more favourable tonal range for initial adjustments in 'RAW' and future image management.

RAW or JPEG?
I prefer to shoot with RAW files as they offer greater flexibility and control. However, if your camera permits simultaneous jpeg images to be recorded, then use the facility, as the standard rendering of the IR image by jpeg often gives a pleasing split-tone result. This is visible both when inspecting the image in-camera and as a 'thumbnail' via the computer file-browser and of course, in 'Bridge'. This facility gives a useful indication about how the image could appear as a split-tone without 'Channel-Swapping'.

JPEG files can be used but offer less flexibility when we need to exploit the range of tones, some of which will frequently be 'off the scale' both for JPEG and the in-camera histogram display.

DI - IR Camera-Conversion Specialist:
More information about Advanced Camera Services (ACS) can be found at:
www.advancedcameraservices.co.uk
or by 'phone: 01953 889324

Click the 'continue' link below to discover more about 'Channel-Swapping'

 
Converting Your Camera to Infrared - Frequently Asked Questions - See link below
 
To view a gallery showing a selection of my infrared images, please click on the link below
 
Camera Conversion to IR FAQ's

Continue to 'Channel Swapping'

Digital infrared Photo Gallery

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