I have always had a fascination with infrared photography for as long as I can remember. I started out with my first film camera when I was only just a teenager, I was drawn to photography like a magnet at a very young age and in the years that followed I was fortunate to be able to experiment with film processing and printing in a make-shift darkroom at home. I progressed from a make-shift darkroom to something permanent, from regular black & white to infrared, lithographic and then both colour negative (C41) and colour positive (E6) processes. Upon turning sixteen I went to work in the darkroom of a busy wedding photography business. That was all thirty-five years ago.
I think the fascination with infrared for photographers back in the heyday of film went hand in hand with our preoccupation with black & white. Shooting in black & white was as much a necessity as a desire, both the film and the subsequent processing was a lot cheaper than for colour and it was a normal progression to want to experiment with home processing. That whole process of taking photographs, developing the film and hand-printing the results was as natural then as the whole process of capturing images, editing them in software and publishing them to the internet is today.
Shooting infrared using a film camera was relatively straightforward. Infrared films were commonly available alongside regular film stock at my local photography supplies shop, as were the blackened glass infrared filters that you needed to fit to the front of your lens. The trickiest part was to get accurate focus because infrared radiation focuses to a different point than visible light. It helps to appreciate now just how popular infrared photography really was back then because all the mainstream lens manufacturers printed an index mark on their lenses to aid infrared focus adjustment.
Thirty-five years on and I still love to shoot infrared images. However, digital technology has not made it much easier to capture them, in fact, in some respects it has made it harder!
The Switch to Digital
The first problem to overcome is finding a digital camera that can record infrared images. What I have learnt is that the imaging sensor inside a digital camera is so inherently sensitive to infrared light that camera manufacturers go out of their way to prevent any infrared light from reaching the sensor at all. They do this by placing a semi-reflective filter called a hot mirror in front of the sensor which reflects back infrared light and also helps to keep the sensor cool. These hot mirrors are almost always permanently fixed into place at the factory, so, if you want to shoot infrared images, you need to perform major destructive surgery on your camera in order to remove it.
There are people who do this kind of destructive conversion work professionally, some better than others, and it is always expensive. The conversion process itself is very time-consuming, complex and risky; it will also immediately void any warranty that the camera has. I have braved these risks several times and had three converted digital cameras over the years.
It is very common with these kinds of camera conversions to put an infrared filter in place of the hot mirror so that you can shoot infrared straight away without the hassle of having to fit infrared filters onto your lenses. I would advise very strongly against a converted camera such as this. The first two cameras I owned turned out to be dust traps, dust particles would get trapped between the sensor and the infrared filter that had been fitted. Eventually the camera is rendered unusable because of the dust build-up which is impossible to get rid of without taking the camera completely to pieces.
For the third converted camera I learned from my mistakes and insisted on no infrared filter. Such cameras are marketed as full spectrum conversions and you will need to fit an infrared filter to your lenses to capture infrared images.
Not all cameras are built with a permanently fixed hot mirror. If you want to avoid the cost and risk of a camera conversion, there are other options out there even though they are few. Sigma cameras are – to the best of my knowledge – the only mainstream camera manufacturer today which produces a removable hot mirror solution, and it is for this reason that the Sigma SD Quattro has become my main camera for infrared photography since its release just over a year ago.
The hot mirror on the SD Quattro can be removed by just using your fingers if you are dextrous or else you can use a simple pair of every-day tweezers. With just a little practice you can feel confident doing this operation in just a few seconds when you are out on location, which is fantastic as you can take just one camera with you for shooting both traditional and infrared images.
Infrared radiation is not just one wavelength but a whole range of wavelengths beyond the visible light spectrum and there are a variety of infrared filters that you can use. Filters targeting shorter wavelengths will tend to also let through some level of visible light and it is worth taking the time to experiment with different filters to find the results that you prefer. All the infrared images in this article were shot using a 720nm filter which is a common choice and considered ‘middle ground’ for infrared photography. I have tried longer wavelength filters in the past and, while the images may be purer in infrared terms, the exposure times are longer and your camera will have a harder time providing you with a decent live view from which to focus.
In terms of filter brand, I have found it really pays to buy the best quality you can afford. Whatever you put in front of a lens is going to deteriorate the quality of the image. I extensively use a filter holder system and obtained a compatible 100mm square 720nm infrared filter. This setup means I need just one filter for all my lenses which can save both time and expense in the long run.
Effective resolution and colour vs monochrome
Because of its wavelength, infrared radiation is mostly captured by those photosites in a digital sensor that are sensitive to red light. Cameras with a Bayer sensor will record some minor light levels in their green and blue channels but Sigma Foveon sensors will record none. This is a testament to the accuracy with which Foveon sensors record colour as there is almost no perceptible leakage into the non-red channels unlike with a Bayer sensor.
However, when it comes to resolution, both types of camera sensor have only a minority of photosites sensitive to red; the vast majority of photosites in a Bayer sensor are sensitive to green while the majority in a Sigma Foveon Quattro sensor are sensitive to blue. The implications of this are that infrared images are recorded with much less effective resolution than a full colour image would possess – there is a huge imbalance in the colour information that is captured too. I personally find that infrared images tend to work best when rendered as monochrome artwork rather than colour, and this is far more in-line with my memories of infrared from my days in the darkroom. Unlike colour infrared images which look alien, monochrome infrared images for me can be almost believable – they can resemble a snow-swept landscape combined with the dramatic skies of a black & white image shot with an orange or red filter.
Focus and lens choice
Focusing infrared with film cameras was never straightforward, but obtaining focus with digital cameras is simple. Even autofocus is likely to work if light levels are sufficient. For manual focus, which is my preference, using a mirrorless camera with an EVF and focus magnification such as Sigma's SD Quattro eliminates all the guesswork.
In terms of lens choice for infrared photography, it is important to bear in mind that all modern digital camera lenses are designed for the visible light spectrum and not infrared radiation. There is a common phenomenon when shooting infrared images called infrared hotspots, which is where a central circle of light that is visibly higher in exposure appears on captured infrared images. Although it is possible to remove these hotspots in post production, it can be time-consuming to do so – it is best to avoid the hotspot in the first place. What you will find from experimenting is that some lenses are more prone to hotspots than others and that choice of aperture has a significant effect as well.
I don't want at this point to give a view on specific lenses because I think it is very important as photographers that we try for ourselves and determine which results work for us as individuals. A lot depends on your choice of subject, what your depth of field requirements are, and whether you are ok to use a tripod or really need hand-held. As a general rule I have found that lenses more prone to hotspots tend to be zoom lenses in the wide or wide-to-medium focal length range. Prime lenses tend to perform best. If you have a lens that is prone to hotspots you may still achieve acceptable results if you use wider apertures since hotspots become more defined as aperture decreases.
One more thing to mention which is related to lenses and aperture settings is diffraction. It is a problem in traditional photography at very small apertures but it is an even bigger problem with infrared radiation. So, you will need to use wider apertures to get the same quality results as you are used to. Again, I cannot stress enough the benefit of experimentation to know the limitations of your equipment ahead of an important shoot.
Image capture and post-processing
I have not mentioned it yet but I always shoot in raw with all my cameras, including the SD Quattro. Even though it allows me to shoot in DNG for convenience, I prefer to shoot in raw and use Sigma's Photo Pro software (SPP) to perform the initial conversion to non-raw format. For infrared, I don't perform any specific editing in SPP, but I prefer its conversion accuracy compared to in-camera.
Following are my own personal processing steps for infrared images that I have shot with the Sigma SD Quattro, these steps are how I create a very specific look which I personally like and which I think lends itself to landscape and fine art production. Only Step 1 is specific to the SD Quattro so if you have a non-Sigma camera, then jump to Step 2.
Step 1: raw image conversion in Sigma Photo Pro
As stated already, I do not tweak the image at all at this stage, I rely on the in-camera setting of increased contrast, reduced sharpness and the colour mixer giving me 100% in the red channel. The purpose of this step is to retain those settings and convert the raw file into a 16bit TIFF for further processing.
Step 2: initial processing in Adobe Lightroom
The purpose of this step is to perform any obvious crop if I can see straight away that it would be beneficial, and to also perform any horizon correction if that is needed. At this stage I will also check the overall dynamic range of the image and I might make an exposure adjustment if necessary. If there are any hotspot issues I will take this opportunity to address them, either using a radial filter, an adjustment brush or both.
Step 3: layered adjustment in Adobe Photoshop
From Lightroom I choose the option to edit the image in Photoshop, retaining any adjustments made so far in Lightroom. In Photoshop, I copy the entire image to the clipboard and paste it back as a new layer. I therefore have two versions of the exact same image on top of each other. What follows is very subjective, all depends on the specific image and what I feel suits it. A lot of this stage is experimentation and seeing what looks good. But, the general approach I take is to apply some level of gaussian blur to the top-most layer and use a blend mode plus layer opacity setting that retains the original image while adding softness, body and depth. The image that I create at this stage will be darker and flatter than the image I will ultimately produce, and this requires one further step.
Step 4: final processing in Adobe Lightroom
Back in Lightroom my task is to add dynamic range to the image and to bring out the highlights. What makes infrared images magical for me are those unexpected highlights, grass and foliage that is so pure white that it is almost luminous – it is that luminosity that I am trying to encourage at this stage. The subtle blur that I introduced at stage 3 helps to enhance this luminosity effect while at the same time helping to eliminate noise and other unwanted artefacts. The process I follow in Lightroom to create this luminosity is again not a strict process and I will make adjustments very specific to the image I am editing, but in general I will reduce highlights to minimum and at the same time raise the ‘whites’ slider to compensate. I may even reduce the overall exposure of the image to allow me to push the whites even further. Finally, I lift shadows to bring detail back to the image that would otherwise be lost.
Here is an illustration of those four steps in action. However, purely for the sake of illustration I have also cropped the stage 1 image to make comparison easier in-print. You can clearly see in the first image a central hotspot which was very straightforward to eliminate.
So why shoot infrared?
The kind of subjects I love to shoot are landscapes but, given both my location in the centre of London and the kind of work that I do, I tend to shoot cityscapes instead. Both these subjects have a lot in common – cityscapes are man-made landscapes after all – and both types of subject rely heavily on the weather and natural lighting conditions for their success to create mood and impact.
There are many times that I set out to capture a particular subject, yet come away without nailing the shots that I want due to weather conditions. What I realise from shooting infrared over the years is that it is an ideal alternative approach to image capture when lighting conditions for traditional images are not good. For example, there is nothing worse for a cityscape or landscape than a dull grey sky. Yet, the soft overhead lighting of a grey sky can yield exceptionally good results in infrared.
So, for me, having a camera that can shoot infrared means that there are much more possibilities to achieve good results, no matter what the weather decides to throw at me. This might mean carrying a second camera, which is not ideal, and a second set of lenses which is even less ideal. However, with the Sigma SD Quattro I can have just one camera and just one lens system with me all the time.
Read Tim’s latest blog post to learn more about extending your creativity with the Sigma SD Quattro.
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