ALTERNATIVE WAVELENGTH MANIPULATION IN DIGITAL PHOTOGRAPHY.
This is intended purely to be a quick-reference page and, not a scientific paper so for those with an even deeper understanding of the subject, please bear this in mind. On the same front, if you read anything erroneous or that could be expanded upon within the confines of the subject, please do drop me a line so that I can look further into it and publish on your behalf. For this, if I may have your patience, you have my profound thanks].
WHAT IS LIGHT?
We take light for granted. We see it everywhere; when it’s dark, we have a multitude of tools to create it. When it’s absent it’s missed and remarkable. When present – we barely remark on it save for the sight a beautiful sunrise or sunset, or perhaps the aurorae or, a light-show at an event, for example. What we see as light constitutes a very thin strand of electromagnetic radiation ranging from around 400nm – 700nm. (nm = nanometres or, x/1,000,000,000 M).
When looking at an object, what we interpret with our brain are lightwaves reflected away from that object which is reflecting light at wavelengths corresponding to its colour or colours. For example when observing an orange, it looks orange because it is predominantly reflecting electromagnetic radiation in a specific range or at a specific frequency of light (ranging from around 650-680nm or, the orange portion of the visible light spectrum: orange light). The same radiation of any colour has the same rules applied. Our eyes have cones which interpret light before sending these signals to our brains. We have different cones which each interpret light in three different and specific ranges of visible light wavelengths. When reflected light and colour seen by our eyes crosses these defined ranges of wavelengths, then the cones responsible for interpretation of these other wavelengths combine and send collective signals to the brain, thus creating the brain’s interpretation of a myriad of colours and shades.
© Pink Floyd
How do we get to see the colours of the visible spectrum? White light shone into a prism will slow down as it enters the prism and as it does so, will bend (this is known as defraction) and depending on the wavelength of the light, it will bend by a different amount hence we would see the component wavelengths of the visible strand of the electromagnetic spectrum broken down into separate component colours. The red end of the spectrum bends the least, violet, more-so. In the case of photography, the lens becomes the prism. But what are the colours and where do they come from?
THE ELECTROMAGNETIC SPECTRUM (EMS).
The Electromagnetic Spectrum consists of radiation from the Sun, ranging from very high frequency to very low frequency. (waves/sec or, hertz) – from gamma waves to radio waves. The part of the spectrum responsible for the creation of light, invisible and visible, ranges from ~0nm to ~1200nm.
The human eyes and brain can only see or perceive the strand of the EMS from around 400-700nm – this is known as visible light because it is the only range of the EMS that human beings can see – a very thin band of electromagnetic radiation within the entire spectrum. Each colour of the EMS corresponds to its specific wavelength. Remember learning ROYGBIV as a child? Well, that’s the visible portion of the EMS that we would see making up a rainbow. Or in the order of the visible light portion of the spectrum, from 400nm at the violet end to 700nm at the red end, VIBGYOR.
Thankfully, whilst our eyes are only able to see and interpret the visible light portion of the EMS, a camera may be modified either externally or internally, to ‘see’ ultraviolet and infrared light radiation, too. (Not all digital cameras are suitable for this but many are).
Ultraviolet light constitutes around 5% of the total sunlight on earth (compared with visible light: ~50% and infrared light: ~45%) and is divided into three components which we know as: UV-A, UV-B and UV-C. (Sources of UV light other than sunlight are fluorescents, tanning-machines, welding-arcs and LEDs).
- UVA: Range = ~315nm – ~400nm, some of which is absorbed into the atmosphere. UV-A is beneficial in producing Vitamin D.
- UVB: Range = ~280nm – ~315nm, around 90% of which is absorbed into the atmosphere. UV-B can be very harmful to skin, causing sunburn and potentially, skin cancer.
- UVC: Range = ~100nm – ~280nm, all of which is absorbed into the atmosphere. UV-C is extremely dangerous and thankfully, is absorbed by the ozone (O3) layer before it reaches the earth.
Normal glass as we see in windows is transparent to UV wavelengths from around 330nm or, UV-A light. The transparency is rather high therefore, almost all UV-A, visible light and infrared wavelengths will pass through glass – not all, but most. Because the transparency of glass contains these properties, light wavelengths below 330nm (in other words, UV-B and UV-C light) are blocked at a concentration of almost 100%. Remember that UV-C light is absorbed by the atmosphere, however, as only around 90% of UV-B is absorbed in this way, approximately 10% of the radiated UV-B light is still present. As normal glass blocks almost all light below 330nm, it is reasonable to assume that some UV-B light may pass through it, though the amount would be very small.
Infrared light radiation constitutes ~45% of the sun’s total emitted light. It is invisible to the human eye and ranges in wavelengths from ~720nm – 900nm (also known as near infrared) and, ~900nm – 1200nm (or, far infrared). Infrared light has longer wavelengths and lower frequencies than UV light.
Common subjects for IR photography are largely, landscapes where green foliage or plant materials are plentiful. In such scenes, amidst bright sunshine (high in IR radiation) the ‘Wood Effect’ is a clearly recognisable phenomenon. Here, ‘Wood’ does not allude to the material but the name of Robert W. Wood – a pioneer in the field of IR photography in the 19th Century who discovered the white photographic reproduction of leaves and foliage of deciduous plants being caused by strong infrared radiation from chlorophyll layers in their foliage. In reality, there can be many differing genres of photography suitable for IR consideration. The only way to see if your chosen subject will work for IR shooting is to try it and see what results you’re returned with. It is safe to say that for successful infrared images, good sunlight is essential since the sun is our only natural source of IR radiation or light. Man-made structures, wide angles and rural-scapes are often very successful subjects but portraits too can be extremely interesting.
(From a Full-Spectrum Conversion w/720nm R72 over Lens Element.)
TRUE FULL-SPECTRUM PHOTOGRAPHY [or – Luminous Tone Full Spectrum / LTFS].
Why is it referred to as FS and, what do we actually mean by this? To answer the second part of the question first, put simply, a camera shooting true FS has all of it’s factory-fitted blocking filters removed; that’s the UV and IR blocking filters to be more precise. Furthermore, the thin layer of glass which sits in front of the sensor is removed as is the anti-aliasing filter. What is left therefore, is the silicon sensor, completely naked, which is now able to record all light-waves within the EMS from UV-B at ~280nm (remember, ~90% of UV-B is absorbed into the atmosphere therefore UV-B pollution is small in comparison to the rest of the lightwaves hitting the sensor – but what’s left in our atmosphere is recorded) right through the visible spectrum all the way through to far infrared at ~1200nm. Given the ‘strengths’ of these light-waves within our atmosphere, it is understandable that as light is being recorded by the sensor, what is being recorded is:
- Dominant VIS light (~50%)
- Strong IR light (~45%)
- Very small % of UV light pollution. (~5%)
As a result, for colour images, results will look rather strange as compared to simply visible light, colour images that our brains are accustomed to processing through our eyes. Colours recorded will be a mixture of those recorded by all wavelengths from 280-1200nm; just like the cones in our eyes do, except that they only collectively process the VIS portion of the EMS. In true FS, there are however three times more divisible wavelength strands to process in total compared to what we see with our eyes and perceive with our brains, therefore,much more recordable light.
To answer the first part of my preamble – why true FS? I think in some way I have already answered this question in the previous paragraph but to be more specific, true FS doesn’t only afford one the ability to shoot false colour utilising the entire EMS – that’s not really it’s strength, but better still, it is absolutely wonderful for black and white photography. UV pollution affords more detail in shadows and dark areas of the frame, VIS gives us plenty of what our brains are used to in image sharpness, contrast and focus, while infrared light pollution lends a certain softness (IR wavelengths usually focus at slightly longer lengths than VIS light hence, IR focus scales on many old legacy lenses that you may have seen or used) and grain to the whole image. Put all of these light qualities and characteristics together from the different portions of the EMS and you’d be right to assume that images produced this way would most certainly not be for obligatory or habitual pixel-peepers, but for prints, and normal viewing, the results can be astounding. Colour images can be worked in software such as Lightroom for WB adjustment and colour correction, and black and white images the same, with an added benefit – much more recorded light.
(Colour FS under Various Light Sources / Handheld).
[Any M-Mono Shooters: Please Read before you Cuss!]
A few years ago, a very (the most) prestigious camera manufacturer introduced a camera called the Monochrome. You may have heard about it, read about it, drooled over images on the web and cursed the fact that it is and always will be just way too expensive (for most of us) and thus, utterly unattainable. In my view, the Monochrome is largely a pointless camera. Sorry, but there it is. Now I know I’m going to potentially offend Leica fans by having said this, as well as those reading who have saved for years or perhaps even re-mortgaged a property to fund one of these things, but before anyone writes in with a rant, please allow me to explain as comprehensibly as I’m able to, as to why the Monochrome is not actually a sound investment of money, or dribble either. No, I’m definitely not bashing Leica; I’d love to own one (even though I’m really not sure why)– this isn’t about Leica; it’s not even about the idea of a dedicated black and white only camera – it’s about the physics of the Monochrome.
Firstly, to get this out of the way, I have yet to see published a mono image from the M-Monochrome which makes me wish I had one. By this, I’m not slating it – I have just never seen anything special from one that wasn’t a result of the glass on the front of it. I use a few different cameras and all produce wonderful black and white images with the right exposure and (subjective) processing. None of my cameras are Leicas and neither are any of my lenses either. In my view, I don’t get how the Monochrome can be better at producing black and white images on the proviso that a monochrome picture is all that it can produce and, I certainly don’t see it. In my view, all cameras produce images and whether you prefer one look or another from any camera is your choice; again – it’s completely subjective. Still, I digress but it’s an important point. It’s important because there is a very significant tool available to any photographer who wishes to produce more tonal black and white photographs. This tool is called – colour.
How beautifully (and, conveniently) ironic.
Without breaking down the anatomy of the Monochrome’s sensor array (though by it’s given model-name I would imagine it to be obvious) there is no colour array therefore what it records with each trip of the shutter are not colours which are then converted to black and white in-camera (as with cameras set to JPG (Mono) +/- RAW), but directly interpreted shades of grey from the light and exposure information it receives upon metering and subsequent shutter-activation. Without argument, the non-existence of a Bayer (colour) filter does afford an extra stop or so of light to reach the sensor and this may well assist the Monochrome’s very well regarded high ISO capabilities. Furthermore, because there is no colour information to be processed, the need to adjust WB accurately is removed thus not requiring such amplified signals which would also exacerbate image-noise and / or loss of detail. These factors I believe to be crucial to the Leica’s individuality and appeal to mono-shooters. But I don’t shoot at ISO 8000 and will probably never need to. The presence of image noise for the sake of colour manipulation for black and white output is a trade-off. If the noise produced happens to be of a more filmic character (this will depend on your camera and more-so, its sensor specifications, construction and output) and less digital or uniform in appearance, then the chances of your final image being enhanced will be greater. But it all depends on what kind of output or look you wish to achieve. As an aside, I have images which when screen-viewing have displayed plenty of noise and yet when printed at 18” and viewed from as little as 3′ away show little to none and certainly not to the point where ever felt that IQ was affected. Quite the reverse, as it happens. But it must be accepted that many people don’t like any noise whatsoever. Personally, I think it’s unavoidable and part of the whole deal. Just like it was when I used my favourite Ilford ISO400 and 800 films.
Going back to the idea behind true FS for monochrome output, what are the benefits of shooting for black and white this way? At the start of this section I discussed the potential percentages of wavelengths which enter the sensor, which we now know is totally, completely starkers. Because it has no UV/IR blocking filters (which the M-Monochrome has retained, possibly because without them, older Leica lenses may not produce sharp images as the older lenses have properties of focusing on non-visible light at a different distance to VIS light), no AA or glass filters in front of it whatsoever, it is probably safe to say that the sensor gains an extra stop or two of light for this reason alone and, because we have more light (under sunlit conditions) from the invisible strands of the spectrum also reaching the sensor, it is safe to assume that ISO film-speeds can be kept lower and shutter-speeds higher. It is worth reminding ourselves at this point that even the omission of a protective glass filter in front of the sensor has the benefit of allowing extra UV light in, given that mostly, glass filters are inserted during so-called ‘Full Spectrum’ camera-conversions and of ~350nm (blocking all wavelengths below 350nm) and we know that there is recordable UV-B light from as low as ~280nm. Such full-spectrum converted cameras where this 350nm glass is inserted in front of the image-sensor, cannot truly be regarded as full-spectrum; rather they are actually split-spectrum. Think about it. If some recordable light is being blocked from entering the sensor, then the word full cannot apply or, even be an accurate representation of how much of the available light (visible and invisible) is able to be recorded. To further illustrate this point, imagine you are ordering a pint of your favourite ale at your local watering-hole and you’re presented with a glass that looks like it’s full, the bar-attendant perceives it as full (either due to ignorance, common misinterpretation, unchallenged previous like-practices by all of those who hate to make a fuss and, so on), and to all intents and purposes, it is kind of full. But kind of isn’t absolute. There sits on top of your beer almost an inch and a half of creamy, frothy head – which is void of the good stuff that you asked for. Is it a full glass? No. Therefore, you politely ask for a top up – after all, you’ve paid for it.
“May I have my missing 120nm, please?”
(FS Night-Shot | 15s @ ISO 100).
Shooting and processing images from a true FS converted camera can be a joy or a pain in the proverbial. It’s not all hearts and flowers because the unpredictability of the quality of light recorded can mean that your beautifully framed and taken image may well look less appealing than you might have hoped for by the time you upload your RAWs into your favourite editing suite. I find that it can be simply the luck of the draw on occasion and this too, is just part of the deal. Not every FS creation is going to whoo you. But then, what percentage of your normally taken shots do that anyway? Be honest.. we’re judged on what we show, not what we throw. But we throw.. and that’s the truth. However, when the light is just right and the capture likewise, when everything has come together, the composition, the colours, the shades, the correct exposure, the depth, FS will make you sit back in your chair and utter your favourite expletive.. probably twice.
Colour FS images are very possible and, whilst a little odd to get your head around sometimes, with careful processing it is possible for your brain to naturally, almost organically adjust your perception of what you’re looking at to the point of experiencing something of real beauty and almost other-worldly. When it hits you, you’ll just know it. Like faux-colour (false colour) IR imagery, colour FS can look astounding and extremely unique but how about black and white?
(Black & White processed from Image 4 (above) RAW / Colour FS Frame).
This is where FS comes into it’s own. Because all of the colour channels are recorded, when processing for black and white output or print, we still have all of the colour-channels to work with which gives us the most control over the monochromatic intensity and implication of each colour band. With these adjustments, additions of highlight, shadow, black adjustments are also possible (depending on your software) to taste and constitutes a fairly comprehensive array of tools workable towards the final image. Without the colour information, there are potentially seven fewer individual channels with which to use to create the finalised image. I for one would rather have the colour data and take a little extra noise, than a clean, noise-free RAW file with much less image data inside it. The fact that UV pollution gives a certain grain and added detail to shadow areas as IR radiation lends softness of texture and luminosity via the upper wavelength regions means that mono images shot using true FS conditions have a unique, balanced (though slightly less contrasty) and luminous appearance. Of course any look can be manipulated in software nowadays but I am a firm believer of getting a shot as right as possible in-camera before processing. Especially for shadow detail, FS works. If shadows are burnt out, there’s little to be done to recover detail. As I learn more and experience the difficulties I have had while shooting FS, under good sunlight, I make it a rule of thumb to under-expose by ~0.7 to counter the light I can’t see. This serves me well and often prevents blown highs. Of course, FS can be used in all lights for monochrome work, whether UV or IR is present or not. If theses wavelengths are not being emitted (for example, indoors, evening, low-light situations, to name a few) then they wont be recorded. For the major benefits of FS to be apparent it is solid reasoning to assume that all wavelengths which it is able to record must be present – only then is FS’s true and maximum potential achieved. Even so, without UV or IR radiation, one is left with camera which can be used for more or less normal black and white photography.
Without UV and IR light present as in the above examples, one can even shoot FS in colour and find that WB and colour trimming is not so difficult and actually can have a very pleasing, more normal output. Of course, by placing a UV/IR Cut filter over the lens, you have a normal camera recording VIS light only, or, if IR is your poison, place any IR filter over the lens instead, block all light wavelengths below that filter’s rating and use your camera as normal. Similarly, place VIS and IR blocking filters over your lens and you’re free to shoot in UV to your heart’s content. If you only wish to block VIS light, avail yourself with a UG-11 filter and shoot UV and IR combined. You have the entire light-spectrum to explore. Basically, choose your wavelength(s) and run with them.
(Faux-Colour IR | 720nm R72 on a Split-Spectrum Conversion).
SPLIT-SPECTRUM (ALSO KNOWN AS WHOLE-RANGE VIS/IR) PHOTOGRAPHY.
Split Spectrum is not that different from Full Spectrum (in theory and, in practice) and the major difference is made by the choice and strength of clear glass replaced in front of the image sensor. Typically this would render a difference of the lower 70-120nm or thereabouts. By blocking UV wavelengths up to ~400nm, with or without a clear glass filter in front of the sensor, one is left with visible light and near & far infrared wavelengths available, hence, split-spectrum recording. One can also refer to it as multi-spectrum, or, whole-range visible & infrared, however I prefer to refer to it as split and keep it simple. After such a conversion one is able to achieve almost as much and use the same techniques as when using a FS conversion – not only black and white photography but also colour photography (by threading an IR blocking filter onto the front of the lens) and IR photography, by threading on an IR filter of any chosen wavelength (for example: 590nm, 695nm, 720nm, 830nm) depending upon the look that you’re going for. It should be understood that (as an example) threading an IR filter such as an R72 (720nm) does not block all wavelengths other than 720nm, but all wavelengths below the value of 720nm. All wavelengths from 720nm and upwards will pass through to the sensor. Therefore, the choice or rating of the glass you choose for IR photography will determine the lowest wavelength at which light may pass through it to the sensor.
To be perfectly honest though, 99% of those who shoot with a FS or SS converted camera, will be using that conversion as a base, a platform from which to shoot IR by using their chosen infrared filters. Few will actually shoot in FS. But for black and white – there is a definite bonus in doing so, if only to see the real difference in tone and feel.
Using the same principles as already discussed, it is also possible to block UV and VIS light in order to capture mainly or, solely infrared light with our cameras. There are a number of ways in which this can be achieved which I will outline here, with some pros and cons to each method:
- Placing an IR filter of choice onto the front of a lens mounted to an unconverted camera.
- Pros: Quick, easy and cheap to do for any wavelength of choice by simply purchasing screw-on lens filters.
- Cons: Many cameras have an IR-blocking filter which would still need to be removed to succeed. Some lenses may not be suitable for channelling IR light, apparent by the display of visible to strong, sizeable light or ‘hot’ spots, in the centre of the image frame becoming stronger as the lens is stopped-down.
- Removal of the internal IR-blocking filter from the front of the camera sensor, thus allowing VIS and IR light to pass to the sensor and, use of an IR filter of choice over the lens’ front element.
- Pros: Permits SS photography without the use of any external filters. Quick, easy and cheap to do for any wavelength of choice, though limited to wavelengths upwards from ~400nm, by simply purchasing screw-on lens filters.
- Cons: Internal conversions can be expensive. Some lenses may not be suitable for channelling IR light, apparent by the display of visible to strong, sizeable light or ‘hot’ spots, in the centre of the image frame becoming stronger as the lens is stopped-down.
- Removal of internal IR blocking filter and replacing with an IR filter of choice, internally, blocking all wavelengths below the rating of the inserted filter.
- Pros: Makes for a dedicated IR only camera. No need for external filters on the lens. Higher rated filters can be placed on the lens if longer wavelength IR images are sought.
- Cons: Careful choice of internal IR filter is required, as, too high a rating will limit the user to longer wavelengths only. Conversely, a lower rating of IR filter will still allow longer wavelengths to be captured. For example, a 590nm ‘Goldie’ filter will permit all light from 590nm upwards into the IR spectrum to be recorded by the sensor. By placing an 850nm IR filter onto the front of the lens will permit light from 850nm and upwards, only, useful for darker skies in the right conditions and, higher contrast monochromatic IR images. Overall, a versatile choice to have. Internal conversions can be expensive. Some lenses may not be suitable for channelling IR light, apparent by the display of visible to strong, sizeable light or ‘hot’ spots, in the centre of the image frame becoming stronger as the lens is stopped-down.
- Internal conversion to FS by removal of all internal filters anterior to the sensor and use of mounted IR filters over the lens element.
- Pros: The most versatile option as this allows shooting any range of wavelengths within the EMS or simply black and white FS. Once converted, quick, easy and cheap to do for any wavelength of choice UV/VIS/IR by simply purchasing screw-on lens filters to block / permit your chosen wavelengths.
- Cons: Internal conversions can be expensive. Some lenses may not be suitable for channelling IR light, apparent by the display of visible to strong, sizeable light or ‘hot’ spots, in the centre of the image frame becoming stronger as the lens is stopped-down.
- Infrared processing profiles in some editing suites. (It’s an ‘option’, so I have to mention it).
- Pros: No need to purchase any IR or FS conversions, filters, or learn anything about the subject or, shooting in alternative wavelengths.
- Cons: Do I really need to list them? (It’s real, or, it’s fakery.)
THE IR ‘LOOK’.
Having already alluded to the Wood effect, no doubt you will accept that the real draw to IR imagery is the way that some scenes look when photographed amidst strong infrared radiation or, light. I posted a series of images on Flickr many years ago, taken of a fly-fisherman. It was a mid-summer waterscape surrounded by pine forests, below a gorgeous blue sky and was photographed using an old Nikon D70 which I had had converted internally to 720nm IR. A few hours after posting that faux-colour IR image received a comment. “I love winter!” it said. I chuckled a little but looked again at the photograph and besides the presence of the aforementioned fisherman, one could have been forgiven for thinking that this may have indeed depicted a winter scene. IR photography performed in the right conditions does yield spectacular and unique, pleasing and exciting results. There’s a definite draw towards capturing light that we cannot see, especially when it can look so beautiful and so different. It’s almost a naughty pleasure. Just remember to set your WB correctly before you start shooting (usually using sunlit grass to measure off or, a vibrant green card under daylight can work almost as well. These are usually available cheaply from most stationers or craft-shops).
Lets quickly talk about filter choices and the looks they can provide. It’s really very simple yet largely, your own tastes, experiences and processing ideas, proficiency and techniques will have just as strong an influence on your final image as the light with which you chose to shoot, I assure you. If you shoot in RAW then your latitude for processing will be much wider than working with compressed JPG files. [This is not a comprehensive list of available filters or wavelengths, just a mentioned few to give you an idea of benchmarks as in, different looks that you might achieve].
- 590nm: The Goldie look. Lets in plenty of the upper ranges of VIS light as well as IR. Great for more vibrant output with a strong IR overtone.
- 720nm: Arguably, the accepted Universal Standard for IR photography. Superb for mono-IR, nice contrast and for deeper skies and, can also be utilised for faux-colour output (by swapping the red and blue channels in post-production). Personally, I find that faux-colour processing is: a) a pain. b) seldom looks all that pleasing unless my WB reading happens to be absobloodylutely bang-on.
- 830nm: For mono only. No real perceivable colour gets through this one. Wonderful for richness, grit, contrast and pure impact. You’ll need strong sunlight too. With an 8-stop ND for example, possible to capture cloud movement in dark skies with your chosen foreground bathed in lovely IR light. Wider angles would be useful here. Think imposing ruins, disappearing stone-walls or dykes, magnificent trees, knackered or rusty old machinery – you get the idea?
- 950nm: [Upwards] – for the die-hard, deep, deep contrasty scene-seeking photographer. As with the 830nm but longer exposures required because you’re getting in far-infrared now.
It’s time for me to ask for your forgiveness; this page has pushed on a bit, and, if you’ve stuck with me this far then, thank you, I hope I’ve been able to shed some proverbial on the subject matter discussed and, bloody well-done to you, (because I believe that there’s only so much online reading anyone can stand in one stint). I love alternative wavelength photography and, I have a deep love for IR, it’s complexities, it’s rewards, it’s unpredictability and surprises. I couldn’t have written any of this without it. That said, I hope you find what you love, look after it and enjoy it to the maximum. It truly can be the stuff of dreams.
Please, do get in touch if there’s anything here, or out there, that you’d like to discuss. Hopefully, this will have all made some kind of sense and if you have any queries, corrections or points to share, please do drop me a line via the comments section.
[Further reading for the utterly devoted – Mangold et al (European Journal of Physics) 2013 – The Physics of NIR Photography. NIR Photography – Mangold et al – EJP2013 ]
This page is written with humble, unending and deepest gratitude to my friend, without whom little of my alternative-wavelength equipment and most of my understanding would simply not exist. To The Doctor – thank you! A true genius and the very truest of friends.