Wave-particle duality

Now you know what is the best camera to use to take compelling award-winning images, you might also need to know a wee bit about another essential component of photography.


(All you grizzled old pros out there know all this stuff already so you can skip this post!)

Light is simple stuff really, but fundamentally weird at the same time. How weird? Er…um…well, very weird.  Light bends, bounces and blends, changing its appearance and often the appearance of the things it hits in the process, as it goes about its business; and that’s just the simple stuff.

Wave-particle duality is one of it’s more peculiar and complicated aspects, albeit happening at a very very small scale. This is the ability of a photon – an ‘elementary particle of light’ – to travel as a wave (and thus apparently ‘appear’ in two places at once) yet arrive at its destination as a single particle. If that’s something you find intriguing I can recommend John Gribbin’s wonderfully informative book ‘Schrodinger’s Kittens and the Search for Reality’ which may (or may not) go some way towards explaining some of the underlying strangeness of light. Any book written by a scientist that uses exclamation marks as often as Gribbin does is a winner in my opinion! I’ve read it, and some bits of it more than once, and I am still struggling to get my head around whats going on ‘down there’ at the small scale where much of this weirdness occurs. Thankfully that puts me in the company of almost 99.9% of the general public, and probably a high proportion of scientists too.

But you don’t need that degree of interest, and to read a book, or even understand very much of what you read, to become aware of how magical light is, and what it can contribute to your images. You can just use your own eyes, see it’s magic at work every day.

The old saying “F8 and be there” is very apt, but the response that no-one EVER makes is: “Ok F8 it is, and I’ll be there for sure. But what time should I be there, and where is ‘there’ , I mean………where should I be?”

So what difference does the time make? And why would one’s location make any difference?

Have a look at this image below. What are you looking at? Why is there such a contrast in colour? And where are the those colours coming from?

Isle of Mull © John MacPherson


Some basics to help you along as you mull it over (assuming outdoors light, not artificial): the lighting in a scene can be cool or warm (commonly referred to as its ‘colour temperature‘).

To put it simply ‘white’ light is made up of a range of colours, different wavelengths of light, all of which combine to make up the visible spectrum. Remember the school experiments with the prism and light? ‘White’ light goes in one side and a rainbow explosion comes out the other? That’s the stuff I’m on about. Basically, out in the real world the different wavelengths of light, from short to long, violet at the cool end through indigo, blue, green, yellow, orange to red at the warm end, are affected to varying degrees by the things they interact with on their way to your eyes. The main thing they pass through is the earth’s atmosphere. When the sun is low on the horizon, at sunrise or sunset, there is more atmosphere for the light to travel through and this means that more light is scattered and absorbed, particularly the short wavelength blues and greens, leaving only the longer red wavelengths to reach you, thus you perceive a dimmer but redder sun.

At noon the sun is directly overhead, with less atmosphere to absorb its rays, so we see a brighter but ‘cooler’ light. The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths red, orange and yellow pass straight through unaffected by the air. However, much of the shorter wavelength blue light is absorbed by gas molecules, then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue and provides a cooler bluer ‘colour temperature’.

To add to this heady mix, when a scene is in shade on a clear day, because there is no direct sunlight, the main source of illumination is only the blue sky, and so the shadows will have a cool blue colour cast. Your eyes will not generally detect this as your brain adjusts to compensate, to make what you see appear ‘normal’. Digital cameras must consider this though, and all of them have an AWB (Auto White Balance) control mechanism which also tries to adjust the overall colour of your image so that it appears ‘normal’. Film however, which is what the images included here were captured on (Fuji Velvia), does not have AWB and therefore reproduces the varying colour casts more ‘accurately’, letting you more easily see the colour shifts.

So, to capture the scene above I stood in the shadows, on a cloudless sub-zero winter day. Because I’m in the shadows and photographing a scene thats also in the shadows, the overall colour is cool blue from the clear sky overhead. But the ‘trick’ is that not all of the water surface is reflecting the same thing, some parts of the water surface, the little waves, are reflecting that clear blue sky overhead, thus appearing blue. However on the opposite side of the bay facing me there is a huge swathe of golden bracken, lit by the low winter sun, and this is also being reflected, but only in the flat surface of the water that is at the correct angle relative to the sunlit hill and me, thus appearing orange. The consequence of this is that one wave face reflects blue, and the other flatter surface reflects orange. Water is a good reflector and can easily produce these interesting effects, but any light-coloured surface, sand or snow for example, will also reflect any particular colour cast that exists in a scene. I could only capture this effect by standing in this specific location relative to the sunlit hill and blue sky. The ‘F8 and be there’ in this instance meant precisely ‘here’, in this spot, at this time of day.

Consider the picture below. You can see the golden bracken, and the distinct boundary on the beach where the white sand is reflecting the cool blue colour cast from the blue sky overhead, and beside it the directly sunlit area that appears ‘properly’ white.

Knowing something, even if only a little, about the ways that light can reflect, scatter, bend, carry ‘colour’, or even ‘soften’ or make more ‘harsh’ the scene or subject you want to record, can help to give your photographs an extra dimension. It’s also really good fun to try to work out what’s going on with the light in any scene, and at different times of day, testing yourself and your ability to observe and maybe capture a specific effect, or even just to sit and contemplate the wonder of it when you don’t have a camera to hand.

Isle of Mull © John MacPherson

Wave-particle duality?   Aye, nice to know about I’m sure, but at the end of the day most folks would probably prefer the sight of all the particles of seawater that make up those golden waves lapping onto a gloriously sunlit Scottish beach, with a loved one to share the experience.

Thats the joy of science, and the beauty of light, we’re part of its magic more often than we realise.


  • Ed

    More science and light and photography please!

    • Certainly sir. Will try sir. Must try harder, must try harder….!

  • I haven’t read it myself, but those of my acquaintance who have recommend ‘The Dancing Wu Li Masters’ by Gary Zukav – that’s if particle physics is your thing;-).

    • Thanks Tony – I’ll put it on the list. The reviews of it are very mixed, and it might just confuse me even more. Perhaps I’ll just go off and have a wee walk along the beach and clear my head instead………….

  • I think Hockney went on about this book a bit during his “joiner” phase.

John MacPherson was born and lives in the Scottish Highlands. He trained as a welder in the Glasgow shipyards, before completing an apprenticeship as a carpenter, and then qualified as a Social Worker in Disability Services. Along the way he has cooked on canal barges, trained as an Alpine Ski Leader & worked as an Instructor for Skiers with disabilities, been a canoe instructor, and tutor of night classes in carpentry, stained glass design and manufacture, and archery. He has travelled extensively on various continents, undertaking solo trips by bicycle, or motorcycle. He has had narrow escapes from an ambush by terrorists, been hit by lightning, caught in an erupting volcano, trapped in a mobile home by a tornado, kidnapped by a dog's hairdresser, rammed by a basking shark and was once bitten by a wild otter. He has combined all this with professional photography, which he has practised for over 35 years. He teaches photography and acts as a photography guide & tutor in the UK and abroad. His biggest challenge is keeping his 27 year old Land Rover 110 on the road. He loves telling and hearing stories.

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