Sunday, 19 December 2010

How to take successful pictures of snow

So it’s snowing. Whoopee-do. And don’t we just love to take photos of it? Indeed, the media even go so far as to encourage us not only to take them but to send them in. “Have you got any pictures of planes skidding off runways? E-mail them to ...”
But snow is actually quite difficult to photograph, unless you are either (a) lucky or (b) possessed of a bit of knowledge about how cameras work.
So many of our ‘snow’ pictures turn out like this:

Not exactly the scene that caught your eye, is it? The reason is, that is how your camera is built to see the world.
Cameras and I have a lot in common — we both see the world as ‘grey’. A camera, even a modern digital one, doesn’t have a brain, so it can’t see that in one part of its field of view, something is bright, whilst in another it is dark. Instead, the light meter — the thing that measures the amount of light coming into the camera — is set to average out these light and dark bits and, effectively, mix them together.
You know what happens when you keep washing your watercolour paintbrush in the same water? All those vibrant reds, blues, greens and yellows turn to a mushy blue-gray. That’s what your camera does. Popularly it is referred to as ‘18 percent grey’, though technically it is not quite that dark.
But the result is that when your camera ‘looks’ at a snow scene, it says to itself, “That ought to be grey, not bright white, because that’s the way the world is according to Kodak, Fuji, etc.”
Actually, this works the other way as well. If you tried to take a photo of, say, a minister in a cassock (goodness knows why you would, but stick with it), the camera would again say, “That ought to be grey, not black, because that’s the way the world is ...”
The result, however, is that snow scenes, brides’ dresses, white sheets — in fact anything brighter than ‘normal’ — will under expose. The pictures will appear too dark, despite the brightness of the subject. Meanwhile, coal cellars, black cats, thunder clouds, etc, will appear too light, even though you might have been struggling to get a picture at all!
How do you get round this?
This is where it is very counter-intuitive. Basically, you have to over-expose light things and under-expose dark things.
There are a number of ways of doing this. On film cameras with a built-in light meter, you could ‘fool’ it by adjusting the ASA (film-speed) setting, reducing it to over-expose, or increasing it to under-expose. On really old, manual, cameras you could just open up the aperture of the lens to over-expose and close it to under-expose.
Many modern cameras, however, allow you to adjust the exposure directly: + for over-exposing, – for under. The snow scene below was shot by setting the camera to +0.7. (The number represents the old ‘f-stop’, where an increase of 1 stop meant a decrease by half in the light reaching the film. The + sign here actually represents an increase in the exposure, ie a decrease in the f-stop, but don’t let that confuse you.)
Another method is to use ‘spot metering’. Point the camera at something that actually is grey, lock the exposure, and then come back to your snow scene, which should now look something like this:

There is no hard and fast rule about the right exposure. If the sun is shining on the snow, you’ll probably need to go to 1½ or even 2 stops over-exposure (+1 or +2 on a digital camera). Fortunately, digital photography allows you to check the results. In the old days, you just had to waste film by bracketing.
Just remember, if the situation is reversed and the subject is dark, you need to under-expose. (My ‘worst case scenario’ was a black bride in a white dress on a sunny day!)

In summary: over-expose snow scenes, under-expose coal cellars.
So good luck, and I hope this helps.
John Richardson
Anonymous users wishing to paste in the comments box need first to select 'preview', then close the preview box. When posting your comments please give a full name and location. Comments without this information may be deleted.

1 comment:

  1. Er, sounds like you ought to investigate HDR...

    John, Manchester