Tuesday, 4 January 2011

Guide to Winter Photography


Slight underexposure, giving cold feel.
Winter photography can be quite challenging. The presence of large expanses of snow or frost is liable to confuse the metering system. In order to photograph winter scenes effectively, it is important to understand how the metering systems in most cameras work. The camera meter only “sees” in black and white (with a few recent exceptions) and it tries to set the exposure midpoint to 18% grey, which for many circumstances works well. However, when there are large expanses of whites or highlights, the meter will try to compensate by reducing the exposure, as it is programmed to record the scene as 18% grey to prevent overexposure. The reverse is true if there are large areas of darks and blacks. This is the reason that many snow scenes result in blue or grey snow, because the meter hasn’t recognised that the scene should contain lots of highlight areas (known as a high key image). Sometimes, a blue tinge is desirable for artistic reasons, but it is easy for it to seem like a mistake, even when it isn’t. Also, snow isn’t uniformly white, as it is rarely level, so there will be areas that should be in shadow, plus the flakes won’t fall in the same plane, so there will be variable light reflection from the snowflakes.
The effects of sunlight in a scene.
So how can we photograph snow scenes that aren’t underexposed, if the meter keeps adjusting? There are two main methods. Personally, I always use manual exposure settings and deliberately over-expose, but I recognise that not everyone is comfortable with manual exposure, particularly when the light is constantly changing. The alternative is to use exposure compensation. The precise method of setting exposure compensation will vary on the brand and maybe also the model of camera, but the principles are the same regardless. Nikon cameras also show the exposure reading in the opposite direction to other camera manufacturers, so check which side of the gradient is positive exposure and which negative. On Canon cameras, “zero” is in the centre, with negative exposure to the left and positive to the right. In an average scene (i.e. where there is alot of 18% grey), the meter will be in the centre without any compensation when the exposure is correct, if the meter is to the left, then it signifies under-exposure and the right over-exposure. Of course, in a scene with alot of snow, the meter should be pushed to the right, but the camera will set the exposure lower to centre the meter, which isn’t what we want. This is where positive exposure compensation is required, so in the camera’s exposure compensation section in the menu, the compensation needs to be set to the right (in Canon cameras) to increase the exposure relative to what the meter reads. But how much compensation is needed? This is where experience comes in, as different scenes will require slightly different settings. Generally though, 1-2 stops of positive compensation is a good starting point. In my experience, most scenes require around one and two thirds compensation, unless there is direct sunlight. Are there any dangers to using exposure compensation? The short answer to this question is yes, but it isn’t straightforward. The main consideration is the risk of overexposure. While you don’t want snow or ice to appear grey, you also need to be careful not to push the exposure too high, otherwise you risk losing the detail, particularly when you have areas of snow in shadow. You want to be able to distinguish between those shadow areas and the brighter areas, but if you overexpose, you risk losing the differentiation. Also, snow has texture, just like any other surface. Being able to see this texture adds to the interest and lifts the photo from the ordinary to make it stand out more. Direct sunlight, while adding interesting light, makes exposure more difficult, as it increases the risk of blown highlights. In scenes where areas of snow are being lit by the sun, then it is important to expose for those areas to prevent the risk of overexposure. This may put some areas in deeper shadow than you would like, but photography is full of compromises and in most cases it is possible to correct this in processing, provided the difference in exposure isn’t too great. If the areas of light and shadow are more defined, it may also be possible to use graduated filters to decrease the differences in exposure, just like you would with bright skies, but be careful not to overdo it, as you want to be able to see that there is a difference between snow lit by the sun and shadow areas. Some of us don’t get the chance for winter photography as often as we would like, so it is important to take the opportunities when they arise, to avoid the frustration of taking an amazing photo, only to get home and find it is dull and grey and not how you imagined at all. The key is to be prepared and to experiment, so that you can react to a scene with experience, rather than hoping for the best. While slight adjustments are possible when shooting in RAW, the more you need to adjust in processing the worse the outcome. Subtle is always best and in my experience, HDR photography doesn’t work well when snow is present. While this guide is for snow and ice, it can also be used for other scenes with alot of bright areas, such as water or other reflective surfaces or white birds or other wildlife. The principles can also be used for dark scenes, reversing the exposure compensation as required. Beyond anything else though, enjoy the chance to photograph the snow and be careful getting to your chosen locale. It may be useful to have chosen locales set up ready for when the cold weather arrives, so that long distance travel isn’t necessary.