Thursday, October 7, 2010

Photography Tutorial : The Light

Photography needs light – and not just any light. You are unlikely to shoot outstanding pictures if the light is wrong. How do you get the right light when there is little you can do to control the sun?

The answer is simple. You can improve your pictures by shooting at a different time of the day, or even a different time of the year.

The quality of light 

The quality of light changes throughout the day. Early morning and late afternoon sunlight has a warm colour, whereas bright sunlight in the middle of the day is much bluer. Why is this?

Scattering of the sunlight causes the change. Dust and water particles in the atmosphere reflect, refract and absorb the various wavelengths of light by differing amounts. At noon, the sun is overhead and the light travels straight down through the atmosphere. Very little scattering occurs and the sunlight is blue-white.

In the morning and evening, the sun appears low in the sky and the light has more atmosphere to travel through. The short (blue) wavelengths of light are scattered more than the longer (red) wavelengths, leading to a warmer light. As a general rule,warm light provides more attractive images, especially for landscapes and buildings. If you are visiting places on holiday, the ideal time to capture images is in the early morning, soon after sunrise. Not only will the light be right, but there will be fewer people around.

Another advantage of shooting early or late in the day is the low angle of the sun to the ground. This throws long shadows, which add to the interest of many scenes.

Of course, sometimes the angle of the sun means that your whole subject is in shadow, which is not ideal. Fortunately, the position of the sun moves during the day. It rises in the east (or thereabouts) and sets in the west (or thereabouts). So if you have the time, you can stay in one place all day and wait for that special moment when everything is perfect.

Of course, if you are travelling and passing through a place, it might not be possible to return when the conditions are better suited to photography.

Shooting the sky

The image we capture with a camera is frequently not quite the scene we see in front of us. Dynamic range is used to describe the difference in the levels of brightness from light to dark in a scene. On a cloudy day, the dynamic range is low whilst on a sunny day, the dynamic range is high.

If you look at the landscape photographs you have taken on your existing camera they may have a pale sky, even though it looked blue at the time you took the picture. The camera has exposed to give detail in the darker tones on the ground, overexposing the bright tones of the sky.

Digital camera sensors do not have the same dynamic range as the human eye. Many current PowerShot and IXUS models have Intelligent Contrast Correction technology (i-Contrast) which automatically expands the dynamic range.

If your camera doesn’t feature i-Contrast you could use the Exposure Compensation to give correct exposure for the sky, but this would underexpose the ground.

Fortunately, there are several solutions to this problem. One solution was described earlier. Wait. But if you are impatient for the picture, there are photographic techniques you can employ.

If you own an EOS Digital SLR then there are a number of solutions involving filters that will allow you more control of the sky’s appearance in your images. Some PowerShot models also accept an adapter that allows filters.
A graduated filter is one answer. This is a filter with a toned area at one end, but clear at the other. If you attach the filter to your camera lens so that the toned area is at the top, the brightness of the light from the sky will be reduced as it passes through. This will reduce the dynamic range of the scene, avoiding overexposure of the sky.

Most graduate filters are rectangular and slide into a holder attached to the front of the lens. This allows you to move the filter up or down to position the clear area over the ground while the toned area covers the sky.
Grey graduate filters have little or no effect on the colours in the image. The tone is neutral. However, you can also buy coloured graduate filters. These are still clear at one end, but have a tinted tone at the other including blue to improve a grey sky and orange to create a sunset effect.

Polarising filters can be used to darken polarised light. This is exactly the type of light you get from the sky – but only on sunny days, and only from those areas of the sky at 90 degrees to the sun. So if the sun is overhead, a polarising filter is useful when the camera is pointed at the horizon in any direction. But if the sun is low in the east or west, the filter is only effective when the camera is pointed north or south.

To see the effect of a polarising filter, simply attach it to your lens and rotate it. At one angle the filter has no effect on the light, but as you turn it polarised light will be partially blocked and you will see part of the image darken. So not only can you reduce the brightness of some skies, but you can also control the level of brightness. Clouds are unaffected by the polarising filter, so they stand out clearly from a darkened sky.

There is one method of dealing with overexposed skies that has been around since the early days of photography. This involves replacing the sky with one you shot earlier.

Some photographers build up a bank of sky images for this purpose. It is easy to do. Whenever you see an interesting sky, take a picture exposing for the sky. You will soon have a number of images showing attractive cloud formations.

You can then merge a suitable sky shot into an image with a plain or overexposed sky. This was a darkroom technique practiced by many film photographers. Today it is a computer technique that involves cutting and pasting one image into the other. It takes a little practice, but you work on copies of the digital images so that you can keep starting again until you get the result you want.

So whether you wait for the right light, adjust your image with a filter or add another sky of your choice, photographs of sunlit sky offer a wide range of opportunities. Now go out there and get shooting!

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