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Hi njg39,
Blown highlights in photographs is something we all have to contend with no matter what make or model of camera we use. There are a number of methods you can employ to combat them, but first do you understand why the highlights are being blown out?
Well it all comes down to the camera's metering system, which basically analyses all the light values from the scene you're trying to photograph, from the shadows through to the highlights, but the range of values is too wide for it to control so it finds the average from all the values and records what it can from either side of the centre line. This means that it will clip both the shadows and highlights, ie those areas both above and below the sensors physical range.
One way to see this is more clearly is to use the histogram on your camera. The histogram displays all the different visible light frequencies as differing shades of grey, starting from 0 on the left-handside, which is absolute black, through to 255 on the extreme right-hand side, which is white. So to stop your camera from blowing the highlights you need to watch right-handside of the histogram and by adjusting either the aperture or shutterspeed or ISO to bring the vertical bars on the right-handside of it so they are just touching the far right-hand edge. Now this may mean that the rest of your image looks a bit under-exposed, but you can lighten the shadows using curves when you edit your shots with your photo-editing software to bring these back to where they should be.
Another method is to take two exposures and merge them together. With a landscape you will often find that the sky is sometimes 2 - 3 stops brighter than the land and the sky always gets blown out. So you take one shot metering on the sky and a second shot metering off the land and then merge them together. You will need to support your camera on a tripod and take two shots of exactly the same image so they will line up perfectly, because if the second shot is taken pointing at a different angle to the first you'll struggle to blend the images together.
The other answer is to use a filter to balance the sky with the land. The two most popular are an ND Graduated filter and a Circular Polariser. An ND Grad is usually a square filter that fits into a filter holder that clips to an adapter ring. Looking at the filter you will see that the top half of the filter has been darkened, like the lens in a pair of sunglasses, but it starts off very dark and it gets progressively lighter until after the middle where it is completely clear. This cuts down the amount of light entering the lens from the sky to balance it with the amount of light coming from the land. ND Grads come in a variety of different strengths depending on how many stops of light difference there is between the sky and land. They can normally be stacked if you need more than one filter to blance the sky and land light values. A Circular Polariser also cuts down the amount of light entering the lens by filtering out the polarised light that has reflected off a suface and is diluting the direct light. It can be adjusted, by twisting on half of the filter until the blue of the sky darkens and the clouds turn lighter. It works best when shooting at approximately 90 degrees to the sun. Its also used for removing reflections from non-metallic surfaces too.
Anyway, I hope that's given you some idea of what you need to do to stop the highlights from being blown out on your shots, but sometimes when you look at a scene you have to decide what detail in the highlights you don't mind blowing and what detail in the shadows you don't mind losing too.
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11-02-11, 09:19 PM
