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February 21, 2008
[ PHOTOS IN THE FOREST ]
OUR FORESTS ARE LOVELY – at least the bits that are left after the wood chippers have had their way.
The straight grey trunks soaring above our heads; the ferns and bracken clustered around the trees; the moss and hanging bark; the occasional stream and waterfall – it is all a photographer’s dream. And also a photographer’s nightmare. The photos seldom do justice to what our eyes have seen, and there are several reasons for this.
Our eyes see everything in focus, from the closest bracken to the highest tree canopy. A camera, left to its own devices, cannot cope with this extreme depth of focus. But with the right lens – an extreme wide angle – and the right aperture – f16 or smaller – a camera can do a reasonable job of keeping the closest and the most distant objects in sharp focus.
A tripod is essential for the serious forest photographer. We use the slowest ISO speed to get the best quality image and we couple that with the smallest aperture and that means long, long exposure times. We also prefer overcast days for even lighting, so hand-holding is out of the question. And windy days are no good for this activity because the leaves will be blowing all over the place and will be blurred.
Digital sensors are very good at discriminating between various shades of green – in our experience digital beats film in this respect. But once again our eyes are even better and we can see subtle shades of green even through the surface reflection on a leaf. The camera just sees a bright highlight which looks horrible in the finished photo. A polarising filter will cut the surface reflections on leaves and water, or the highlights on wet rocks. Using a polariser increases the richness of the colours that are lost in the bright reflected light.
Polarising filters further diminish the light transmitted to the sensor, making exposures even longer, so a tripod is essential, but so is some form of shutter release that doesn’t involve touching, and therefore shaking, the camera. A remote cable or infra red release is best, but you can also use the self-timer to fire the shutter 10 seconds after you last touched the camera.
However – there is always a however – to reproduce the widest tonal range we need to do a little High Dynamic Range processing.
The dynamic range of the light on objects in the forest is immense, from the bright sky above to the darkest shadows around the bottoms of the trees. A photo correctly exposed to reveal detail in the shadows will be featureless in the highlights. We can overcome this problem by taking three or more exposures at 2EV intervals (use the camera’s auto exposure bracketing) and then using a program like Photomatix to merge them into a single picture that preserves detail at both ends of the tonal range. Photoshop CS2/3 also has an HDR merge function under the File/Automate menu. It produces a flat-looking image that then needs to be corrected in Photoshop editing.
We may be deficient in soaring, snow capped mountains and vast, placid alpine lakes, but there’s magic in the forest of a subtler kind. You have to go to some trouble to capture it.
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Posted by terry at February 21, 2008 04:22 AM
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