Some time ago now I decided to do some experimenting with slow shutter speeds and neutral density filters. The results of the experiments made it to our Photography Gallery so I thought I'd write a little bit about the processes involved.
You've probably seen many photographs of scenes where streams or rivers appear blurred, but everything else is clear. This effect is quite tricky to achieve with an ordinary camera. It involves a very slow shutter speed and this will result in the image being very over exposed, even with the smallest aperture setting.
So, to compensate for the brightness we need to prevent so much light entering the lens. The way to do this is with a Neutral Density Filter. When I'm working on film productions I often like to see outside windows when shooting interior scenes. A sheet of ND stuck to the exterior of the window will allow the outside to be exposed as well as the darker interior. Needless to say I have plenty of ND Filter gel lying around.
I started layering up the ND over the lens until the image became exposed. It took surprisingly many layers to do this. Once I had established how many layers were needed I stuck them together in a cardboard frame and fastened it to the camera with an elastic band. I then headed for the beach.
As I was heading down the cliff towards a favourite beach at Lansallos I thought I'd try a few shots looking down directly onto the sea's surface. I was really expecting nothing more than a blurry mixture of colour where reflections and sparkles would normally be. However, something quite interesting happened.
Each of the sparkles, that you normally only see for a fraction of a second on the surface of moving water, had added itself to the shot throughout the duration of the exposure. As a result of their fleeting existence they all appear perfectly sharp against the blurred surroundings. An interesting double effect is that as a result of the ND filters, the sparkles are actually perfectly exposed - they-d normally be "blown out" due to their brightness.
So the final image shows hundreds of sparkles, each one captured at the moment of its materialization, and perfectly exposed, revealing the true shape of a sea-water sparkle. They tend to take the form of tiny rings. Quite an interesting discovery and a pleasing image.
100% Crop of the above image
 - Dartmoor.jpg)
 - Dartmoor.jpg)
