Using Manual Exposure to Capture Waterfalls
Your camera is as dumb as a rock…so why are you letting it choose your exposure settings? You like photographs of silky flowing waterfalls but don’t know how to create them?
You’ll never get the effect you want when you let your camera choose your settings. With a little knowledge of how a camera works, you too can be creating the kind of photographs you hoped to take when you laid out all that money for your new camera.
Those automatic exposure settings simply won’t capture flowing waterfalls.
The first thing you should do is set your camera's ISO setting to 100. That will reduce the sensitivity of the sensor to its lowest level. You will be using long shutter speeds so you will want to minimize the amount of light captured by the camera. Low ISO settings and small apertures are essential.
Next, take a meter reading of your waterfall.
Let’s assume that your meter tells you to shoot at 1/30th of a second at f5.6. We know you are not going to get a silky waterfall at 1/30th of a second but we should get one at ½ second. Now, set your camera to manual mode and adjust the shutter speed setting to ½ second. Then set your camera on a tripod. You must use a tripod because hand holding a camera with the shutter open for a half second or more will introduce body shake and your photo will be blurry.
Once your camera is resting on your tripod, compose the shot but don’t press that shutter release yet. By changing the shutter speed from 1/30th of a second to ½ second, you are letting a lot more light hit your sensor. For each full stop on your shutter speed dial, you are doubling the amount of light that will strike the sensor. So the change from 1/30 to 1/15th of a second doubles the amount of light. From 1/15th to 1/8th of a second doubles it again. Cut the amount of light in half again at ¼ second and once more to ½ second. You have doubled the amount of light four times.
To get the proper exposure, you will need to reduce the amount of light entering the camera by an equal amount. The way to do that is to adjust the aperture so that the hole in the lens that the light is coming through is smaller. By adjusting the aperture from f5.6 to f8, the amount of light is cut in half. To get the correct exposure, you will have to reduce the amount of light in half four times, just as the increase in shutter speed doubled the amount of light four times. Setting the aperture from f8 to f11 cuts it in half again, f11 to f16 another half and from f16 to f22 for a total of four stops. So we will shoot our waterfall at ½ second at f22.
The same amount of light will hit the sensor at these settings as at the original camera selected setting.
Because you now have the same effective settings as the original meter reading, doesn't mean that you have the proper exposure. Keep in mind that your camera sees everything in shades of grey. It thinks snow is grey. It thinks coal is grey. So, you might have to make additional adjustments. If your photograph will include mostly fast moving water, you should allow more light into the camera either by leaving the shutter open longer or opening the aperture. One full stop should be sufficient.
Keep in mind when shooting waterfalls that you want to select a shutter speed of 1/2 second or slower if possible. You want your ISO setting to be 100. Once you've made those selections, you have to set your aperture at whatever setting it takes to get the correct exposure.
With these settings you can expect to capture the silky motion of the waterfall because you chose the settings, not that dumb as a rock camera.