You've probably seen photographs of waterfalls and cascades that have that nice, silky effect in the water, and perhaps you've wondered how this is done. Well, it's not as hard you might think. There are some simple things you can keep in mind that will allow you to achieve the same effect in your photographs.
You get the silky effect in the water by having a long shutters speed. When there's no wind, everything in your picture will be still but the water. So if you use a long shutter speed and a small enough aperture, the whole photograph will be sharp except the water. Since water flows consistently in its channel, the motion blur in the water will give it that flowing, silky effect. Here are some things to keep in mind:
1. Go early in the morning before the sun hits the scene. Direct sunlight will cause too much contrast in your scene, and your picture won't be as attractive. You will also have a difficult time getting a slow shutter speed.
2. Set Your Shutter Speed and Aperture. The proper shutter speed depends on the speed of the water, but I've found that a shutter speed of 2 to 3 seconds usually works just fine. Use your smallest ISO (I always use 100), and make sure you have chosen your aperture to give you enough depth of field. I prefer to shoot between f/8 and f/16 if that will give me the shutter speed I need. Take a shot and look at the results and adjust accordingly. You can use shutter priority mode and dial in the shutter speed you want, or you can use aperture priority mode and set the f/stop to give you the shutter speed you want.
3. Use a Tripod. Even with IS lenses, you will need a tripod to get sharp photos. If you have a cable or remote release, use it to trip the shutter.
5. Exposure Compensation. I've found many times that my camera will slightly over-expose waterfall scenes. I end up with "blinkies" in my preview screen in the brightest parts of the water. I frequently compensate by around -2/3 stop, but every scene is different. Check to see which works best for the scene you're shooting. You may find that the darker portions of the scene will look black in your photo, but this is better than having no detail in the waterfall, since that's your main point of interest. If like using HDR photography, take 3 to 5 photographs at different exposures to get detail thoughout the scene. I've done this with some success when I'm shooting prior to direct sunlight hitting the scene, but not after. And, I've found that if I'm shooting early enough in the morning, I can almost always get a photo just as good by playing with the middle exposure in Lightroom.
Above all, experiment and have fun. Try the above advice and vary it to suit your needs and tastes. And tell me how it went! For some ideas of how to shoot photographs, you can see my galleries for waterfalls on my smugmug site by clicking here.