From my experience, anything above four minutes will make the water in a fairly still body of lapping water (such as a swimming pool) look like glass. The more turbulent the water, the more of that delicate "misty" effect you will get on the water. It's definitely worth doing a few experiments to see how these effects can be controlled.
Slight typo? 1/125 sec. is 8 milliseconds. 32 times this is 256 milliseconds. Mathematically, it would take 500 exposures of 1/125 to make 4 seconds, without allowance for reciprocity failure. It would of course also be possible to make multiple exposures, some at 1/125, some at slower speeds.
Originally Posted by Lee L
The direction of the flow also is important. If it is flowing perpendicularly to the camera, 1/4 sec (or longer if that's the desired effect) will do the job. If it's moving directly toward the camera, you may need longer minimum exposures to get that flowing look. In the end, the look you like the best is the best. It takes some experimentation.
I would agree with Steve above. However, I would probably go as slow as 1 second. Anything more than that, and you start losing detail, and the water just becomes a blob.
Sorry, it was late and I made a mistake. The indicated exposure was 1/4 second, not 4 seconds. So Les did his math correctly and I should have been asleep in bed rather than at the keyboard. :) Thanks for the correction.
Originally Posted by David H. Bebbington
There are two other waterfall photos in Les' book. One used a single 4 second exposure and the other used 20 one second exposures for an indicated 20 second exposure.
I'll add my preference for 1/4s to 1s as my favourite range as it retains the look of water whilst giving the swirling effect. Longer exposures can make it look like milk, loosing much detail which I do not find as attractive. That of course is just a personal preference.
I generally stick with either 1/2 second or 1 second, depending on the conditions of the water. Like Robert, I try to avoid the "white blob" and keep the detail in the water.
Tripod+slowfilm+small aperature+ND filters
This waterfall was taken at 2 seconds. A large falls from a long distance. Might be too "silky" for some folks, not enough for others.
As with any "special effect", the image should not depend on it to carry it...but instead add to the over-all image (or one runs the risk of creating another example of a cliche).