Cotton candy flowing water
may be a photo-cliche, but
it’s a popular technique never-the-less
There are two ways to do this
One well-known and obvious, but
The second may come as a surprise
Redbuds & Cotton Candy
I’m leading an informal workshop in the Great Smokies in two weeks. This is an example of the type of scene we hope to capture. The GSM park has as many streams as mountains and this post is a pre-workshop tutorial.
The above image was made using the technique used for 99.999% of the images of this type.
A long(ish) exposure
Prevents the water from being “frozen”
How long is long depends on the speed of the water
The faster the water the shorter the shutter speed can be and still give the desired effect
The long exposure can be achieved several ways –
Stopping down the aperture to the f/18-22 range
Using a neutral density filter (or in a pinch a circular polarizer might hold back enough light to suffice)
And, don’t overlook this one, set your ISO to the lowest value your camera offers
All of the above combined
But – there is another way
This technique is useful if –
Stopping down doesn’t give you the long shutter speed needed (maybe on a really bright day and/or slower moving water)
You don’t have a ND filter that helps get the job done
Never fear, Ed is here, with a trick that works –
Take 10 or so multiple exposures of the scene (using good multiple exposure technique which starts with a tripod – see link below)
These exposures, when combined into a single image (see link below for a Photoshop action that automatically combines the multiple exposures for you)
Will appear nearly identical to that achieved with a single long exposure
Put your camera on a tripod, set the release mode to continuous, and fire off a string of exposures; 10 is good
If you are interested the “why”, and are math/statistically inclined, look up the following for a justification/explanation of my claim (or just take my word and what your eyes see when you try it).
Ensemble averages (the multiple exposure in this case) versus
Time averages (the single long exposure in this case) and
When are they equal?
They are equal when the process is ergodic.
My assumption that the flowing stream is an ergodic process may be arguable (but I’ll stick to my guns based on the visual results).
So there you are – a photography and science lesson all in one. 😉
If you aren’t familiar with making multiple exposure images, read
which includes a link to a Photoshop action which automates the entire process of combining the exposures if you don’t own a camera that does it at capture.
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