“Artful” Blurred Water

by

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

Along the Little Tennessee River

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.

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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

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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. ;-)

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If you aren’t familiar with making multiple exposure images, read

Multiple Exposures – Made Easy

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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4 Responses to ““Artful” Blurred Water”

  1. jits Says:

    Amazing tip Ed, thanks a ton !

  2. rmiskinis Says:

    Ed,
    As usual I enjoy your posts. This one left me wanting to see a side by side comparison.
    I did my part by looking up ergodic theory.
    Bob

    • Ed Knepley Says:

      Good point. I’ll do just that in a future post from Great Smoky Mountains NP in two weeks where it’s hard to make an image that doesn’t have water in it.

      In the mean time, will you be trying it to make your own side-by-side? ;-)

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