Creating movement: the wind in action

Something I mused about for my Processes of Nature series was capturing the motion of the wind in a meaningful manner. On one of my photo walks in Norway recently I was playing around with some ideas. Here I'm going to run through what I was doing and whether I think it's working.

The trick, I reckon, is to get the sense of movement by having some fixed reference in the shot. If everything looks blurry, it might just be camera shake (photog movement) rather than subject movement. So I'm looking for something that resembles the classic sports shot with the subject blurred against a sharp background (or vice versa).

I tried a few things this time, all hand-held as I didn't have a tripod with me:

- Single frame, slower shutters. Using my 17-55 IS, I can handhold pretty slow at 17mm, probably down around 1/4s.
- Couple of frames blended (not very successful here)
- Multiple frames blended in several ways, building on my "virtual ND filter" that I used in an earlier post.

Here are the results

Single frame at 1/8s

Several frames blended using Photomatix Pro

Several frames blended by hand in Photoshop (lots of opacity adjustments)

I think this is showing promise, especially the blends. I don't think the proper effect can be gained consistently with a single frame.

What things would I look for in future?
First up, a longer base shutter speed for blending - maybe around 1/2s. Short speeds are tending to mean too much, or too irregular, movement between exposures.
Second, I like the manual blended; I can control the effect each frame has on the blur. Good point to start is us the base image as one near the centre of the movement range, then progressively decrease the opacity as the movement gets further from that central point. Gives a more natural look. For auto blending I'd probably go with more frames (I used up to six here: 1 fill of the 20D's buffer).
Definitely a tripod, otherwise the fixed reference won't be.