One Exposure is Not Enough
Those who follow me on Google+ will be very well aware that I've recently started testing a technique known as "Multiple Exposures" - new to me, not to the world of photography, of course.
It's actually pretty simple and has been used for a very long time. Back in the analog film days, the photographer simply exposed the same sheet of film multiple times by not winding the film to the next frame.
In today's modern digital cameras, you often have a special feature called "Multiple Exposure" in which you can define the number of exposures to blend and the method to do so.
On my Canon EOS 5D Mark III I generally use either "Additive" or "Average" mode.
I usually choose additive mode, in low light situations as you can shoot with much shorter shutter speeds than in Average mode or for regular single exposures.
Additive is doing the exact same thing as you would do with an analog camera, it adds the exposure values of each individual frame which means you will have to underexpose your shots depending how many you're shooting.
Here is an example:
1 Exposure = 0 EV
2 Exposures = -1 EV
4 Exposures = -2 EV
8 Exposures = -3 EV
... and so on.
Can you see the pattern? It's actually really simple. Forget about the number of exposures for a minute and simply think in exposure time. When my camera meter suggests a shutter speed of 1/10th with an aperture of f/7.1 and ISO 100 to get a proper exposure and I shoot 2 exposures, I need to shoot each individual one at 1/20th to get a total exposure time of 1/10th. Got it?
So with 8 exposures, I had to shoot each frame at 1/80th of a second. Adding to those 8 frame together brings me back to a total exposure time of 1/10th.
In order to get the desired effect, I focused on the center of the crane and placed it right into the middle, exactly where my center focus point is, I then turned the camera slightly clockwise until I completed all 8 frames.
The great thing about the 5D Mark III is that you see the resulting image after every shot so in case you didn't underexpose enough, you can stop shooting after 6 or 7 to prevent an overexposed image. If you would be shooting in live-view mode, you can actually see the a ghost image version of the previous ones while composing the shot, this works much better in average mode but more to that later.
I'm shooting Average mode during the day when there is plenty of light. For this particular photograph, I focused on the tree and aligned it as equally as possible for each frame while walking around it, trying to keep the same distance. You will not get it perfectly aligned but that's exactly what makes those photographs interesting.
I shot all 8 exposures with the exact same setting:
1/400th at f/8 and ISO 100