A discussion in my Canon user forum (POTN, photography on the net) led me to a fun experiment!
A double exposure means capturing two different images on one frame. It is straightforward with film using a manual film advance with no locking mechanism (and can be fun) and with cameras preventing this can be similated by using a long exposure and putting a dark cloth or cap over the lens while changing the scene.
With digital there is no way do an actual double exposure. You can, though, blend multiple images together in a program like Photoshop quite effectively, in fact with better than double-exposure results (no transparency in the subjects)
But the idea of the cloth/cap technique came up so I thought I'd have some fun and try, not the black cloth, but another trick: with long exposures, quick movement becomes effectively "erased" as the sensor collects more light. So, with say a 10 second exposure, a person could pass in and out of the scene and not show up in the final image -- pretty cool! I've actually seen it happen!
So, I grabbed a stack of DVDs and put them in two piles and took one and leaned it on the left hand pile, set up my camera with a left point auto-focusing on the leaning DVD, set up a shot of 13 seconds at a fairly narrow f/8 aperture to ensure that both "exposures" of the DVD would be in focus, and using a cable release triggered the shutter.
After about 5 seconds I quickly picked up the DVD and moved it across to the second pile, and left it there for the remaining 6 or so seconds.
The results? as you can see, I'm now haunted by DVD ghosts! That's of course the problem with film double exposures as well -- I don't know whether it's better or worse with the digital-- but it's kind of funny. You can read all the DVD titles behind the ghosts!
The neat thing, though, is that you really can not see any motion evidence at all! No hand ghost, no DVD motion blur.
It occured to me that if I was using a white background (no detail) I could actually preserve a lot of detail in these suckers!
