This is an interesting technique that I used in my latest photo, The Explosion. Simply, you zoom the lens as you take the photo, and you get some cool motion blur, no Photoshop required.
Now, there are some concerns that you wouldn’t face with your normal photo, where the focal length stays constant through the exposure. Namely, these are:
• You can’t do it on most compacts, because the zoom is locked while taking the photo, as it’s controlled electronically. Using the method on a DSLR, where you turn the barrel yourself to zoom the lens, is usually the only option.
• You can’t do it with a prime lens (non-zooming), such as my favorite, the Canon EF 1:1.4. There’s just no zooming to be had.
• You need a slow shutter speed. It has to be fairly dark out, or in daytime, you have to close down the aperture as far as it goes, and maybe use a filter to keep more light out.
• With a slow shutter speed, you need a tripod. Camera shake does not look good, even in a zooming photo.
• Don’t try this with film, unless you want to waste a whole lot of film. Getting the process just right will take dozens of shots, and you’ll need to see what progress you’re making immediately to have any idea how to improve. This is really a place where digital shines.
To cut down the light, I screwed on a polarizing filter for the photo above, on the Canon Rebel XTi with the kit lens. It will work just fine; any 58mm circular polarizer will do for the lens. It cuts down about 1.5 stops of light (like F5.6 to F9.5), and makes the sky dark blue, …
