Friday, April 13, 2007

Use your flash as a virtual shutter.

The Price of Pollen 6-2
Originally uploaded by Dalantech.
The shot in this post was taken hand held, but that's kinda deceptive. I took the image at F11 and ISO 100 plus I lost a full stop with a 1.4 teleconverter, and a little more light with a 25mm extension tube, so if the flash didn’t fire then the scene would have been completely black. The photo receptors on a digital camera's sensor are like buckets for light and you have to fill them up to get a proper exposure. A half full bucket and the image will be badly under exposed, and if the bucket gets too full then the image will be over exposed.

Without the flash the light bucket is almost completely empty.

So the flash is really the only source of light in an image like that one. Since the flash has an average duration of only 1/12000 of a second the flash becomes a virtual shutter -the fact that the actual shutter was open for 1/200 of a second doesn't matter, since there is very little natural light reaching the camera's sensor anyway.

So, in reality, I took the photo at about 1/12000 of a second. That’s why the image is sharp, even though I didn’t use a tripod. You can use the same “trick” to take photos of water drops (the subject of a future post).

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