Running on Water

Started 3 months ago | Discussions thread
Stephen McDonald
Stephen McDonald Forum Pro • Posts: 14,412
Blurring in Still and Moving Images

One thing that should be considered regarding the blurred wingtips of flying birds in photos, is that human vision produces blurring in such subjects when viewing them live. Like video or motion-picture cameras, human vision captures and processes a series of still images. The refresh rate of the frames for our vison varies between about 15 to 80 frames-per-second (FPS), depending mostly on the amount of light available.

So even if the light and moving-image playback is bright, our highest visual FPS would not allow us to see unblurred wings of flying birds. But this is normal and we wouldn't notice anything wrong about fast-moving subjects as we see them. Although it's nice to have sharp and unblurred wingtips in photos, we are seeing something that we would not, in live vision. This is an area in which photography takes us beyond normal vision.

In fact, if the video shutter speed is too fast when shooting flying birds, a strobing effect may be produced, where the wings appear to be in several places at once. Typically, video of flying birds works best when the fractional number of the shutter speed is no more than about twice the frame rate. If you're shooting such a subject at 30 FPS, a shutter speed of no more than 1/60th-second is best. Then the wingtips will appear blurred in playback, as we would naturally see them.

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