Date: Thu, 23 May 2002 10:56:47 -0500 (CDT)

Author: Paul Nord

Subject: Re: Lookin at Laser Discs



Many video cameras have an adjustable "Shutter Speed". It's basically the
time between when the CCD is cleared and then read. If it is as low as
1/60th of a second, then even slowly moving objects will look blured. A
standard video signal will only update at the rate of 30 images per
second (or is it 60?). But if the CCD is collecting all the time, moving
objects will be blurred.

We bought a nice fancy camera with a large lens and fancy editing
features. But we sent it back when we found that the "Sports Mode" would
only come on automatically when the camera thought that the action was
fast. Needless to say, the projectile motion lab did not switch the thing
into "Sports Mode" in the 2 seconds then ball was moving across the
screen. The ball moves about 10 inches in 1/60th of a second. So, it
looked like a big long line on the screen. We got the next cheeper model
camera which has an adjustable "Shutter Speed". I can set it between 1/60
and 1/2000th of a second. 1/250th is good enough for the projectile and
air table experiments.


On Thu, 23 May 2002, George M. Caplan wrote:

> Date: Thu, 23 May 2002 10:12:04 -0400
> From: George M. Caplan
> Reply-To:
> To:
> Subject: Lookin at Laser Discs
> Thanks to you folks, I have found the "inertial ball" demonstration (I
> think it's 2-13)
> in the Video Library of Physics.
> When I step through the "fast pull" the picture is blurry when the motion
> is fast. Here's my theory
> about this: I think I am being shown both fields of the video (i.e. an
> entire frame) so half of
> the lines were taken 1/60 sec after the other half, and this accounts for
> the blur.
> Does this make sense? I don't think the blur is caused the same way the
> blur would be caused on
> photographic on film.