Re: videotape data on free fall

[brian whatcott <inet@intellisys.net>]

At 10:23 10/27/97 -0500, James Wheeler wrote:
> In some cameras the way in which fast shutter speeds are attained is by
> sweeping a slit across the face of the film.  The film is only exposed
> when the slit is in front of it.  Thin, fast moving slits make for short
> exposures. 

This is called the 'focal plane' shutter; two blinds with a variable gap,
which these days may be computed by a through-the-lens photometer in the 
'aperture-priority' cameras. The 'shutter-priority' cameras vary the 
aperture automatically by similar means.

> Is this how a cam corder works?  

No

> Is this relevent to producing
> "clean" images of fast moving objects?  

Yes, the test which Leigh mentioned, and which Ludwik knows about,
is to shoot a revolving disk. Preferably one attached to an induction or
synchronous motor which spins at about 3600 rpm.
 A straight radial line is curved by a focal plane shutter - or an electronic
sensor with a prolongued image acquisition time.
 A slow shutter will additionally blur the image.

> Does the orientation of the camera
> matter?

This is a second order effect.

Regards

brian whatcott <inet@intellisys.net>
Altus OK