Re: Flicker?

Craig Miller (
Tue, 17 Jan 1995 13:17:40 -0500

At 11:42 AM 1/17/95, Michael Wakefield wrote:
>On Mon, 16 Jan 1995 wrote:
>> At 10:49 1/16/95, Patrick Delahanty wrote:
>> >Is there any way to reduce flicker when you point a camera at a Mac, PC, or
>> >TV?
>(lengthening the time for the scan) as a quick-and-dirty fix. Also, you
>may want to try changing the position of your zoom lens, as zooming in or
>out a little sometimes helps - I dunno why...

OK, here is why zooming can help/hinder the scan rate problem. Let's assume
that your camera is in the US, and takes approximately 65 miliseconds to
scan a single line (as it does in NTSC), and what you are shooting takes 70
milisecs to scan on a time line this would look like this:

Real Time

If by zooming way out on the PC screen you change the apparent scan rate of
the PC screen.

Zoom way out

By zooming to the 'magic' point you can get the apparent scan rate to be
close to the camera's scan rate.

Zoom to the magic point

Of course this will work best on similar things like a TV camera shooting a
TV screen, since the scan rates are essentually the same, but do not start
at the same time.

Hope this helps,


Craig Miller 808/539-3661
Digital Media Lab Coordinator 808/539-3833 fax
University of Hawaii

"To Web, or not to Web, that is the question...."