Re: Flicker?

Craig Miller (cvmiller@uhunix.uhcc.hawaii.edu)
Tue, 17 Jan 1995 13:17:40 -0500


At 11:42 AM 1/17/95, Michael Wakefield wrote:
>On Mon, 16 Jan 1995 msattler@jungle.com 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
cam
|---------------->|
PC
|------------------->|

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

Zoom way out
cam
|---------------->|
PC
|-------->|

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
cam
|---------------->|
PC
|-------------->|

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...

------------------------------------------------------------------------------
Craig Miller 808/539-3661
Digital Media Lab Coordinator 808/539-3833 fax
University of Hawaii cvmiller@uhunix.uhcc.hawaii.edu

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