Freeze Frame Exposure Time?

Is there some standard amount of exposure time for a "video camera/capture card"
freeze frame? If so, what is it? I have a Supercircuits PC23C and a Hauppauge WinTV
GO capture card.
--
Wayne T. Watson (121.015 Deg. W, 39.262 Deg. N, 2,701 feet, Nevada City, CA)
-- GMT-8 hr std. time, RJ Rcvr 39° 8' 0" N, 121° 1' 0" W

"Don't hassle me with your signs, Chuck" -- Peppermint Patty, Peanuts

Web Page: home.earthlink.net/~mtnviews
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On Thu, 04 Mar 2004 06:03:03 GMT, "W. Watson" wrote:

Is there some standard amount of exposure time for a "video camera/capture card"
freeze frame? If so, what is it? I have a Supercircuits PC23C and a Hauppauge WinTV
GO capture card.

No. Most video cameras will adjust their exposure time automatically, typically
from a maximum of 1/30 second to a minimum of 1/1000 of a second, or shorter.
The frame is captured over 1/30 second regardless of the exposure time. This is
the behavior of the PC23C unless you have modified it for manual exposure
control (a simple mod, highly recommended if you use the camera for astronomical
imaging).

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:

On Thu, 04 Mar 2004 06:03:03 GMT, "W. Watson" wrote:


Is there some standard amount of exposure time for a "video camera/capture card"
freeze frame? If so, what is it? I have a Supercircuits PC23C and a Hauppauge WinTV
GO capture card.


No. Most video cameras will adjust their exposure time automatically, typically
from a maximum of 1/30 second to a minimum of 1/1000 of a second, or shorter.
The frame is captured over 1/30 second regardless of the exposure time. This is
the behavior of the PC23C unless you have modified it for manual exposure
control (a simple mod, highly recommended if you use the camera for astronomical
imaging).

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
Yes, I modified it per Paul Goelz's web page instructions. I take it then that the
mod standarized it to roughly 1/30th of a second for a single frame? If so, then I
would guess if my software is set to shoot for say 10 frames/sec. in video mode, then
each shot is roughtly 1/10th of a second--less for download considerations.

--
Wayne T. Watson (121.015 Deg. W, 39.262 Deg. N, 2,701 feet, Nevada City, CA)
-- GMT-8 hr std. time, RJ Rcvr 39° 8' 0" N, 121° 1' 0" W

"Don't hassle me with your signs, Chuck" -- Peppermint Patty, Peanuts

Web Page: home.earthlink.net/~mtnviews
sierra_mtnview -at- earthlink -dot- net
Imaginarium Museum: home.earthlink.net/~mtnviews/imaginarium.html

On Thu, 04 Mar 2004 12:21:38 GMT, "W. Watson" wrote:

Yes, I modified it per Paul Goelz's web page instructions. I take it then that the
mod standarized it to roughly 1/30th of a second for a single frame? If so, then I
would guess if my software is set to shoot for say 10 frames/sec. in video mode, then
each shot is roughtly 1/10th of a second--less for download considerations.

There are several modifications possible with the PC23C. Normally, you would
want to disable the AGC circuit so the camera's video amplifier operates at a
fixed gain. Then you would want to provide manual adjustment for the shutter
speed. (Normally, both the gain and shutter speed are managed automatically, and
in unison, to control sensitivity). When you have manual control of the shutter
speed, you can set it to be anything from 1/30 second to 1/100,000 second. No
matter what shutter speed you have set, the camera output is RS-170, or 30
frames per second (really, one subframe each 1/60 second). If you set your video
capture software for 10 frames per second, that has no effect on the exposure
time- it will still be between 1/30 and 1/100,000 second depending on the
shutter speed setting your mod is providing the camera. In other words, the
camera has no idea what your video capture rate is- it just outputs 30 frames
per second no matter what, and exposes each of those frames for a period
determined either by its internal auto exposure circuit or by the voltage
supplied by your external mod.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Hi,
Thanks. Interesting.

I called SC in Texas awhile ago and posed the question of specifying 100 frames a
second (video mode). My understanding from the tech guy is that one would get 30
frames, but each exposure would be at most 1/100th sec. Similarly, specifying 500
frames a second would produce nothing greater than 1/500th sec. I'm not so sure I buy
that, especially in view of what you said below. If you're right, and you probably
are, then I have a feeling there are a number of people out there who think they are
shooting at (specified) speeds of 1/100th, 1/500th, 1/4000th, etc. with their video
cameras.

Chris L Peterson wrote:

On Thu, 04 Mar 2004 12:21:38 GMT, "W. Watson" wrote:


Yes, I modified it per Paul Goelz's web page instructions. I take it then that the
mod standarized it to roughly 1/30th of a second for a single frame? If so, then I
would guess if my software is set to shoot for say 10 frames/sec. in video mode, then
each shot is roughtly 1/10th of a second--less for download considerations.


There are several modifications possible with the PC23C. Normally, you would
want to disable the AGC circuit so the camera's video amplifier operates at a
fixed gain. Then you would want to provide manual adjustment for the shutter
speed. (Normally, both the gain and shutter speed are managed automatically, and
in unison, to control sensitivity). When you have manual control of the shutter
speed, you can set it to be anything from 1/30 second to 1/100,000 second. No
matter what shutter speed you have set, the camera output is RS-170, or 30
frames per second (really, one subframe each 1/60 second). If you set your video
capture software for 10 frames per second, that has no effect on the exposure
time- it will still be between 1/30 and 1/100,000 second depending on the
shutter speed setting your mod is providing the camera. In other words, the
camera has no idea what your video capture rate is- it just outputs 30 frames
per second no matter what, and exposes each of those frames for a period
determined either by its internal auto exposure circuit or by the voltage
supplied by your external mod.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com


--
Wayne T. Watson (121.015 Deg. W, 39.262 Deg. N, 2,701 feet, Nevada City, CA)
-- GMT-8 hr std. time, RJ Rcvr 39° 8' 0" N, 121° 1' 0" W

The human body is 2/3rds water.
Think about that the next time you pee.

Web Page: home.earthlink.net/~mtnviews
sierra_mtnview -at- earthlink -dot- net
Imaginarium Museum: home.earthlink.net/~mtnviews/imaginarium.html

On Thu, 04 Mar 2004 22:54:23 GMT, "W. Watson" wrote:

I'm surprised a 'common' web camera would have that much flexibility, i.e., exposure
time and frame rate. What's the need there? Does it have something to do with color?
Perhaps it simplifies the frame grabber?

A web camera is a camera and framegrabber integrated into one unit. Naturally,
that gives lots more control than a framegrabber alone, which is limited to
RS170/NTSC/PAL video formats.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com