| ToUCam Pro
exposure time Philips ToUcam Pro is a
very good camera for astrophotography. For image analysis
it is important to know exact exposure time. By using the
camera you can discover soon that the exposure time set
in camera's control panel doesn't conform the real
exposure time.
So I decided to measure the real exposure time.
1, Important camera controls
2, Measuring setup
3, Measured results
4, Exposure table for
ToUcam Pro
1,
Important camera controls
Frame rate settings and image controls
The frame rate is important for achieving good picture
quality. The lower the frame rate, the higher is picture
quality. I usally use 5fps, sometimes 10fps. 15fps
noticably affect the quality (look at my picture quality tests)
White balance and exposure controls - shutter speed and
gain:
2,
Measuring setup
Here is my exposure measuring setup:
TV screen shows digits, each digits is displayed
in one frame - i.e. 40ms. |
In Corel PhotoPaint
I created a set of 25 bitmaps with numbers. Each
bitmap corresponds to 1 frame and contains one
digit highlighted. I load the sequence to K3CCDTools
and generated AVI sequence with frame rate 25fps.
Then I load the sequence into VirtualDub and
appended it several times untile I had 20 minutes
of video.
Usually I play the sequence directly to computer
video output connected to TV set. The measured
cameras are connected to laptop and capture the
TV screen.
However, ToUCam Pro is not compatible with my
laptop so I had to connect it to my desktop
computer. That's why it was necessary to record
the AVI sequence to videorecorder (it is not
possible to exactly play video to TV output and
record AVI from webcam simultaneously).The
principle of measuring is simple. When exposure
time is e.g. 1/5s (200ms), then you should see 5
highlighted digits. It may differ one digit,
because TV set and webcam are not synchronized.
However for our purpose the precision is fine
enough
|
Measuring AVI sequence. |
3,
Measured results
| Conditions |
Measured screen (1 second) |
Frame rate & Exposure |
Real Exposure |
Camera controls:
5fps, exposure 1/25s
Captured at 5fps |
 |
 |
1/5s |
Camera controls:
5fps, exposure 1/33s
Captured at 5fps |
 |
 |
1/10s |
Camera controls:
5fps, exposure 1/50s
Captured at 5fps |
 |
 |
1/15s |
Camera controls:
5fps, exposure 1/100s
Captured at 5fps |
 |
 |
? |
Camera controls:
10fps, exposure 1/25s
Captured at 10fps |
 |
|
1/10s |
Camera controls:
10fps, exposure 1/33s
Captured at 10fps |
 |
|
1/15s |
Camera controls:
10fps, exposure 1/50s
Captured at 10fps |
 |
|
? |
Camera controls:
15fps, exposure 1/25s
Captured at 15fps |
 |
|
1/15s |
Camera controls:
15fps, exposure 1/33s
Captured at 15fps |
 |
|
? |
Camera controls:
15fps, exposure 1/50s
Captured at 15fps |
|
|
? |
4,
Exposure table for ToUcam Pro
| Frame Rate |
Shutter Slider |
Real Exposure |
| 5fps |
1/25s |
1/5s |
| 5fps |
1/33s |
1/10s |
| 5fps |
1/50s |
1/15s |
| 5fps |
1/100s |
? |
| 10fps |
1/25s |
1/10s |
| 10fps |
1/33s |
1/15s |
| 10fps |
1/50s |
? |
| 10fps |
1/100s |
? |
| 15fps |
1/25s |
1/15s |
| 15fps |
1/33s |
? |
| 15fps |
1/50s |
? |
| 15fps |
1/100s |
? |
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permission of author.
Last Update:
15.10.2003
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