[Elphel-support] Elphel NC353L long exposures

[Andrey Filippov]

Hello Niko,

For very long exposures it is better to turn autoexposure off and set
exposure time manually using "Parameter Editor" (
http://192.168.1.48/index.php?site=autocampars.php if the camera has
default IP). Select "autoexposure" group, uncheck "Include image" (for
faster updates) and open link "View/edit current" - there you can disable
autoexposure and set exposure time (in microseconds). Camera will seem to
be "frozen" because all parameters are updated at frame sync interrupts.
You may update image with the link http://192.168.1.48:8081/bimg - it is
independent of the main web server and will not freeze if the camera will
be waiting for the next image. Exposure time update will take several
frames.
You may also telnet to the camera (using login:root password:pass) and view
raw sensor registers (described in the Aptina datasheet), exposure time is
in registers 8 and 9, total exposure time will be (reg8*2^16+reg9)*line
scan time. You may view the current settings with the command:
 fpcf -i2cr16 4808 2
All 256 registers:
 fpcf -i2cr16 4800 100
Andrey
For very long exposures the fixed pattern noise will be significant, you'll
have to subtract it.

Andrey
On Tue, Aug 14, 2012 at 7:37 AM, Niko Lavonen <nlavonen at kurp.hut.fi> wrote:

> Hello,
>
> We here at Metsähovi Radio Observatory acquired an NC353L camera earlier
> this summer for all-sky monitoring of weather conditions. Overall we've
> been pleased with the camera, but there is a problem with long exposures
> we've not been able to figure out. It seems the camera won't do exposures
> longer than approximately 38 seconds. Is there a known limitation in the
> camera's hardware or software that imposes this limit? To get a view of the
> night sky, we'd very much like to have the camera do exposures for up to
> many minutes if needed.
>
> We've observed that when the camera reaches the "maximum" exposure time,
> it starts reporting that the exposure is 1/1000000 seconds, while it can be
> seen from the images that the actual exposure is still in the order of many
> sedconds. We've tried raising the AUTOEXP_EXP_MAX value higher than the ~38
> second limit, but the camera won't go higher. We've also tried manually
> setting the exposure time to e.g. 60 or 120 seconds, but in these cases the
> camera has frozen. Our camera firmware version is 8.2.7.
>
> Regards,
>
> Niko Lavonen
> Research assistant
> Aalto University Metsähovi Radio Observatory
> Metsähovintie 114, 02540 Kylmälä, Finland
> e-mail: nlavonen at kurp.hut.fi
> Phone: 029-4424856
>
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