Topics

1

Electronics / sensor Signal−to−Noise Ratio

« on: April 24, 2018, 06:18:13 PM »

Hi all

I was wondering whether someone ever characterized the noise of the sensor used on the miniscope, for example by measuring the Photon Transfer Curve (https://www.adimec.com/how-to-measure-the-photon-transfer-curve-for-ccd-or-cmos-cameras/).

Plotting the log of the  Standard Deviation versus the log of the average effective signal , one would expect to see a region where the photon shot noise is dominant, and the slope of the curve is equal to 0.5.

I measured this curve and identified a portion of the curve where the slope is 0.5 (STD~(MEAN)^(0.5)). This was roughly between the values 1 and 50 (at gain 4x). But to my surprise there is also another portion (much larger) which has a very different regime. In this portion, extending from the values 50 to ~200, I see the STD varying linearly with the MEAN.
Finally the curve ends as expected (values 200-255): the STD drops to zero as the pixels saturate.

I do not understand the linear relationship between STD and MEAN at the intermediate light levels.
Did anyone ever made this measurement? Did you observe the same thing?

Thanks for your help,
Stephan

2

Electronics / larger CMOS sensor?

« on: November 17, 2016, 07:35:59 PM »

Hi Daniel,
I was wondering whether you know of another CMOS sensor that could potentially be used (after redeveloping a new board of course) and having a ~square active surface, roughly twice as large as the current CMOS sensor.
Thanks,
Stephan

3

DAQ Software/Firmware / dropped frames

« on: October 19, 2016, 09:53:46 PM »

Hi Daniel,

I observe dropped frames at regular intervals (when running at 60fps, there one or more dropped frames every ~75 frames as measured from the sync output; when running at 30fps, there are  several dropped frames every ~148 frames).
It comes at very regular intervals. Have you ever encounter that? Any idea what is going on?

Although there are definitely dropped frames, the software does not detect them and the "dropped frame counter" remains at zero.

Thanks,
Stephan

PS: in the current implementation I did not connected a LED to the camera board. I am running the system with an externally connected LED.