Histogram of ADU pixel values counted from a dark frame taken with exposure time 1s and ccd temperature -15 degrees. A gaussian fit has been fitted to the histogram.



Multiple histograms like the one above were made for various exposure times, the mean of their peaks were recorded and a scatter graph was made as above.

Conclusion: The points are overly scattered and the gradient is very small. We think this is due to the temperature of the ccd being too cold, at -15 degrees celcius. We reckon the ccd was working at 100% power to keep it at 15 degrees, as when we tried to go colder, it struggled to fall below -15. The dark frames were taken during the day and the dome was particularly hot which would also have affected the ccd's ability to cool down. Therefore, the ccd may have had a fluctuating temperature rather than a constant one, causing varying noise due to both temperature fluctuations and different exposure times.

Proposal: Try warmer temperatures, which could be kept more reliably constant.

Next, we tried a warmer temperature of 15 degrees, however, this led to too much noise, see histogram below.


Conclusion: The higher temperature led to a more complicated histogram due to excessive noise. The histogram requires a much more complicated fit.

Proposal: Obtain data from the middle point, around -5 to 10 degrees.

So, we made another dark frame, opting for a longer exposure time of 15 minutes, which led to the following image. Interesting effect of darker sides and brighter middle, and pixels bleeding down. This may be due to the overlong exposure time.


Proposal for next week: Take more dark frames at 5 degrees or there about, with shorter exposure times than 15 minutes.

-- LunaBorella - 13 Oct 2017

Topic attachments
I Attachment Action Size Date Who Comment
PNGpng 15degreesHistogram.png manage 32.0 K 13 Oct 2017 - 00:45 BekiChafer Histogram of pixel ADU values in a dark frame with Exp time 60s and temp 15 deg
PNGpng 1secGraph.png manage 53.8 K 13 Oct 2017 - 00:02 LunaBorella  
Unknown file formatFIT 5Deg_15mins.FIT manage 3054.4 K 13 Oct 2017 - 00:57 BekiChafer Dark frame at 5 degrees and exposure time 15 minutes.
JPEGjpg 5Deg_15mins.jpg manage 241.6 K 13 Oct 2017 - 01:01 BekiChafer Dark frame at 5 degrees and exposure time 15 minutes.
Compressed Zip archivezip HistogramFitGraphs.zip manage 360.1 K 13 Oct 2017 - 00:06 LunaBorella  
PNGpng SigmaVsExposurefit.png manage 42.5 K 13 Oct 2017 - 00:03 LunaBorella  
PNGpng meanVsExposurefit.png manage 37.9 K 13 Oct 2017 - 11:49 LunaBorella  

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Topic revision: r3 - 13 Oct 2017 - LunaBorella

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