How Is a Dark Frame Taken in CCD Cameras?

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Discussion Overview

The discussion focuses on the process of taking dark frames in CCD cameras and the methods for determining camera efficiency as a function of energy. It encompasses technical explanations and practical applications relevant to research in CCD technology.

Discussion Character

  • Technical explanation
  • Exploratory

Main Points Raised

  • One participant inquires about how a dark frame is taken, suggesting it may be the state of the pixel array when the shutter is closed.
  • Another participant confirms that a dark frame should be taken with the same exposure as the actual image.
  • There is a question about determining camera efficiency as a function of energy, with a suggestion that this may relate to Quantum Efficiency and the need for a standard brightness source or a calibrated camera for comparison.
  • A participant mentions using an iron-55 source to measure charge transfer efficiency, noting that it creates a fixed number of electrons per event, which can be measured in adjacent pixels.
  • Another method discussed involves using the iron-55 source to measure gain by comparing numbers in images to actual electrons in the CCD.
  • A recommendation is made for a review article on CCDs that may be more accessible than the referenced book by Janesick.

Areas of Agreement / Disagreement

Participants generally agree on the method for taking dark frames and the relevance of using standard sources for efficiency measurements, but there are varying details on the specific methods and parameters involved, indicating some unresolved aspects of the discussion.

Contextual Notes

Participants reference specific measurement techniques and sources, but there may be limitations related to the accessibility of certain materials and the assumptions underlying the methods discussed.

Pingona
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Hello,

I have two question regarding CCD camera technology.

How is a dark frame(image) taken ? ( Is this simply the state of the pixel array when the shutter is in close position?

How can one determine the camera efficiency as a function of energy from energy dependent measurements? What data or parameters should I look into for this analysis.

Thank you
 
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Pingona said:
Hello,

I have two question regarding CCD camera technology.

How is a dark frame(image) taken ? ( Is this simply the state of the pixel array when the shutter is in close position?

How can one determine the camera efficiency as a function of energy from energy dependent measurements? What data or parameters should I look into for this analysis.

Thank you

What is the context of your question? Is this for research, or industrial application, or a school report? What reading have you done up to now, and can you point us to some of those information resources?
 
Research work. I am reading the book by James Jainseck on CCD technology. what we have is images from a CCD camera
 
Pingona said:
How is a dark frame(image) taken ? ( Is this simply the state of the pixel array when the shutter is in close position?
Yes, you generally want to take a dark with the same exposure as the real image.

How can one determine the camera efficiency as a function of energy from energy dependent measurements?
if you mean the Quantum Efficiency then you need a standard brightness source (or another calibrated camera to compare it against).
Charge transfer efficency you can do with an iron 55 source, the radiation creates a fixed number of electrons per event - you can then measure the measured signal in adjacent pixels.

You can also use the fe55 to measure the gain (numbers in your image compared to real electrons in the CCD) - there is also a signal variance technique you can do with real data

I don't know how easy it is to get online but there is an excellent review of CCDs in "MacKay, C.D. 1986, Annual Review Astronomy&Astrophysics 24, 255, “Charge-coupled devices in astronomy” it's a lot more readable than Janesick's book
 

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