Questions about read out noise and gain
lin wrote on Mar 26, 2009
Hi, everyone
During my work with IRAF, I find that
In Zerocombine or Flatcombine task, there are:
(rdnoise= ) ccdclip: CCD readout noise (electrons)
(gain = ) ccdclip: CCD gain (electrons/DN)
But in Apall task, there are
(readnoi= ) Read out noise sigma (photons)
(gain = ) Photon gain (photons/data number)
It seems that stand for different meaning. Does that two have any relation? and How can i set these parameters better?
Thanks!
During my work with IRAF, I find that
In Zerocombine or Flatcombine task, there are:
(rdnoise= ) ccdclip: CCD readout noise (electrons)
(gain = ) ccdclip: CCD gain (electrons/DN)
But in Apall task, there are
(readnoi= ) Read out noise sigma (photons)
(gain = ) Photon gain (photons/data number)
It seems that stand for different meaning. Does that two have any relation? and How can i set these parameters better?
Thanks!
Guest wrote on Mar 26, 2009
Hi,
From what I learn about photoelectric effect (modern physics class), one photon = one electron. Unless Iraf has some other interpretation.
8)
From what I learn about photoelectric effect (modern physics class), one photon = one electron. Unless Iraf has some other interpretation.
8)
James Turner wrote on Mar 26, 2009
The number of incident photons per electron is the quantum efficiency of the detector and is <100%, just because the detector isn't perfect. However, what matters is what you are actually counting, ie. electrons (or "detected photons"). I'm pretty certain that zerocombine and apall mean the same thing, which is really electrons (== photons registered by the detector).
Cheers,
James.
Cheers,
James.
Guest wrote on Mar 26, 2009
Hi Lina and James,
Isn't quantum efficiency the number of electrons divided by the number of incident photons? There would be more incident photons than electrons released in the material.
By the way, I agree that zerocombine and apall are talking about the same thing, otherwise I will have to redo all my data reduction.
As for Lina, probably you can get the readnoise and gain from the CCD specification .
cheers,
Siti :)
Isn't quantum efficiency the number of electrons divided by the number of incident photons? There would be more incident photons than electrons released in the material.
By the way, I agree that zerocombine and apall are talking about the same thing, otherwise I will have to redo all my data reduction.
As for Lina, probably you can get the readnoise and gain from the CCD specification .
cheers,
Siti :)
James Turner wrote on Mar 26, 2009
sitij109
Isn't quantum efficiency the number of electrons divided by the number of incident photons?
Yes, sorry!
James.
lin wrote on Mar 26, 2009
Hi,
Thanks very much!!
BTW: I am redoing my data reduction now, because during my three times observation, the values of readout noise and gain were set different, but I didn't notice that and set gain=1 before....
I must be more careful and patient.
Thanks very much!!
BTW: I am redoing my data reduction now, because during my three times observation, the values of readout noise and gain were set different, but I didn't notice that and set gain=1 before....
I must be more careful and patient.
Francisco Valdes wrote on Mar 26, 2009
Hi,
I apologize for any inconsistency in nomenclature. Yes, in those tasks photons really means the detected photoelectrons. For optical CCDs there is basically a 1:1 correspondence. The main reason to put it this way was to indicate whether one is talking about data numbers or electrons with the gain part removed. In other words
Yours,
Frank Valdes
I apologize for any inconsistency in nomenclature. Yes, in those tasks photons really means the detected photoelectrons. For optical CCDs there is basically a 1:1 correspondence. The main reason to put it this way was to indicate whether one is talking about data numbers or electrons with the gain part removed. In other words
electrons=DN*gainYours,
Frank Valdes
Last post on Mar 26, 2009