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Re: Photon Transfer Curve

Subject: Re: Photon Transfer Curve
From: "Jens Dierks" <me@xxxxxxxxxxx>
Date: Tue, 19 Dec 2006 18:35:01 +0100
Newsgroups: sci.astro.ccd-imaging
Hi Patrick,

>> So the readout noise is more a quantization noise.
>
> I believe some of it may be.

If it doesnt decrease with another board, you have to rethink the
way you gain the data.
I dont know how the darklevel of each pixel is sampled in a cmos
sensor. But in my understanding, it has to be sampled just close
bevor the lightlevel, or has to be integrated for a longer time
to get rid of the low frequencies of the amp-noise.


> That drawing IS good.  It is quite similar to what I see.  So, it looks
> like I just never reach the shot-noise region.

Yes, but in the case that the read-noise increases with a longer
exposure time (and the brighter images were captured with longer
exposures), it would maybe pointing to a wrong darklevel acquisition.


>> I dont know how much saturation can flatten the slope, but 0.2?
>>
>
> I would expect the characteristic steep fall off of the curve at
> saturation.

Yes, if the converter is saturating bevor the sensor gets close
to the fullwell.
Otherwise it shouldnt fall off so quick, dependend on the sensors
characteristic. Ok, 760e noise_rms is nothing against 500ke fullwell,
so it wouldnt flatten the curve a lot, too.

Best regards,
Jens



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