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List:       kstars-devel
Subject:    Re: Optimal Exposure and Noise Calculator
From:       Jens Scheidtmann <jens.scheidtmann () gmail ! com>
Date:       2023-03-06 15:39:08
Message-ID: CADfVb55si-6rDa37byJzjrVSf1uRPrxO5ZaMbY78pEQ7axpNjQ () mail ! gmail ! com
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Hi Joseph,

Am So., 5. M=C3=A4rz 2023 um 06:07 Uhr schrieb joseph.mcgee@sbcglobal.net <
joseph.mcgee@sbcglobal.net>:

> [...]
> You raised a suggestion that bias frames could be used to determine
> sensor read noise.  I must be missing some knowledge in this area. I
> just ran a test with my planetary camera (ASI-178), where I captured a
> set of bias frames incrementing the gain from 0 to 400 in steps of 50,
> with an exposure time 32us, (I believe that is the lower limit for the
> ASI-178).  I then used a tool that can assess noise in the image.  The
> noise measured in each image increased as the gain increased; so this
> did not match the downward trend I expected from the ZWO read-noise graph=
.
>
>
Bias frames capture the read-out noise of the electronics in ADUs
(analog/digital converter units). When you're changing the gain, you're
also changing the ADU~electron relationship. Manufactureres also have a
graph for that. You at least have to use the respective chart to convert
that reading to e-rms.

Jens

[Attachment #3 (text/html)]

<div dir="ltr"><div>Hi Joseph,</div><br><div class="gmail_quote"><div dir="ltr" \
class="gmail_attr">Am So., 5. März 2023 um 06:07  Uhr schrieb <a \
href="mailto:joseph.mcgee@sbcglobal.net">joseph.mcgee@sbcglobal.net</a> &lt;<a \
href="mailto:joseph.mcgee@sbcglobal.net">joseph.mcgee@sbcglobal.net</a>&gt;:<br></div><blockquote \
class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid \
rgb(204,204,204);padding-left:1ex">[...]<br> You raised a suggestion that bias frames \
could be used to determine <br> sensor read noise.   I must be missing some knowledge \
in this area. I <br> just ran a test with my planetary camera (ASI-178), where I \
captured a <br> set of bias frames incrementing the gain from 0 to 400 in steps of \
50, <br> with an exposure time 32us, (I believe that is the lower limit for the <br>
ASI-178).   I then used a tool that can assess noise in the image.   The <br>
noise measured in each image increased as the gain increased; so this <br>
did not match the downward trend I expected from the ZWO read-noise graph.<br>
<br></blockquote><div><br></div><div>Bias frames capture the read-out noise of the \
electronics in ADUs (analog/digital  converter units). When you&#39;re changing the \
gain, you&#39;re also changing  the ADU~electron relationship. Manufactureres also \
have a graph for that. You at least have to use the respective chart to convert that \
reading to e-rms.  </div><div><br></div><div>Jens</div></div></div>



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