<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
</head>
<body>
<p>Hello Hy,</p>
<p>I was planning on working on edits to the handbook but I recently
became obsessed with trying to build a camera sensor analyzer to
help determine read-noise values for cameras that do not include
it in the manufacturer documentation the way that ZWO and QHY
cameras do. <br>
</p>
<p>But I've attached a pdf that is a rough draft of docs for the
calculator, (not really complete yet, and some of it is now
incorrect due to some design changes), so the attached doc
probably won't fully answer all of your questions.</p>
<p>Yes, the filter bandwidth is nm. So 300 is essentially
luminance, RGB would be roughly 100, etc. <br>
</p>
<p>To help clarify, during my research on this exposure calculator
topic I came across a forum post with a chart. The photographer
in this case indicated that he was imaging in Bortle 5.5 skies, <b>but
with a f/3.0 optic</b>, he provided the following chart for his
exposures:</p>
<p><img src="cid:part1.0NIv82Fl.73fVju31@sbcglobal.net" alt=""></p>
<p>So you can see that his luminance exposure times with a gain of 0
with a Moravian C3 camera were just 13 seconds, (but he is only
running 561 exposures). When he runs with a gain of 2800 (which
is beyond a step-down in read-noise on his camera), the luminance
exposure time drops all the way down to 2 seconds. <br>
</p>
<p>His RGB exposures at gain 0, are just 39 seconds with 187
exposures per channel. He doesn't get into "long-ish" exposures
until he is running narrow-band.<br>
</p>
<p>That would lead us to your 2nd point. The stack time is merely
the product of the exposure time & number of exposures. This
would be analogous to the "signal". Stack noise represents the
total noise in the stack, but keep in mind that noise is reduced
in proportion to square root of the number of images. The ratio
column represents ratio of stack time to noise. So think of ratio
as being a simple measure of "quality" for the stacked image. But
my docs do not elaborate on a reasonable value for the ratio. My
understanding from posts about Dr Glover's calculations are that a
ratio greater than 80 would be considered extremely good, and a
ratio of 100 is excellent. <br>
</p>
<p>I was giving some thought altering the calculator grid display to
make it graphical. Perhaps allowing a user to select a desired
ratio, and the calculator simple would display a small chart to
better show whether the curve is reaching a point of diminishing
returns for an increase in stack time.<br>
</p>
<p>In your example I think that the calculation is showing that a
planned stack time of 20 hours may be a bit excessive; and that
your are basically onto the part of the curve where there is very
diminishing returns for the increase in stack size. You could
achieve a ratio of 100 on these 12 second luminance exposures with
just 12 hours of exposures. <br>
</p>
<p>But also consider that running the gain lower, maybe even at 0
might be reasonable in this case. The exposure times would rise
into the 30 second range and with the lower gain, the dynamic
range on the image should improve. Also be aware that the "noise
increase" value can be adjusted, 5% is recommended default. In my
opinion lowering the "noise increase" might make sense in your
case. <br>
</p>
<p>Also, in the chart from the forum post, the column listed for
"Noise Tolerance Factor C" is inversely related to the "noise
increase" control in this calculator. The Factor C value of 25 on
his chart is a noise increase of 2%, the Factor C value of 10 on
the chart is a noise increase of 5% . Given that that calculator
provided you with a exposure time that seems "short", you could
afford to reduce the Noise Increase %. <br>
</p>
<p>So, if you were to change to a 1% noise increase, and lowered the
gain to 0, the exposure time would rise to 170 seconds, and as a
result 11 hours of imaging, 232 exposures would produce a ratio of
100 in the stacked image. <br>
</p>
<p>And with regard to the excess precision on the UI, I agree I went
a bit extreme on decimal places. But as I was testing I was
frequently trying to match the calculator results with data I
found on images posted in forums. In some cases to match up those
values I needed the extra precision. I can certainly reduce the
precision in a future release.<br>
</p>
<p>One more comment... multiple instances of the calculator can be
run concurrently to allow for easy side-by-side comparisons with
alternate inputs. <br>
</p>
<p><br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 5/17/23 22:54, Hy Murveit wrote:<br>
</div>
<blockquote type="cite"
cite="mid:CA+B1P8tHnfuUOMOHFwQXnredm5QrzpYrjj0CV54k2grsXabWyQ@mail.gmail.com">
<meta http-equiv="content-type" content="text/html; charset=UTF-8">
<div dir="ltr">Joseph,
<div><br>
</div>
<div>Thanks so much for getting the exposure calculator up and
running in KStars. Impressive accomplishment!</div>
<div><br>
</div>
<div>I just tried using it, and have some questions/comments I
was hoping you could address.</div>
<div><br>
</div>
<div>Here's a screenshot, with questions below:</div>
<div><img src="cid:part2.VX0D4Kfs.4I0U8gL5@sbcglobal.net"
alt="Screenshot 2023-05-17 at 10.13.06 PM.png" class=""
width="370" height="542"></div>
<div>
<ul>
<li>I think I filled in the boxes appropriately above,
though not sure, please let me know. I tried these values:
sky quality 19 (about what I've measured at my house), f/8
reflector, full bandwidth (300nm), my ZWO ASI1600mm camera
at gain 75 (I assume it wants the gain I use for the 1600,
but I tried other values too), 20 total hours of exposure
time desired, default noise increase of 5%. It seems to be
telling me to take 5956 images each 12.09 seconds long,
which is obviously not a good answer. Am I doing something
wrong?</li>
<li>Not sure what Stack Time, Stack Noise, and Ratio mean.
Are shot noise and total noise in electrons? (Need
tooltips to help)</li>
<li>I was able to get it to give me a reasonable exposure
time (e.g. about a 2-minutes) if I set Noise Increase % to
0.4, but I really didn't know what to put in there, and so
used the default was 5%. Do you know, is 5% a good default
for the noise increase? Can we give more guidance on what
noise increase people should start with?</li>
<li>The tool needs better tooltips for pretty much each
value that needs to be entered. Most tooltips say "An
implementation of Dr Robin Glover's exposure calculation."
We can give credit elsewhere (e.g. usually done in "About
KStars"), but the tooltips should be informative. For
instance, is gain the actual gain values one enters for
the camera, or do you mean something like quantum
efficiency? Assuming it's the value entered to the
camera's driver, you should say that "Gain value used for
your camera". Filter Bandwidth should include units (e.g.
nm in this case.). </li>
<li>Don't need 3 decimal places for Sky Quality (make it one
or two decimals). Ditto for focal ratio. </li>
<li>Is there some documentation on use somewhere? E.g. can a
section be added to the handbook? Also, please start a
forum thread describing this new tool and how you
recommend users use it.</li>
</ul>
</div>
<div>Thanks again,</div>
<div>Hy</div>
<div><br>
</div>
<div><br>
</div>
</div>
</blockquote>
</body>
</html>