Kstars-devel Digest, Vol 229, Issue 1

Sun Mar 5 23:28:31 GMT 2023

Using the correct exposure time is important for variable stars and exoplanet transits.  My approach is to take a sample exposure and measure the pixel count of the target star and suitable comparison stars in the field.  I use AstroImage J to draw a circle around a star and then do a measure.  This gives me min, max and mean values for the pixels inside the circle. Its important not to get saturated pixels and to keep the maximum pixel count in the linear region of the sensor, say 30,000 - 40, 000 ideally. It would save me a lot of time if a similar tool was available in the Fits viewer.

I would have a go of developing this but not in a position to compile code.  Is there any Kstars training available to help set up a windows desktop and compile code. I tried Qt on Windows but it got very complicated compiling in Ubuntu.  Whats the best way to get started?

Regards

David

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Today's Topics:

   1. Optimal Exposure and Noise Calculator (joseph.mcgee at sbcglobal.net)

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Message: 1
Date: Fri, 3 Mar 2023 09:16:09 -0800
From: "joseph.mcgee at sbcglobal.net" <joseph.mcgee at sbcglobal.net>
To: kstars-devel at kde.org
Subject: Optimal Exposure and Noise Calculator
Message-ID: <1fbb5bde-1e74-ab97-c24a-07091ad9b36e at sbcglobal.net>
Content-Type: text/plain; charset="utf-8"; Format="flowed"

Hi All,

I'm a retired software developer (mostly Java, C, and some C++). I've been using KStars on a Raspberry Pi (Ubuntu), since I got interested in AP, (around 2020).  Back in late 2021 I wrote an optimal exposure time calculator (in Java), based on the work of Dr Glover.  I just got to thinking that it might be a nice addition to KStars, and today I found a request for it: 
https://indilib.org/forum/wish-list/5300-exposure-calulator.html?start=12

My current code is pretty simple but has no user interface.  It uses a few classes for configuration, a table of sensor gain to read noise, observation site location SQM value, optics F ratio data, and
(experimentally) a filter bandpass table.  The code just iterates through all the combinations of the inputs to output tab delimited data to the console, that I copy into a spreadsheet.

Keep in mind that the exposure time calculations are optimal (per Dr Glover), but not necessarily practical.  I've seen a slow optic, with a filter, in very dark skies,  produce a optimal sub exposure time calculation that exceeded 3 hours.

If this were integrated into KStars, we would obviously need to provide a means for a user to input some of their own configuration information.

Please let me know if you'd like to consider integrating this into KStars, (I would need coaching/help if I were to take this on).

Example output:

I have my code configured for the read noise for my main imaging camera, (a ZWO ASI-071 Color), SQM data for four observation sites.  F ratios for four optics, and bandpass info for two filters.  And I'm using an allowable noise increase of 5%.

A small section of the output provides this information for a given site, optic, and sensor gain selection:

*Site Name:*

Chuchupate

*Sky Quality:*

21.65

magnitude per arc-second2

*Light Pollution Base Rate:*

19.6

e per second

*Optic Name:*

Esprit 100

*Light Pollution Rate:*

0.65

e per second for f/5.5 optic

*Camera Sensor Gain:*

50

*Read Noise:*

2.78

*Filter*

*Optimal Sub-exposure (sec)*

*Shot pollution electrons*

*Exposure shot noise*

*Exposure total noise*

No Filter

349.1

226.2

15

15.3

Optolong l-Pro

634.8

411.3

20.3

20.5

Optolong l-Enhance

3174

2056.3

45.3

45.4

And accumulated data for imaging sessions of 1 to 5 hours:

*3,600.00 seconds*

*7,200.00 seconds*

*10,800.00 seconds*

*14,400.00 seconds*

*18,000.00 seconds*

*Filter*

*Exposure Count*

*Stack Total Time*

*Stack total noise*

*Exposure Count*

*Stack Total Time*

*Stack total noise*

*Exposure Count*

*Stack Total Time*

*Stack total noise*

*Exposure Count*

*Stack Total Time*

*Stack total noise*

*Exposure Count*

*Stack Total Time*

*Stack total noise*

No Filter

10

3491.44

48.37

21

7332.03

70.09

31

10823.47

85.16

41

14314.92

97.93

52

18155.51

110.29

Optolong l-Pro

6

3808.85

50.14

11

6982.89

67.89

17

10791.73

84.4

23

14600.58

98.17

28

17774.62

108.31

Optolong l-Enhance

1

3174.04

45.43

2

6348.08

64.25

3

9522.12

78.69

5

15870.2

101.59

6

19044.24

111.29

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