Sqm measurements don’t make sense

[emma0223]

Are your sqm readings making sense? My camera is located in a city with bortle 8-9sky and I’m getting readings of 22-24mag/arcsec^2 which don’t make sense, number should be way lower on light polluted sky’s or am I wrong?

[aaronwmorris]

I have not quite been able to nail down the SQM values. I have had several discussions over time, but it has been a very difficult topic to crack.

The intent is for the readings to be magnitude arcsec^2, but it is just the average ADU of the image for now.

[emma0223]

Thanks for clearing that up, would a tsl237 photodiode not be a better option for the magnitude reading ? Only problem is finding one

[aaronwmorris]

The jSQM value is calculated from the image data, but indi-allsky actually supports more modern Lux sensors like the TSL2591, VEML7700, etc. There is a different SQM variable that is closer to the magnitude measurement when using one of these.

I actually have a TSL237 in my inventory (from radio shack), but it is becoming a rare find.

[emma0223]

I have a tsl237 somewhere here but, Since we’re talking about sensors, is the max sensor input 3 ? Could a 4th sensor be added ? I only see 3 sensor in the config page

[aaronwmorris]

The tsk237 is just a challenging sensor to manage with a non-realtime OS like Linux.

3 sensors just felt like a good value, but more could be added. Every sensor just has have additional support code to manage it.

Keep in mind every sensor can have multiple data points, so a temperature sensor can return, temp, humidity, pressure, etc.