SQM Reading limits with this new release?
ESP32 mySQM+ Sky-Meter/Weather Station with loads of features
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Hi Robert,
I would like to know if this new release improves the SQM readings accuracy on very dark skies (21.5 to 22.00 range).
Thank you in advance.
the goal of getting accuracy in the 21.5 to 22 or above range is directly related to how much $$ you want to spend. Every design has comprimises.
Should this project be a little more accurate than the mysqmpro at the high end. yes. It does not suffer the compression issue of the tsl237 sensor at low light levels.
But honestly, unless you live in a really really really dark site its not worth chasing the higher sqm.
There are better reasons to go with this project than simply sqm values- ie, connectivity, cloud modelling
Ok, understood. Thank you.
The fact is that my second residence is about 21.5, and it is just next to an area were the LP decreases quickly, going as low as 21.8 relatively near from my location.
I would like to investigate if worth to imaging outside or not, and which would be the best place to go. I understand that I can figure what's the difference without having accurate absolute values, but my concern is if the previous project (that I recently posted on the used build topic) would have enough accuracy for relative values comparison, or I would need in any case to go to this new release.
At the higher end this esp32 release is much better.
But it is of cource uncalibrated unless you have access to some high end laser and optics gear.
But when you decided to jump into this project, make sure you will need a bigger project box. :) Things will get hot in there. I decided to mount to BME280 outside.
Even Unihedron in its FAQ states that SQM around 22 is the lowest it can detect and has not recorded values higher than 21.9 with its units.
As I have stated before relying on SQM readings to decide whether to image is a mistake. There is a lot more to consider.
see
https://sourceforge.net/p/arduinomysqmskyqualitymeter/discussion/general/thread/06b7673b06/?limit=25#a9db
and
https://sourceforge.net/p/arduinomysqmskyqualitymeter/discussion/general/thread/548caf3626/?limit=25#b514
Hi Robert,
Yes, I had read this topics, and I understand the general limitations for choosing a site to imaging, and for the fact that this is a DIY project. My concern was basically if I was going to hit a limit and so read the same value even driving deeper and deeper into the dark zone.
I suppose that the only way is to test it and see what happens.
Thank you.
Technically, this release should be able to measure sqm levels of 25.08355939
However, this depends upon on a lot of things about how well you can limit stray light affecting the sensor. [no led, no oled etc]
I mounted the TSL2591 with hot glue then spray it with Matt black paint. No light leak at all. :)
Last edit: TomAstro 2020-03-24
Hi,
sorry if I get back to this topic, is this new sensor better than TLS? Should I choose this new one. In case any brief details would be nice!
Thank you.
Cheers,
Giovanni.
Hi
It depends what you want to do and what you want to measure.
They are really two different sensors that are worlds apart. And the projects referred to are not same and again, are worlds apart.
The Unihedron and mySQMPRO use both the TLS237 sensor, which converts the light falling onto the sensor into a frequency which is proportional to the amount of light (irradience). The lower the frequency, the less the light (higher SQM reading).
In all the references and projects and discussion threads, I point out
1. Do not rely on a high sqm reading for imagining
2. Do not chase high sqm readings or become fixated by them
3. Any DIY project also has inherent flaws and assumptions.
If you want to be a memeber of the world "SQM" providing sqm readings, please do not waste time with these DIY projects. Go and get a Unihedron.
For the mySQM+ project, a TSL2591 sensor is used, which is a lux sensor that spans both visible and IR light. I have argued that this is more relevant to imaging because
1. IR is not seen by the eye
2. Most astro imaging camera's have good IR sensitivity.
The TSL237 sensor was not considered because they are getting more difficult to acquire,
The TSL2691 provides a lux reading from very high to very low levels. A loose conversion from LUX to "sqm" is acquired, but as pointed out in the pdf, is an approximation. The pdf also points out that fo not chase the dragon (trying to get lower and lower values) because there is a point of dimishing return, and to rely on a number of things for good imaging.
I am not a visual person - I do not need a device that emulates the eye, because that is not what I use to capture images, I use an astro camera, and most of the images I think about imaging have a reasonable IR component (nebulas). To do that I do rely on high altiude jet streams as well as low lux levels.
Regards
Robert