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SQM advice

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#1 AstroLabs

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Posted 22 November 2019 - 06:39 PM

Any recommendations or advice on a good sky quality meter?

#2 TOMDEY

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Posted 22 November 2019 - 07:54 PM

Well, I sure like my Unihedron little pocket field model. It's the one that is directional... you point it at the part of the sky that you are looking at or imaging. It's footprint on the sky is still huge, so you get a good directional weighted integration that is good indicator of what you will be experiencing looking there. They also have a very wide field model and some fancier ones that display a lot of parametrics. Anyway, this one... you just point it and click the one and only button and wait for the beep (~3 - 10 seconds, typical, depending on how dark the sky is). Convenient and reliable. Take a few sequential readings; ignore the first one. Under dark skies, you will notice that the Milky Way is a lot brighter than the other parts of the sky --- as it should be, of course!  It's also inexpensive and rugged... battery lasts forever. My backyard sky typically comes in around 21.35.Tom

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#3 bmhjr

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Posted 22 November 2019 - 09:14 PM

+1 to what Tom says. I have used the same model for a few years now. Works great.  Original battery.



#4 Coconuts

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Posted 22 November 2019 - 09:17 PM

Unihedron also offers a small angle version (SQM-L; http://www.unihedron.../projects/sqm-l), which you can simply point at the zenith, and not worry about nearby encroaching forest or individual trees, the sides of your house, and such. From their FAQ:

 

What is the difference between the SQM and SQM-L?

  • Here (http://www.unihedron...ksky/comparison) is a chart showing the differences at a glance.
  • The main difference is the field of view. The SQM-L (with lens) is an improvement over the SQM. The lens collects more light from a smaller cone so that the meter is not affected from lights or shading on the horizon.
  • The SQM spec for field of view is located in this technical report. A comparison of the angular response for both meters is here. Generally speaking, the SQM-L 'Half Width Half Maximum' is ~10 degrees as opposed to ~42 degrees for the SQM.
  • The SQM-L is better suited for astronomy and dark sky enthusiasts. It has a lens to narrow the field of view so that street lights and buildings or trees do not affect the reading very much.
  • If you expect to always take readings at dark sky sites in an open field then the regular SQM will do fine for that task.

There is another SQM that may well be waiting a bit longer for.  That is the Astromechanics Light Pollution Meter Pro (https://astromechanics.org/lpm.html).  This has a number of features not found in the Unihedron SQM-L, and is priced a bit lower.  Both use the same IC, though (the remarkable Taos TSL237 fluence to frequency converter; https://ams.com/docu...156_3-00.pdf).  I placed a pre-order for the Astromechanics Light Pollution Meter Pro about four months ago, and when I asked about the status last month, Sergey replied:

 

"Now we are improving the procedure for calibrating the device and also compare it with SQM-L (we bought one unit).
We got some feedback from users. Typically, differences in measurements don't exceed 0.1-0.15 mag.
But one user reported us about the difference of 0.4 mag. It's a bad result. We have to check everything many times.
I will let you know when the device is ready for order".

 

So stay tuned!

 

All the best,

 

Kevin


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#5 Samir Kharusi

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Posted 23 November 2019 - 03:38 AM

Pssst. You do realize that any adjustable digital camera is also an excellent tool for measuring skyfog? Click here and go measure. Accurately. Tonight.



#6 Coconuts

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Posted 23 November 2019 - 07:30 AM

Samir:  I at least did, and your work back then was both impressive and valuable.  But shiny new toys!

 

All the best,

 

Kevin



#7 AstroLabs

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Posted 24 November 2019 - 08:13 AM

Many thanks. I will take a closer look. Sounds like a quality instrument.


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