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Old 18-02-2018, 01:28 PM
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Dark Sky comparison from Tamleugh

Hope this is in the right forum, imho this is the most important equipment of all!

Just in case you were wondering whether dark skies were beneficial for even narrowband imaging...

https://youtu.be/e6eReQVXi4k
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Old 18-02-2018, 02:15 PM
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Not sure that the stretching has been adjusted to make a fair comparison, Simon? The stars in the dark sky image are quite a bit larger and my guess is that it's mainly due to a bigger stretch.

Just playing devil's advocate I would expect better results, of course.

Cheers,
Rick.
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Old 18-02-2018, 03:02 PM
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Thats ok rick. I'll triple check later, but when we reviewed the subs together the tamleugh subs did indeed have larger stars due to the wind gusts that night. So the night after that was dead-still, would have shown even greater differences
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Old 18-02-2018, 03:13 PM
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Thanks, Simon.
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Old 18-02-2018, 03:16 PM
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There is a stark difference between the two. Thank you Simon for sharing. Darker skies will surely allow for capturing fainter bits more quickly.

Speaking of dark skies, I'm really curious and itching to get my gear out at our new much darker location, comparing to Paddington at least. In spite of four! nearby street lights, I can easily see (without a telescope) Magellanic Clouds, MW and some features within the MW - huge improvement over yellow city night sky I have been accustomed to. I need to wait patiently for a drier weather though.
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Old 18-02-2018, 05:08 PM
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Ooh that does sound promising Slawomir, if you can see the 'clouds' thatll be a good improvement in contrast
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Old 18-02-2018, 07:47 PM
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Seeing and transparency have not been quantified here.

With a 5nm (or less) bandpass filter, even with a full moon, I have been challenged to find any benefit in a dark site.

Sorry...I don't agree that the sample data of two, as shown here, is a definite proof.
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Old 18-02-2018, 09:05 PM
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Getting some more samples soon Peter. Not sure if seeing would make much difference? The suburban subs had much better fwhm. Maybe others can chime in. Not sure of any other similar tests before, esp with exactly the same equipment.
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Old 18-02-2018, 10:03 PM
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Quote:
Originally Posted by SimmoW View Post
Getting some more samples soon Peter. Not sure if seeing would make much difference? The suburban subs had much better fwhm. Maybe others can chime in. Not sure of any other similar tests before, esp with exactly the same equipment.
Seeing is king.

Fainter stars and nebulosity are patently visible on nights of good seeing and transparency.

The narrower bandpass, the less the effect of skyglow. (this is why sub-angstrom Solar filters work so well)

What bandpass are you using? (not stated in the video)

I'd expect to see a minor difference at say, 12nm, but not at 5nm or 3nm
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Old 19-02-2018, 05:48 AM
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I used to observe a significant drop in background ADU in Paddington as the city was slowly going to sleep. Also, when there was a game on in nearby stadium, SNR would really suffer, not to mention neighbours turning lights on. That was with 3nm Astrodons. Moon of course had a significant impact too.

I’m yet to take my rig out at the new location, but I would be really surprised if I won’t be picking up fainter nebulosities much quicker, as the skies here are quite dark.

Apart from the amount of sky glow, seeing of course also play a key role but I think Simon’s compo was focused on illustrating of the former.

In any case, stars are bloated in the image taken at the darker site, so seeing was probably worse over there on that night, which wouldn’t help the data, yet clearly more nebulosity is visible.

My 2 cents.
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Old 19-02-2018, 07:01 AM
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Thanks for the further 'evidence' Slawomir. Yes its the contrast and adu value increasesi was trying to illustrate.

Peter, i'll add more into the video.they were 3nm Astrodons.

Maybe you could sponsor a full dark sky comparison study? 2 exactly matchind sets of Officina Stellare RH300 scopes and MX+ mounts with full frame FLI cameras. Happy to host!
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Old 19-02-2018, 08:11 AM
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Simon, shouldn't you be getting ADU value decreases at the dark site? That's the benefit... no additive light pollution. The decrease will be most pronounced in the background areas, of course, leading to the increase in contrast that you mentioned. That's why I think the video is misleading. The dark site data shouldn't look brighter (for a fair comparison) but it should look most contrasty.

Cheers,
Rick.
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Old 19-02-2018, 09:28 AM
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My bad rick, i meant a relative increase in the target adu signal.

The screen recording software, then youtube then fb all change the final video exposures! You should have seen how many different screen recorders i had to try before settling on the least invasive.

I will load up the original fits files soon for pure blinking comparison
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Old 19-02-2018, 09:57 AM
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Quote:
Originally Posted by SimmoW View Post
My bad rick, i meant a relative increase in the target adu signal.

The screen recording software, then youtube then fb all change the final video exposures! You should have seen how many different screen recorders i had to try before settling on the least invasive.

I will load up the original fits files soon for pure blinking comparison
If you have a few calibrated FITS files I'd be happy to run some stats for you.
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Old 19-02-2018, 10:00 AM
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Thanks Rick. For now all I have is Uri's best raw Ha subs, link here:

https://drive.google.com/open?id=1HR...rGJN-fvHOmB9kn
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  #16  
Old 19-02-2018, 04:25 PM
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oh and the comparison files and video is OIII, not Ha. Sh308 bubble is predominant in OIII. And most susceptible to light pollution from what I hear.
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