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Transparency impact on NV

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#1 GOLGO13

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Posted 27 July 2020 - 04:56 PM

One thing I've noticed is transparency plays a huge role in NV performance. I'm sure it also does for glass observing, but in light pollution every DSO is pretty faint in glass.

 

I don't appear to have great transparency too often but have had some really good nights here and there. Maybe it's something to do with the mountains here. When I lived in the St. Louis area, strong storms would blow through and we'd have some really clean and transparent skies. But here in WV the storms don't seem to be as strong and I think the mountains save us a bit. But also makes for not the best skies or even clear skies too often. 

 

This is an important thing to consider when evaluating NV performance. 

 

One of the objects I noticed this the most on was the Horse Head nebula. Some nights with NV it was barely visible, then the next night it's pretty decent. 

 

So on nights where transparency is no good I switch over to planetary and lunar observing.

 

A point here is don't judge things on one or two night's observing.



#2 Eddgie

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Posted 27 July 2020 - 05:19 PM

I am not sure about your location, but I know that the Smokey Mountains, not that far south of you, are thought to have gotten their name from the fact that the vegetation exhales volatile organic compounds that have a high vapor pressure.  In normal pressure and temps, these will form a smoky haze.

 

I have driven the Skyliine Drive and have noted that along the mountain chain, there appears to be a similar haze.

 

When the temps are cooler and there is a scrubbing wind, this haze can be swept off. I remember being on the Skyline drive on such a night about four years ago and I had my night vision gear.  The view from the Skyline drive was dramatic under those conditions.

 

And to your point, yes, this kind of atmospheric effect is pretty damaging. 

 

I suspect though that this is possibly an atmospheric condition that you might be living under. 



#3 nimitz69

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Posted 27 July 2020 - 06:44 PM

Humidity certainly has an effect. I remember shortly after getting my NVD and not being able to see all these nebula that everyone posted about I started to wonder about my tube. Turned out that with the humidity at 90% it was a struggle. Switch to 2 night ago and while my AP system was (finally) capturing some images of Neowise I started to just pan around with my NVD at 2x and I started to see what i thought at first were clouds (it was partly cloudy) but it turned out to be a bunch of nebula looking SE ... smile.gif

#4 Mike Lockwood

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Posted 27 July 2020 - 07:53 PM

What I find is that if it's mostly a transparency issue, NV usually has enough gain to usually offset the loss of light.  I'm still amazed at what I can see on a dark, hazy night, especially near fairly unpolluted areas of the horizon.  WSP comes to mind.

 

However, if there is something in the atmosphere that scatters light pollution, then performance will degrade due to that.



#5 Peregrinatum

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Posted 27 July 2020 - 10:01 PM

I have noticed this as well... seeing is no biggie, clouds, well you can see in between clouds of there is no constant cover... but transparency can impact the night with NV



#6 bobhen

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Posted 28 July 2020 - 07:35 AM

Moisture in the air exacerbates light pollution. The water droplets act like lenses scattering light. Snow cover also exacerbates light pollution, as the snow reflects more artificial light up into the sky. Both really hurt conventional deep sky observing.

 

But I have to say, even under those conditions, NV still impresses. I have some log notes from some god-awful humid nights here in PA, at my light-polluted location that is filled with impressive NV deep sky observations. I don’t think there has been one clear night, no matter how bad the transparency, that I have not been able to see the Horsehead Nebula, even when somewhat low on the horizon. And Philadelphia is definitely not the dry and dark southwest.

 

Of course some nights are just better than others but that is to be expected. But the detrimental impact of light pollution and humidity, although harmful, are nowhere near as harmful to NV as they are to regular observing.

 

Bob



#7 GeezerGazer

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Posted 01 August 2020 - 10:49 PM

Yep, transparency seems more important than seeing conditions for NV.  In CA, when we have wildfires and smoke covers the state, I just wait until it clears or I go far enough away that the smoke is not a problem.  When it's foggy here in winter, or even sometimes in summer when humidity is very high, it degrades NV.  Thankfully, these issues are not a constant irritation.  



#8 ManuelJ

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Posted 03 August 2020 - 05:35 AM

NV should be very affected by atmospheric water vapour content.



#9 bobhen

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Posted 03 August 2020 - 06:22 AM

NV should be very affected by atmospheric water vapour content.

NV is impacted by atmospheric water vapor but it is not as impacted as regular glass.

 

Water Vapor
Smoke
Light pollution

 

They all impact NV AND regular glass observing. But with NV you start with a stronger signal (more photons) received from the object that you are observing, and that is true whether the sky is pristine or not. And if filtration helps, then it will be many times more effective with NV than regular glass because you can use stronger filters and attain better contrast.

 

Bob


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#10 GOLGO13

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Posted 20 May 2021 - 06:16 PM

Don't want to completely sound like captain obvious here, but transparency is extremely important with NV. Recently we've had "clear" skies for about 4-5 nights, but only one of those nights was fairly transparent. If you try to use your NV scope with thin clouds or haze, it will not produce very good results. You may even think there is something wrong or NV doesn't produce good results.

 

One object I noticed this the most with is the Horse Head, Flame and that area. One night it will be barely visible, and the next night it's pretty bright.

 

This is something to consider when using NV and evaluating filters etc.

 

It almost seems sometimes it's more important than glass, but I'm sure it's the same...just more noticeable with NV because you can see more.


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#11 a__l

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Posted 20 May 2021 - 06:27 PM

Yes it is. The best galaxies I have seen only in a transparent sky.



#12 blackhaz

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Posted 20 May 2021 - 06:42 PM

Couldn't agree more. On transparent nights my 90 mm showed more than the 6". Kind of brings peace of mind - cools down the aperture fever a bit when you know you can see the "bottom" of this sky.



#13 DanDK

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Posted 21 May 2021 - 09:19 AM

I definitely notice the difference. I took these 2 phone pics of M101 on clear, moonless nights.  First one in April, on a cool night with good transparency, second in humid July.

Attached Thumbnails

  • M 101 -Pinwheel.jpg
  • M 101 27mm.jpg

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#14 GOLGO13

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Posted 21 May 2021 - 09:52 AM

Yep. It can be pretty dramatic a difference.



#15 blackhaz

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Posted 21 May 2021 - 12:16 PM

Dan, do you mind me asking what scope is that?


Edited by blackhaz, 21 May 2021 - 12:16 PM.

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#16 PEterW

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Posted 21 May 2021 - 01:15 PM

Have a few nebulae you are familiar with to check what the sky is like… so you know when it’s worth going after the fainter ones. North America, monkeyhead, pacman for instance.

PEter

#17 DanDK

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Posted 21 May 2021 - 06:11 PM

Dan, do you mind me asking what scope is that?

It's a 10" Orion dob (xt10g).  I believe I used a 27mm eyepiece with the monocular for both pics.


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#18 ButterFly

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Posted 21 May 2021 - 07:22 PM

I've seen gravity waves plenty of times with the device in otherwise clear skies.



#19 DanDK

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Posted 21 May 2021 - 09:53 PM

I've seen gravity waves plenty of times with the device in otherwise clear skies.

Sometimes, when I suspect that scattered clouds might be interfering with telescopic views, I take off the monocular, aim it up at the sky, and the clouds show up clear as day. I suppose they're just reflecting light pollution, but combined with the stars it makes for some pretty cool views.


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#20 cnoct

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Posted 22 May 2021 - 05:29 AM

There have been many times that poor transparency has had me doubting my equipment. When it's been real bad, confluence of volcanic aerosols, water molecules and natural airglow has caused me to believe my tubes were on the out. Transparency can make or break the views, transparency is hardly ever overstated for the importance it on NV astronomy.
 
This video of propagating airglow shows, in a rather dramatic way, just how impactful transparency can be to NV systems and/or lowlight cameras:  https://youtu.be/cc4zzoaPws0
 
That airglow in that video wan't visible to the naked eye and one would, if naked eye observing, have estimated the transparency to be rather high.

#21 bobhen

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Posted 22 May 2021 - 05:38 AM

Poor transparency, even with a clear sky, can certainly negatively impact observing. 

 

Even in my Bortle 9 sky, with good transparence, it’s remarkable what can be seen.

 

Dust and water droplets also magnify light pollution.

 

I think NV observers notice transparency more because intensifiers and filters do such a good job with light pollution that transparency, and how it negatively impacts observing, becomes more obvious.

 

Bob


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#22 ArsMachina

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Posted 22 May 2021 - 06:17 AM

https://www.cloudyni...y-impact-on-nv/



#23 GOLGO13

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Posted 22 May 2021 - 06:40 AM

https://www.cloudyni...y-impact-on-nv/


Guess I'm repeating myself Lol.
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#24 ButterFly

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Posted 22 May 2021 - 05:26 PM

Polarizers help darken the moonlit sky just as they do during the day.  It helps those clouds pop right out, for those so inclined.  I've tried polarizers with galaxies as well, during moonlight, and it's surprisingly close to what the 642 does, in some parts of the sky.



#25 Tyson M

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Posted 24 May 2021 - 02:54 PM

I merged the two topics now to consolidate the posts/experiences and keep this topic going.


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