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First Galaxy Season with NV

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#26 Eddgie

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Posted 30 July 2020 - 12:09 PM

On bortle 2-3 that gain does not exist. I'm not using IR filters, maybe that's the problem.

You are expecting something that isn't logical.

 

If your skies are already dark enough to see something, then NV is not going to suddenly change it to something else.

 

If your conditions and equipment is such that you can already see the spiral arms of the Whirlpool galaxy, NV can make it a bit brighter, but it is not going to suddenly reveal things that are not there to begin with.

 

In my estimate, under dark skies, NV will give about double the aperture in benefit.  Now you can already see M51 from very dark skies with a 4" scope, so seeing it with NV is only going to be maybe the equivalent of seeing it with an 8" scope. Yes, it will be a bit brighter, but it isn't going to suddenly look like a 2 hour image capture.

 

I use the example of the telescope observations in the Deep Sky Observer's Guide.   They will often give an eyepiece impression of a subject from different size telescopes so that an observer can consider what they might be able to see under excellent conditions.  Here are the impressions for M100 from two different size scopes.

 

 

4/6" Scopes-75: Messier 100 is considerably bright in small telescopes.  Its elliptical halon elongated 4' x 3' ESE-WNW, and its core quite luminous, small, and round.

 

8/10" Scops-100x:  Messier 100 has a bright, small core embedded in a 5' x 4' ESE-WNW oval halo  The halo is generally smooth and its edges diffuse, but some variations in brightness  can e seen near the center of the core

 

12/14" Scopes- 135x: This is a fine, face on galaxy with a 6' x 5' ESE-WNW  halo surrounding a bright core....................................

 

The point here is that all three telescopes can already see M100 but what happens is that as the aperture is increased, the extension generally increases slightly and things are a little brighter.

 

And this is all you should expect from NV.  If you can already see it, then the best NV will typically do is to show it with a bit more extension or perhaps a bit brighter and with a bit more structure, similar to they way going from the 4" scope to the 8" scope does. 

 

If you are already seeing a galaxy as large as the catalogs generally list it, then what else would one expect from night vision.  If I can see the full extension in a given scope, then NV can't make it bigger than it is.

 

My own experience is that NV will give an increase in galaxy extension (if the galaxy is not already seen at full extension) equivalent to what one would get using conventional telescopes with double the aperture.  If you can see it, you can see it, but now the question is how much of the faint extension will you see with glass vs image intensifier.

 

So, the reason why NV does not produce the same result under dark sky as it does under lighter skies is that you are already seeing much of the galaxy, so there is not nearly as much room for improvement as with galaxies under brighter skies, where the long pass filter reduces light pollution allowing the galaxies to be seen they way it would appear from much darker skies.  


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#27 ManuelJ

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Posted 30 July 2020 - 03:30 PM

You are expecting something that isn't logical.

 

If your skies are already dark enough to see something, then NV is not going to suddenly change it to something else.

 

If your conditions and equipment is such that you can already see the spiral arms of the Whirlpool galaxy, NV can make it a bit brighter, but it is not going to suddenly reveal things that are not there to begin with.

 

In my estimate, under dark skies, NV will give about double the aperture in benefit.  Now you can already see M51 from very dark skies with a 4" scope, so seeing it with NV is only going to be maybe the equivalent of seeing it with an 8" scope. Yes, it will be a bit brighter, but it isn't going to suddenly look like a 2 hour image capture.

 

I use the example of the telescope observations in the Deep Sky Observer's Guide.   They will often give an eyepiece impression of a subject from different size telescopes so that an observer can consider what they might be able to see under excellent conditions.  Here are the impressions for M100 from two different size scopes.

 

 

The point here is that all three telescopes can already see M100 but what happens is that as the aperture is increased, the extension generally increases slightly and things are a little brighter.

 

And this is all you should expect from NV.  If you can already see it, then the best NV will typically do is to show it with a bit more extension or perhaps a bit brighter and with a bit more structure, similar to they way going from the 4" scope to the 8" scope does. 

 

If you are already seeing a galaxy as large as the catalogs generally list it, then what else would one expect from night vision.  If I can see the full extension in a given scope, then NV can't make it bigger than it is.

 

My own experience is that NV will give an increase in galaxy extension (if the galaxy is not already seen at full extension) equivalent to what one would get using conventional telescopes with double the aperture.  If you can see it, you can see it, but now the question is how much of the faint extension will you see with glass vs image intensifier.

 

So, the reason why NV does not produce the same result under dark sky as it does under lighter skies is that you are already seeing much of the galaxy, so there is not nearly as much room for improvement as with galaxies under brighter skies, where the long pass filter reduces light pollution allowing the galaxies to be seen they way it would appear from much darker skies.  

 

I have been observing quite a long time, and I'm still "young", so my eyes are still fit, let's say.

 

I'm saying that NV decreases extension on galaxies, makes some parts of the galaxy to just dissapear into the background. And this is not just my impression. Another person thinks exactly the same. We were observing M51 with a 20", and he said: "hhhmmm, looks like if we where observing the galaxy with a 10 inch".

 

I didn't believe him, and switched back to conventional eyepiece. And the galaxy went to full extension, although the dark lanes and spiral arms were less detailed.

 

I'm sorry if this hurts somebody, but the eye is still better in some situations than NV. At least on dark skies and non aged eyes.


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#28 The Ardent

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Posted 30 July 2020 - 03:32 PM

Dan
This was my 18” .

I find that using NV is like observing visually from a dark site +/- .

Galaxies have individual varying response to NV. In general from the city, NV allows direct observation of gx’s compared to averted vision visual.

From a dark site it allows observation of galaxies that may be impossible otherwise.

The higher the surface brightness, the better results with NV. A good example is M81 and 82.

Galaxies with a dust lane like M64, NGC 891 and 4565 are especially rewarding by the contrast of the dark lane vs Galaxy body.

In the city, the H-alpha regions of M33 are visible with H-a filter. They are not widely reported by visual observers with OIII.

My usual procedure is observe visually , and only use NV if unsuccessful. I have found that of the UGC galaxies , some respond well to NV, some don’t, despite similar listed magnitude.


[quote name="DanDK" post="10378133"]
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