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NV and M51 spiral arms?

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#1 MattJ

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Posted 20 January 2020 - 09:24 AM

I'm interested in hearing about observations of M51 and its spiral arms using NV visually.  Does NV help a lot?  What were your sky conditions, aperture, speed, magnification, and filters?  Thanks.  



#2 chemisted

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Posted 20 January 2020 - 09:38 AM

Spiral arms of face-on galaxies shine heavily in the blue end of the spectrum and, as such, are one of the deep sky objects that benefits the least from image intensifiers that really have very little boost below 500 nm.  In contrast edge-on galaxies get a wonderful boost due to the red light dominance imparted by dust in the galaxies.


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#3 highfnum

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Posted 20 January 2020 - 02:45 PM

it helps but not greatly 

here is f4.5 10 inch intens NV

with my S8 phone

m511229.jpg

 


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#4 Eddgie

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Posted 20 January 2020 - 03:26 PM

Well, I guess it is all relative.   From my home (red zone), I was never able to see any hint of spiral arms on M51 when using conventional gear.  Now, I can see them quite well in my 6" f/2.8 and in my 12"  I can see them better than I ever saw them under all but deep surburban skies. 

 

I constantely see galaxies in my 12" scope that I tried for decades to see using scopes as large as 14", and now from the same yard even after the increase in light pollution we have had over the last decade, I am seeing more galaxies than ever before.

 

Anyway, I though M51 was hugely improved over glass eyepieces though again, most of my observing has been from my light polluted home sky. 


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#5 bobhen

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Posted 21 January 2020 - 09:13 AM

Most galaxies are at extreme distance and don’t show any or much structure, even with 60-second exposures. The famous galaxies that do show arms and detail etc. still need multiple second exposures to show real fine structure and detail. Extremely large aperture (say 25” and up) used visually or NV used on telescopes half that size cannot compete with long exposure cameras.

 

Having said that, think of using NV as doubling your scope’s aperture. So, ask yourself, used visually (unassisted) will going from say a 6” telescope to a 12-inch telescope deliver what you want under your sky? Yes, the galaxies will be brighter, easier to spot, you will spot more galaxies and some will show hints of details in the larger scope compared to the smaller aperture. That is the boost you will get with NV but it won’t be close to the detail in a long exposure image.

 

As an example: Under my extremely light polluted sky, my 120mm and 8” telescopes with NV show more galaxy detail, easier to see detail and more galaxies than my old 15-inch Newtonian using just glass ever did. Even with the 15” Newtonian, I never saw galaxy 891. But with my “small” 120mm refractor and NV, I can now just pick up a faint 891. So yes NV will show more. But NV does not come close to the level of detail in 891 that my C11 and video camera showed with a 60 second exposure.

 

Bottom line: NV is better than visual on all galaxies and will “roughly” double the light gathering or aperture of your telescope. Will that be enough? But NV is not close to long exposure imaging for galaxy detail. So if that is what you want, that is the road you need to take.

 

Bob


Edited by bobhen, 21 January 2020 - 09:14 AM.

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#6 MattJ

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Posted 21 January 2020 - 12:32 PM

Thanks everyone for the replies.  HIghfnum, I think that view is pretty good!  Is it close to what you see visually?  Was this taken using the NV device at prime focus?  Could you see the spiral arms with your scope without using NV?  

 

Eddgie, I know your 6 inch scope is very fast, but do you think if I were using a 6 inch f/5 reflector or 102 mm f/5 achromat from a suburban site with NV, would I have a chance of seeing M51's spiral arms?  

 

Bobhen, thanks for the example with your scopes.  It's really helpful.  I don't think I'm interested in getting into video EAA.  I like the simplicity of NV.  



#7 highfnum

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Posted 21 January 2020 - 02:28 PM

its somewhat better than visual 

yes NV at prime focus F4.5

viual is more of a point surrounded by fuzzy



#8 slavicek

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Posted 21 January 2020 - 11:29 PM

Spiral arms of face-on galaxies shine heavily in the blue end of the spectrum and, as such, are one of the deep sky objects that benefits the least from image intensifiers that really have very little boost below 500 nm.  In contrast edge-on galaxies get a wonderful boost due to the red light dominance imparted by dust in the galaxies.

I second that. From my experience, so far, NV does not do improve much the views of galaxies. You'd be probably disappointed if you got the NVD just for galaxies. It's the nebulas where NV "rocks".



#9 Eddgie

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Posted 22 January 2020 - 10:16 AM

 

Eddgie, I know your 6 inch scope is very fast, but do you think if I were using a 6 inch f/5 reflector or 102 mm f/5 achromat from a suburban site with NV, would I have a chance of seeing M51's spiral arms?  

 

 

I can see them with a 180mm SLR lens. Heck I can see them at 3x. Now they are tiny tiny tiny, but I can see them. 

 

I can see them at f/5 with my 12" and the scale is a lot better than in the 6" though the arms are very subtle. 

So yeah, I think it would be pretty easy with a 4" f/5.  It will be small, but you should absolutely be able to see the arms from the burbs.  I live 4.5 miles from the center of the city and again, I can see them even with an SLR lens. 
 



#10 Jeff Morgan

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Posted 22 January 2020 - 11:32 AM

I second that. From my experience, so far, NV does not do improve much the views of galaxies. You'd be probably disappointed if you got the NVD just for galaxies. It's the nebulas where NV "rocks".

 

No doubt that nebula are top of the scale for performance, and that is a tough act to follow. The h-alpha line lies where the GaAs technology is very sensitive, and one can get a line filter to screen out the light pollution. In fact, most of the intra-galactic targets are great in NV.

 

Galaxy performance tends to be more nuanced:

 

  • NV is the best 27mm eyepiece you will ever turn on a galaxy.
  • Because galaxies are extended objects, any attempt to increase magnification slows the focal ratio and dims the view. OTOH it is very easy to pump up the magnification with a conventional eyepiece.
  • NV is less sensitive in blue, so spiral arms seen face on get a small boost (as they are not entirely blue), not a big boost like nebula.
  • Galaxies are continuous spectrum emitters, so there is improvement - but light pollution is also continuous spectrum so employing filters offers marginal gains, not the enormous gains of h-alpha.
  • Galaxy "red" features like cores and dust lanes, are well enhanced.
  • Irregulars and Ellipticals are much easier to see in NV, as are edge-on spirals. Despite light pollution, it does allow me to see galaxies from the 20.5 backyard that are invisible conventionally.

 

The toughest NV challenge is face-on spirals. My 27mm NVD easily beats my 27 Panoptic here - but I can switch to a Leica Zoom and go down to 9mm focal length with relatively no penalty. Can't do that with NV.

 

The ideal galaxy type for NV would be high surface brightness (to allow some room to barlow) and large angular size. M82 is a prime example, and it does take magnification very well in a NVD. But most galaxies are quite small, and low surface brightness. Easy to detect with NV, but going after detail is problematic.

 

Overall I would agree with Slavicek that if galaxies are the only thing you do (and there are people that fall into that narrow category), the $4K spent on NV would buy a lot of automobile depreciation to drive to dark skies.


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#11 highfnum

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Posted 23 January 2020 - 12:32 PM

the intens helps a little bit more than AsGs tubes 

subtle only 

here is some 81 82 shots-   look carefully you can see outer arms (barely) 

 

m8182.jpg

m8182b.jpg


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