Jump to content

  •  

CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.

Photo

Smaller 'scope WITH NV vs Larger without?

  • Please log in to reply
12 replies to this topic

#1 bigdobsonfan

bigdobsonfan

    Lift Off

  • -----
  • topic starter
  • Posts: 19
  • Joined: 31 May 2021

Posted 02 July 2021 - 08:26 AM

Ignoring for a moment the differences in everything else (better resolution, full bandwidth and use of filters/wider band sensors) is there some kind of rule of thumb about how much light gathering is gained by stacking Gen3 night vision to a telescope with a mid-sized lens vs just using a larger telescope?  I thought I had read once gaining 2 magnitude though I forget where so i'm using that.

 

Making my thinking public - so that people can point out if i'm wrong, if I follow that logic then if the limiting magnitude is 6 in a rural area for naked eye, I should be able to see 8 through the NV itself.  (the difference may be even more in an urban area - if I can only see 4 in an urban area, could I see more than 6 from the urban backyard?  I'd just heard NV was the ticket for urban viewing and wondered if it was more than just light gathering) 

 

So if I take even basic 50mm binoculars or telescope to the rural area if I believe some online charts https://twcac.org/Tu...itude_table.htm I might be able to see magnitude 11 rurally, and putting the NV behind it would mean seeing down to magnitude 13, almost comparable to a 5 inch telescope.  Is that about right?  Same chart, an 8 inch scope viewing magnitude 14 with NV (gaining 2) would be almost comparable to a 20 inch scope listing as magnitude 16...

 

I'm just referring to raw viewability of stars and deep space objects and the reason for my asking is to try to get some idea of how much larger a telescope would have to be to be remotely comparable for realtime viewing.  Ie - someone's 8 inch scope with an NV tube on the back letting me see what I might expect to see without the NV tube in a 20 inch scope.  Also potentially figuring out the sweet spot where paying $3000 for an NV tube costs less than 2.5x more aperture.  smile.gif


Edited by bigdobsonfan, 02 July 2021 - 08:28 AM.


#2 GOLGO13

GOLGO13

    Fly Me to the Moon

  • *****
  • Posts: 6,538
  • Joined: 05 Nov 2005
  • Loc: West Virginia

Posted 02 July 2021 - 10:05 AM

You know, it's a strange thing with NV. And this is kind of a hard question to answer. Very small scopes with NV can show way more then a larger telescope with glass in the same sky. My 50mm guide scope shows the flame and horsehead in my Bortle 6 skies.

 

What makes the comparisons hard though are the differences in focal length. I think Night Vision really benefits from having a variety of focal length setups. The device 1x is great but somewhat limited in use. Then something like a 50mm guide scope provides a nice wide field but a bit more zoomed in. Some sort of medium focal length 600-800mm is helpful and more zoomed in. Then I think it's really good to have something like a 8 inch SCT 2000 focal length for Globulars and small planetary nebulas.

 

While small scopes does well with NV, I do prefer some aperture. Some of that could just be getting the more focal length. 

 

Fast scopes are helpful for many situations (Nebulas). But I do find slow scopes are still useful for certain objects.

 

Here's my general thought of NV in light pollution compared to glass in a dark sky. NV in light pollution reminds me of glass in a very dark sky. I personally feel (though it's been a bit since I've been in a dark sky) that glass in a dark sky is better, but NV in light pollution is similar. Except, some objects would be tough in a dark sky with glass (Horsehead, flame, california, etc). But if you want a dark sky like feel (visual) in light pollution, NV is pretty good. It's got a very visual astronomy feel to me. I don't see it being astrophotography like (maybe the views of the Orion Nebula sometimes are pretty good). 

 

All this being said I've not used a 20 inch scope in light pollution. And I've only used my NV setup in light pollution. I understand it can work even better in darker skies. I'm looking forward to trying that sometime.

 

I think my general opinion is, if you can't get to dark skies NV is very good. However, it appears people do like using it in dark skies also. I don't think people should get rid of their glass eyepieces. It's a bit of a different view. I have better memories of objects in glass than NV. But again, I've not used it in dark skies. I think unless you are in extremely dark skies, NV probably is better. Based on what I've surmised from other folks' comments here. 

 

Obviously it's not good for seeing color in stars, planets, moon, etc. Which is kind of funny thinking about that now because my favorite objects are the Sun, Moon, Planets...though I do like Globulars a lot.


  • Sarkikos, 1E1HFPPE, Dale Eason and 4 others like this

#3 JMW

JMW

    Aurora

  • -----
  • Posts: 4,577
  • Joined: 11 Feb 2007
  • Loc: Nevada

Posted 02 July 2021 - 10:50 AM

I have been happy with my PVS14 on my SVR90T for home grab and go or on my 8 inch f/6 newtonian as one of two travel scopes with our Arctic Fox 22G trailer. We also bring a TEC140ED for the other visual setup. Under dark skies we enjoy the brighter stuff with eyepieces and the lowest contrast or Ha stuff with the PVS14. The ease of the 8 inch Dob setup and the added abilities of the PVS14 keeps me satisfied

 

I own a 14.5 inch Webster dob but I find I don't have room for it when bringing my imaging rig plus a couple of visual setups. I am keeping the larger dob with the hope to move to a darker location with an acre of land so I can appreciate the bigger dob at a rural home under open dark skies after retirement.


  • bigdobsonfan likes this

#4 chemisted

chemisted

    Viking 1

  • -----
  • Posts: 582
  • Joined: 24 Feb 2012

Posted 02 July 2021 - 01:17 PM

Ignoring for a moment the differences in everything else (better resolution, full bandwidth and use of filters/wider band sensors) is there some kind of rule of thumb about how much light gathering is gained by stacking Gen3 night vision to a telescope with a mid-sized lens vs just using a larger telescope?  I thought I had read once gaining 2 magnitude though I forget where so i'm using that.

 

Making my thinking public - so that people can point out if i'm wrong, if I follow that logic then if the limiting magnitude is 6 in a rural area for naked eye, I should be able to see 8 through the NV itself.  (the difference may be even more in an urban area - if I can only see 4 in an urban area, could I see more than 6 from the urban backyard?  I'd just heard NV was the ticket for urban viewing and wondered if it was more than just light gathering) 

 

So if I take even basic 50mm binoculars or telescope to the rural area if I believe some online charts https://twcac.org/Tu...itude_table.htm I might be able to see magnitude 11 rurally, and putting the NV behind it would mean seeing down to magnitude 13, almost comparable to a 5 inch telescope.  Is that about right?  Same chart, an 8 inch scope viewing magnitude 14 with NV (gaining 2) would be almost comparable to a 20 inch scope listing as magnitude 16...

 

I'm just referring to raw viewability of stars and deep space objects and the reason for my asking is to try to get some idea of how much larger a telescope would have to be to be remotely comparable for realtime viewing.  Ie - someone's 8 inch scope with an NV tube on the back letting me see what I might expect to see without the NV tube in a 20 inch scope.  Also potentially figuring out the sweet spot where paying $3000 for an NV tube costs less than 2.5x more aperture.  smile.gif

Dennis di Cicco answered your question when he reviewed the TV/TNVC PVS-14 device in the June, 2018 issue of Sky and Telescope (p.58).  Todays Gen 3 tubes available to amateurs provide a 3 magnitude benefit.  Dennis did a good job of providing the details of his evaluation.


  • Sarkikos, Dale Eason, Tyson M and 1 other like this

#5 bobhen

bobhen

    Fly Me to the Moon

  • *****
  • Posts: 5,388
  • Joined: 25 Jun 2005

Posted 02 July 2021 - 02:16 PM

Magnitude is not the only criterion.

 

Yes you will go deeper with an intensifier but there are objects that are difficult or impossible to observer in a very dark sky and with large aperture that can be seen with NV, even in heavy pollution.

 

WHY?...

 

…Because for many deep sky objects “contrast” is as "or even more important" than aperture.

 

Because of an intensifier’s extreme light boost, one can add filters to an intensifier that are so strong they can only be used for CCD imaging – and NOT for visual, no matter how large your scope is.

 

The combination of much more light than even a large mirror delivers, coupled with extremely strong filtration delivers such high contrast that when using an intensifier one can observe targets that are considered CCD imaging targets only.

 

If you go to an extremely dark site you “might” be able to glimpse  Barnard’s Loop or the Horsehead and other such targets but with great difficulty and certainly with more difficulty and in less detail than when using an intensifier. Other targets will not be observable without the light boost and contrast enhancement of an intensifier.

 

In light pollution it’s no contest. There’s just not enough contrast for visual, even for large mirrors. With an intensifier, those same deep sky CCD-only targets are readily available, even in "extreme" light pollution. 

 

Bob


  • Starman81, Dale Eason, ArsMachina and 4 others like this

#6 Jeff Morgan

Jeff Morgan

    Voyager 1

  • *****
  • Posts: 13,439
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 02 July 2021 - 03:30 PM

I'm just referring to raw viewability of stars and deep space objects and the reason for my asking is to try to get some idea of how much larger a telescope would have to be to be remotely comparable for realtime viewing.  Ie - someone's 8 inch scope with an NV tube on the back letting me see what I might expect to see without the NV tube in a 20 inch scope.  Also potentially figuring out the sweet spot where paying $3000 for an NV tube costs less than 2.5x more aperture.  smile.gif

 

General rule of thumb I have experienced - NV is an "aperture doubler". And that is probably a bit conservative overall. 

 

If you are using that as justification to stick with a smaller scope I would say "don't".

 

Base your scope size considerations on what you can afford, what you can transport, and what you can physically handle.

 

Ideally, you want to get to a point where you have more the one scope to use with NV, not just a single scope. NV really flips the old paradigm of "one scope many eyepieces".

 

If the decision is "I have "x" dollars to spend right now", then I would say get the NV first because of the versatility. Then come back and get the large scope next year. But that's just me. And good arguments could be made the other way too. 


  • Sarkikos, Starman81, 1E1HFPPE and 8 others like this

#7 nimitz69

nimitz69

    Mercury-Atlas

  • *****
  • Posts: 2,819
  • Joined: 21 Apr 2017
  • Loc: A barrier island 18 miles south of Cocoa Beach

Posted 02 July 2021 - 05:09 PM

bobhen hit the nail on the head ... because of the extreme light intensification of an NVD you can use filters that only used to work when imaging. This allows you to see objects that used to be only well seen by the astro photo crowd.  Even a 20” visual scope can’t use these filters so you don’t get to se those objects. I’ve “seen” all sorts of things with my 81mm aperture AP setup that I can’t see with my 14” visual scope


  • 1E1HFPPE and Old Speckled Hen like this

#8 ButterFly

ButterFly

    Vanguard

  • *****
  • Posts: 2,388
  • Joined: 07 Sep 2018

Posted 02 July 2021 - 08:07 PM

Three very important things to keep in mind:

1) Seeing what you could not otherwise see is an improvement by a factor of infinity - thus incomparable;

2) At twice the wavelength, Airy disks (and thus PSFs) are twice as big, yielding half the resolution; and,

3) Magnitudes in near-IR do not need to correspond to magnitudes in the visual band.

 

Nonetheless, as rules of thumb, I have noticed:

For point sources, it acts like a scope of twice the aperture with respect to reach;

For extended objects, it acts like a scope of half the aperture - on crack!

 

For reference, here is what scope crack looks like when it has a Paracorr position:

 

67PP with Filter Wheel.png

 

All other forms of crack remain whack.


  • bigdobsonfan likes this

#9 rexowner

rexowner

    Viking 1

  • *****
  • Posts: 597
  • Joined: 13 Aug 2017
  • Loc: SF Bay Area, California

Posted 02 July 2021 - 10:06 PM

Can´t quantify this at the moment.   FWIW, an example.

 

In my skies, through 4" and 5" refractors, M13 and M4 are smudges that it takes some skill to identify.

Through a PVS-14, many individual stars are clear and they both are obviously globulars.

 

Basically, can see fainter objects that are otherwise just barely visible.



#10 bigdobsonfan

bigdobsonfan

    Lift Off

  • -----
  • topic starter
  • Posts: 19
  • Joined: 31 May 2021

Posted 11 July 2021 - 05:06 PM

Wow, I learned or verified something from every single post here, I guess i'm in the right place.

 

GOLGO13 - i'm baffled at how a smaller aperture could show more, could anyone else comment on this about what principle or physics might be operating here?  Could you explain more of what you feel so I could understand, like is it 'too much light gain' so something is blown out on the sensor or what does the difference look like?

 

JMW - Portability is an issue for me too, i'd love nothing more than to build a huge 20-30 inch Dobsonian, even if I do that project wont happen for years.

 

bobhen - thank you VERY much for that comment, I assumed that in all cases Gen3 NV would be 'something less' than a larger aperture, if it literally allows seeing things not otherwise possible that's a tick back in favor of earlier Gen3.  I might miss some things not having a huge telescope but I can see others - a fair trade off.  Are there things which can be seen through Gen3 that CCD does not though?  I don't suppose there's any kind of stacking Gen3 in front of a CCD is there, or is an astro CCD the 'image everything' holy grail for all digital viewing goals?

 

If stacking basically doubles aperture though a 10-15 inch with a Gen3 should give similar light gathering at least for those very dark objects - except those that for optics and physics reasons it cannot of course.  I'm aware I might gain similar (or even better?) images with a CCD imager (separate topic) but the Gen3 has more than one use including some unrelated film/video production type projects i've wanted to do for a long time where just using the real thing is likely easier than trying to fake the look with video processing.  (unless someone happens to know of a winning set of lighting techniques and Premiere processing to make it look very very accurate)


  • 1E1HFPPE likes this

#11 GeezerGazer

GeezerGazer

    Apollo

  • *****
  • Posts: 1,387
  • Joined: 06 Jan 2005
  • Loc: Modesto, CA

Posted 11 July 2021 - 06:36 PM

Hi Big, welcome to CN in general and especially to the NV forum!  Yes, you are in the right place.  waytogo.gif

You already have some great answers to your question.  

 

FYI, when you open the forum topics page, scroll down from the top and visit the BEST of NV page.  It lists several categories of information about NV.  Click on one of the subjects that interests you and you will get a page of links to past threads that you might find of interest.   They will keep you up all night when you can't observe.  lol.gif  The BEST of NV can answer a ton of questions you will have.  

 

If you are thinking about CCD as well as NV, then you are not opposed to imaging.  There is an NV Photography link that might interest you.  Several of us do NV Phonetography... so if you have a smartphone, you are in business.  You can find NV images in personal galleries like this: https://www.cloudyni...-phonetography/

Or, just go to the very first link at the top of the NV forum page which is a gallery of NV images.  

 

The question you ask in your first post has been asked many times by others wondering if NV is right for them.  Without question, the best way to find out is to try it.  It might be helpful to identify your location and ask if anyone with an NVD is close enough for a demo.  Good luck.

Ray


  • Old Speckled Hen and bigdobsonfan like this

#12 Old Speckled Hen

Old Speckled Hen

    Viking 1

  • -----
  • Posts: 593
  • Joined: 18 May 2020
  • Loc: 56.4451° N, 3.1670° W

Posted 19 July 2021 - 03:24 PM

Quote  "Wow, I learned or verified something from every single post here, I guess i'm in the right place."

 

Seconded, this has REALLY fired up my enthusiasm, esp from my light polluted domestic location.



#13 Jeff Morgan

Jeff Morgan

    Voyager 1

  • *****
  • Posts: 13,439
  • Joined: 28 Sep 2003
  • Loc: Prescott, AZ

Posted 19 July 2021 - 11:14 PM

For a time one of out local markets had Old Speckled Hen. A very nice ale, not sure if it was the original though.




CNers have asked about a donation box for Cloudy Nights over the years, so here you go. Donation is not required by any means, so please enjoy your stay.


Recent Topics






Cloudy Nights LLC
Cloudy Nights Sponsor: Astronomics