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BobinKy
scholastic sledgehammer
Reged: 04/27/07
Posts: 930
Loc: Country road
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Which binoculars do better under light polluted skies, say NELM 4.5 and less?
How do the various specs contribute toward observing under bright skies? For example, magnification, aperture, FOV, exit pupil, eye relief, etc.
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Bob
38° Kentucky, USA
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EdZ
Professor EdZ
Reged: 02/15/02
Posts: 12516
Loc: Cumberland, R I , USA42N71.4W
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an ages old endless debate.
See the Best of threads for exit pupil threads.
edz
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Teach a kid something today. The feeling you'll get is one of life's greatest rewards.
member#21
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Mark9473
Carpal Tunnel
Reged: 07/21/05
Posts: 2664
Loc: 51°N 4°E
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My personal take on this is the following:
- for a given magnification, a large exit pupil (say 7 mm) gives a more pleasing image than a smaller one (say 5 mm) except in the very poorest skies (NELM 3 and below).
- you see more at higher magnification.
Therefore the buying decision is essentially about matching the following contradictory requirements:
- choose the magnification, then go for the largest objectives you can find, but:
- keep it compact, light, hand-holdable, affordable.
The optimum choice in the end is very personal.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63
WO Megrez II 80 FD + Baader 90° T2 Amici
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Rich N
Post Laureate
Reged: 09/22/04
Posts: 5303
Loc: San Francisco Bay Area, Calif...
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Most of the time I'm in light polluted skies. I often use 8x42s, 12x50s, a 15x50.
Rich
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ronharper
scholastic sledgehammer
Reged: 02/14/06
Posts: 989
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Under light polluted conditions, smaller exit pupils give the "illusion" of blacker sky. A lot of people go for this, and I like it too, because it is awfully pretty. But, in my experience, at a given magnification, you will see the most with an exit pupil that fills your eye. And that is pretty, too.
Ron
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Rich N
Post Laureate
Reged: 09/22/04
Posts: 5303
Loc: San Francisco Bay Area, Calif...
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Ron, it would be interesting to know how large your dark adapted pupils get under light polluted skies.
Rich
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Tony Flanders
Carpal Tunnel
Reged: 05/18/06
Posts: 2062
Loc: Cambridge, MA, USA
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Quote:
Which binoculars do better under light polluted skies, say NELM 4.5 and less?
As far as I'm concerned, the presence or absence of light pollution has little or no effect on the choice of binoculars and/or telescopes. If instrument A works better than B under dark skies, it will do so under bright skies too, and vice versa.
This may be different for people whose pupils open wider under dark skies -- if such people do in fact exist. As far as I can tell, my pupils open every bit as wide at my city sites as they do under pristine skies. But since it's impossible to measure this better than +-.05 mm, I can't state that categorically.
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Tony Flanders
eyeglasses
6x15 and 8x32 monoculars
8x25, 7x35, 10x30 IS, 10x50, and 15x70 binoculars
70mm and 100mm achromatic refractors
4.5", 7", and 12.5" Dobs
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ronharper
scholastic sledgehammer
Reged: 02/14/06
Posts: 989
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Rich,
I have tried to measure my dark adapted pupils, without much satisfaction. I have wanted to air some of these concerns anyway, and your question presents an opportunity.
In a darkened room, looking at my eye's reflection with a ruler, there are the concerns that
1) Is it dark enough, if you can see mm scale markings?
2) The eye must rotate in its socket to view the scale readings at the two edges of the pupil. This introduces an error.
I also made a tapered vision obstructor with a sliding slit so that I could move the slit to the widest part of the taper at which I could see a point source around both sides. This has the concerns:
1) The crucial observation is made through vanishingly small arcs at the edges of the pupil, so it is light-starved. The source needs to be quite bright, probably brighter than any star, possibly so bright as to decrease the pupil diameter.
2) Diffraction effects allow one to see around an edge at an angle beyond direct line of sight. Since the view in the limiting observation is so poor, I'm not sure I could distinguish diffracted light from direct.
Something about pupil size can also be learned from real life observations. If my eyes are 6.0mm, I'm only getting 42mm of good out of my 7x50. My 8x42 does indeed show the sky a bit darker, which is to be expected since my eyes are definitely bigger than its 5.2mm output. I'd expect the 8x42 to show slightly dimmer stars, due to putting the same light in the star images, but displayed against a darker background. Of course 8x should win any fine resolving contest with a 7x. These expectations are just what I see.
Misgivings and crudenesses aside, these methods give about 6.2 +/- 0.3mm. I think a closeup camera with a flash would be the ideal measurement, but don't have that capability.
As far as a the pupil's opening being sensitive to moderate degrees of light pollution level, I doubt it, as does Tony. I'm just not so sure about my dimly lit bathroom, or staring directly into streetlights.
For all this rant, it's mainly a fun thing for geeks to do on the notorious Cloudy Night, and would be a terrible thing to get hung up about. Whatever your eye pupils may measure, dare to dream! Django Reinhart only had two fingers on his left hand.
Ron
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Mr. Bill
Carpal Tunnel
Reged: 02/09/05
Posts: 2748
Loc: Just passing through.....
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It's easy to directly view the size of the dilated pupil under real observing conditions by determining whether your pupil is vignetting a selected eyepiece's exit pupil.
Using a telescope and an eyepiece of known exit pupil of say 5mm, choose a moderately bright star (not too bright or it will affect the results) and defocus it until you have a disk about the size of a quarter at arm's length.
Now move your eye in a circular motion looking at the disk edge. If it the extends out further as you do this, than the edge viewed when looking at the center is your pupil edge; you're vignetting the light cone.
If you can move your eye circularly and still see the defocused image without cutting off the edge, your pupil is larger.
Another hint that your pupil is vignetting the defocused image is that the edge will not be perfectly round as it should be if you are looking at the edge of the objective light cone.
I found using this method that my dilated eye under observing conditions is slightly larger than the exit pupil formed using a 26mm Nagler in an f/5 system. That is, about 5.2mm.
So this tells me that in an f/5 system, I am fully using the available light with a 26mm ep, but would be wasting light with a 32mm ep.
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10x50 Fujinon FMT-SX binos
15x70 AP binos + Paragon p-mount
Oberwerk 100BT 45 degree + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/6.5 Antares achromat
150mm f/8 homemade achromat....EE Barnard MW Sweeper
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery split tube
35mm Pan, 26mm Nagler, 17mm Nagler, 13mm Ethos, 8mm Ethos
Member IDA
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Markus
Postmaster
Reged: 12/26/04
Posts: 5385
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All of this seems to be nit picking. Do you see how RIDICULOUS this is?  Just imagine going up to a site where there are people observing and having a bit of fun and there you are next to your telescope with a ruler, a special light, and a clipboard writing down a bunch of useless data so you can determine how big your pupil gets.  Just enjoy the night sky with your toys !!! 
Any binocular, so long as it isn't some cheap thing with plastic lenses in it will make someone happy under light polluted skies or dark skies. 
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25X100 Skymasters
15X70 Skymasters
Home built Parallelogram Mount
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Mr. Bill
Carpal Tunnel
Reged: 02/09/05
Posts: 2748
Loc: Just passing through.....
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Well Markus...
I guess you just showed how irrelevant this thread (and for that matter this forum) is....
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10x50 Fujinon FMT-SX binos
15x70 AP binos + Paragon p-mount
Oberwerk 100BT 45 degree + Hercules fork mount
120mm f/5 Orion achromat + Moonlite focuser
140mm f/5.7 Vixen NeoAchro Petzvel refractor
150mm f/6.5 Antares achromat
150mm f/8 homemade achromat....EE Barnard MW Sweeper
8 inch newt with f/5 Swayze mirror
10 inch f/4.7 Orion newt + Paracorr
15 inch f/5 Discovery split tube
35mm Pan, 26mm Nagler, 17mm Nagler, 13mm Ethos, 8mm Ethos
Member IDA
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Bob:
For hand holding, get the largest magnification and aperture you're comfortable with. Typically, 10x50s are a good choice. 12x is a bit much for hand holding without Image Stabilization.
If you're going for premium binos, you'll find the apertures will more frequently be 42 mm, 10x42, for example. The reason for this is that premium binos are optimized for daylight use because the big market is hunters, racing enthusiasts, and birders and a 5mm exit pupil typically wastes aperture because pupils are normally smaller than 5mm, even in morning and evening twilight. As a result, 10x50s don't look any brighter in daylight than 10x42s while being heavier and more expensive to build with premium optics.
The magnification is more critical than aperture, so a 10x42mm premium binocular is a reasonable choice over a lower quality 10x50.
8x is a little low for light polluted skies. Binos under 42mm in aperture aren't the best choice for astronomy.
If you plan to use a tripod, the same basic rule applies -- more magnification and aperture are better, with magnification being more critical. The problem is that quality optics become extremely expensive in larger binoculars (which are highly specialized instruments). Most of the larger binos available represent considerable optical trade-offs to keep the price down.
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Quote:
All of this seems to be nit picking. Do you see how RIDICULOUS this is?
Markus:
Lots of analysis paralysis around here, I must say.  I don't think ANY bino that isn't some cheap plastic thing is great for astronomy, but some basic information will get most people where they want to go.
FAR more attention and concern seems to be devoted to choosing binoculars than using them... 
(And the behavior isn't limited to the bino forum.)
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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ronharper
scholastic sledgehammer
Reged: 02/14/06
Posts: 989
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Bob is a hardened bino forum member, and as such hardly deserves a straight answer. Anyway, it was a kind of complicated question.
Ron
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Ron:
The question was simple. It was the answers that got complicated. (Markus' point.)
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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Markus
Postmaster
Reged: 12/26/04
Posts: 5385
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Quote:
Ron:
The question was simple. It was the answers that got complicated. (Markus' point.)
Correct. The question is a formidable one, the answers were getting hairy, that's all. 
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25X100 Skymasters
15X70 Skymasters
Home built Parallelogram Mount
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ronharper
scholastic sledgehammer
Reged: 02/14/06
Posts: 989
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"Which binoculars do better under light polluted skies, say NELM 4.5 and less?
How do the various specs contribute toward observing under bright skies? For example, magnification, aperture, FOV, exit pupil, eye relief, etc."
Right, get a 10x50.
Ron
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Fiske
Carpal Tunnel
Reged: 03/14/04
Posts: 2057
Loc: Missouri / United States
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Ron:
Yep. When all is said and done. When all the endless analysis of every possible parameter has been gone over for the umpteenth time. The best choice for hand-held, non IS binos under bright skies is a 10x50 OR (as I previously stated) a 10x42.
The only part of that advice you won't find in any basic astronomy book is that premium binos (Nikons, Zeiss, Leica, etc.) will be 10x42s and not x50s.
Pretty tough, huh?
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Fiske Miles
Nikon 8x42 LX / 12x50 SE Binos
Mini Borg 60ED, TV-101, AT80Ach, XT-8, C11/CI-700, 22-Inch Dob
Way too many Nagler eyepieces
http://www.fiskemiles.blogspot.com/
www.fiskemiles.com
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hallelujah
Carpal Tunnel
Reged: 07/14/06
Posts: 1639
Loc: Colorado Rocky Mt. High
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Quote:
premium binos (Nikons, Zeiss, Leica, etc.) will be 10x42s and not x50s.
Pretty tough, huh? Quote:
What about these? 
http://www.nikonsportoptics.com/product.php?group=14&subgroup=147&product=8209 Nikon AstroLuxe 10x70mm
http://www.zeiss.com/c1256bcf0020be5f/Contents-Frame/7c0c4ce74a32e9ed852571cb00499727 Zeiss Victory FL 10x56mm
http://us.leica-camera.com/nature_observation/ultravid_binoculars/ultravid_50_hd/ Leica Ultravid 10x50mm
http://www.swarovskioptik.com/index.php?c=produkte&l=us&nID=x434b769e932b90.44843491&css=&detail=usen1129112501__ID434ce3b56c5537.33086593&produktname=SLCnew 10x50mm
http://www.minox.com/index.php?id=644&L=1 Minox HG 10x52 BR asph
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Pentax 12x50mm PCF WP II FMC/WP/FP
Pentax 16x60mm PCF WP FMC/WP/FP
Pentax 20x60mm PCF WP II FMC/WP/FP
Orion 12x63mm Mini Giant FMC/JAPAN
Orion 15x70mm Little Giant II FMC/JAPAN
Orion 16x80mm Giant FMC/JAPAN
Orion 20x70mm Little Giant II FMC/JAPAN
Orion 30x80mm MEGAView FMC/JAPAN
Barska 30x80mm X-Trail LW FC
Burgess Optical Series II 20x90mm FMC/WP/FP
Handel's Messiah**Hallelujah! For the LORD God Omnipotent Reigneth
Edited by hallelujah (08/18/08 07:45 PM)
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BobinKy
scholastic sledgehammer
Reged: 04/27/07
Posts: 930
Loc: Country road
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Guys--
I was asking a sincere question. I will be taking some business trips in urban areas over the next few weeks. In the past, I have used a 10x50 roof or a 8.5x44 porro under bright skies, which did considerably better than a 6x32 roof I also had packed. My experience has been that magnification is the best approach to bright skies--unless I want to drive away from the bright skies, then aperture increases in importance.
Thanks for the replies.
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Bob
38° Kentucky, USA
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