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Hi. I'm thinking of buying 7x80 binoculars. Has anyone done research of binoculars of this spec. or bought binoculars of this spec? Can any be recommended? Budget, say up to £150. Thanks.

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Posted (edited)

Assuming your wanting to use these for astronomy, if you divide the aperture 80 by the magnification 8 you'll end up with something like 11mm of exit pupil?
Holding the binoculars at arms length and looking at something bright  the small dots of light that you see in the eyepieces are the exit pupils!
For low light levels or astronomy,  having an exit pupil far wider than what your own eyes can achieve  is not constructive to best practice, and the extra light gathered will be wasted?
My eyes average 5mm  dilated, so in effect they  would  reduce the  aperture  of this  binocular to something similar to an  8 x 40.

Edited by Charic
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Agreed, not even sure they exists for the reasons explained by Charic.

I assume you are wanting low power widefield views? 7x50’s would give you just over 7mm exit pupil, about the max you will achieve without wasting light. If you want larger aperture then it makes sense to go to higher powers eg 15x70 or 20x80.

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You would need some pretty big pupils to make use of such a bino, better off with a 7x50, or 8x42.

Maybe this chap could buy the 7x80's:

 

images.jpg

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I'm a little rusty on this subject too , so found this very helpful image on Wikipedia - focus on number 3 and 4 especially ... 

0B1BDD87-98E5-458B-9827-DD607683A8B6.jpeg

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Hi there, I own a 11×80.

But I don't think they make that kind of low magnification with large aperture any more. The reason, exit pupil as mentioned before.

The best views I had were with a 15x70

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25 minutes ago, Eastman said:

Hi there, I own a 11×80.

But I don't think they make that kind of low magnification with large aperture any more. The reason, exit pupil as mentioned before.

The best views I had were with a 15x70

How do you find the 11x80s Eastman?

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Posted (edited)

To expand on Charic’s answer; the exit pupil of an optic (binoculars or telescope) is the objective diameter divided by the magnification. If this exit pupil is larger than the dark-adapted pupil size of your eyes you will not be able to see all the light collected by the lens. For example, if your dark-adapted pupil is 6mm a pair of 7x80 binoculars would give you the same image brightness as a pair of 7x(6mm*7x)=7x42. 

Peoples’ dark-adapted pupils vary greatly and decrease with age, from about 7mm for teens to about 4mm for geriatrics. Here is one of the best studies available:

https://homepages.uni-tuebingen.de//martin.adler/pup_age.html

You can measure your dark-adapted pupil size in a number of ways (google it). The most accurate is probably to take a flash picture of your eyes and a ruler in a dark room and measure your pupil size on a computer screen. 

Edited by martinl

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Posted (edited)
2 hours ago, Stu said:

How do you find the 11x80s Eastman?

Well........ to be honest, big clumsy and top heavy.

The Pollux has exit pupil of 7.2mm and I am not 25 years anymore:icon_biggrin:

So its more a 11x65.

20160326_151450.jpg

Edited by Eastman
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6 minutes ago, Eastman said:

Well........ to be honest, big clumsy and top heavy.

The Pollux has exit pupil of 7.2mm and I am not 25 years anymore:icon_biggrin:

So its more a 11x65.

20160326_151450.jpg

Funny :)

They look nice though, big chunky prisms in there!

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I do wonder if large exit pupils produce an image that is far easier to see in that you are not having to move your eye around trying to find the sweet spot.

Alan

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25 minutes ago, Alien 13 said:

I do wonder if large exit pupils produce an image that is far easier to see in that you are not having to move your eye around trying to find the sweet spot.

Alan

Hmmm, that's interesting? Thoughts, people?

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28 minutes ago, Alien 13 said:

I do wonder if large exit pupils produce an image that is far easier to see in that you are not having to move your eye around trying to find the sweet spot.

Alan

 

2 minutes ago, trynda1701 said:

Hmmm, that's interesting? Thoughts, people?

If you are using the binos hand held then there is definitely some benefit from an exit pupil somewhat larger than your dilated eye pupil as it will be easier to hold the image in view without those irritating dark areas when you 'lose' the image if the exit pupil is too small. That said, the 11.4mm exit pupil from a pair of 7x80s as others have said would be overkill. If your dilated eye pupil is say 5mm then 10x50 binos would theoretically be an exact match, but hand holding 10x50 so that they extactly matched your eyes would be challenging, so something like 10x70 may prove to be a bit more comfortable to use - you won't see anymore stars, but it might be easier to keep your retina illuminated with them rather than with the 10x50s. I have a pair of 15x70 (exit pupil 4.7mm) which are comfortable for sweeping the Milky Way from a prone position on a sun lounger, but very difficuly to hold steady in the hands, so perform better when mounted on a tripod.

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I know a lot of military spotting scopes and gun sights often have exit pupil diameters well over 20 mm.

Alan

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3 minutes ago, Alien 13 said:

I know a lot of military spotting scopes and gun sights often have exit pupil diameters well over 20 mm.

Alan

Yes, but this is a classic case of horses for courses. With gunsights, the main benefit of a large exit pupil is greater freedom to position the eye with respect to the optical axis. When you need to sight the gun quickly for a now-or-never shot, you don’t have the luxury of placing your eye behind the ocular with the same precision, so a large exit pupil enables you to quickly see what you need to see to take the shot, even if your eye is less than ideally positioned.

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1 minute ago, geoflewis said:

Yes, but this is a classic case of horses for courses. With gunsights, the main benefit of a large exit pupil is greater freedom to position the eye with respect to the optical axis. When you need to sight the gun quickly for a now-or-never shot, you don’t have the luxury of placing your eye behind the ocular with the same precision, so a large exit pupil enables you to quickly see what you need to see to take the shot, even if your eye is less than ideally positioned.

Agreed but I have looked through one of these instruments at astro targets and the views were stunning without any restraints, I was as if the optics disappeared.

Alan

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Posted (edited)
10 minutes ago, Alien 13 said:

I was as if the optics disappeared

I agree, that is definitely a benefit of the larger exit pupil, it's just that there is a point at which the extra aperture per magnification (larger exit pupil) yields no additional benefit as the limiting factor is your pupil's diameter. Once the exit pupil is sufficient to easily keep your eyes fully illuminated there is no gain in a greater exit pupil, but I agree that up to a point a larger exit pupil can provide a more immersive experience.

Edited by geoflewis
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3 minutes ago, geoflewis said:

I agree, that is definitely a benefit of the larger exit pupil, it's just that there is a point at which the extra aperture per magnification (larger exit pupil) yields no additional benefit as the limiting factor is your pupil's diameter. Once the exit pupil is sufficient to easily keep your eyes fully illuminated there is no gain in a greater exit pupil, but I agree that up to a point a larger exit pupil can provide a more immersive experience.

Thats spot on but I think people should view exit pupil size as something to experiment with. I agree that with increasing EP size you get a drop off in perceived brightness but wouldn't the image resolution remain the same.

Alan

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34 minutes ago, Alien 13 said:

Agreed but I have looked through one of these instruments at astro targets and the views were stunning without any restraints, I was as if the optics disappeared.

Alan

Alan

 

Interesting. What exactly were you looking thru when you tried this?

 

Mark

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14 minutes ago, Alien 13 said:

Thats spot on but I think people should view exit pupil size as something to experiment with

Definitely, but I think it is also relevant to point out that increased aperture at low magifications won't make the image any brighter as the 'brightness' is limited by the pupil's diameter. Our eyes are all different, even the two eyes that we each have and a younger person's exit pupil will likely be significantly larger than an older persons, so experimentation is definitely worthwhile.

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3 minutes ago, trynda1701 said:

Alan

 

Interesting. What exactly were you looking thru when you tried this?

 

Mark

It was an old right angled tank scope, from memory it was 6x70mm.

Alan

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