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#1 Paul67

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Posted 08 August 2020 - 06:10 AM

Morning all, I am a complete novice and have no experience with binoculars or optics. If I have 20X50 binoculars does that mean because there are 2 X 50mm lenses I get the equivalent of a 100mm telescope aperture?

#2 scottinash

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Posted 08 August 2020 - 07:03 AM

I’m sure there will more educated binocular experts that will chime in here popcorn.gif but I think a pair 50mm binoculars will have the light gathering potential equivalent to a 70mm scope (basically a 1.4 factor). However, there are benefits that go along with both your eyes getting input at the same time as opposed to only one eye. Exit pupil, quality of the binocular objectives, prisms, etc all come into factor as well.     

 


Edited by scottinash, 08 August 2020 - 07:15 AM.


#3 DeanD

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Posted 08 August 2020 - 07:13 AM

Hi Paul, and welcome!

 

There are two issues here.

 

1) The resolution of a telescope/binocular is dependent on the diameter of the objective lens: the bigger the lens, the better the resolution (ie: you can see finer detail). So a 100mm lens will resolve finer detail than 50mm, even when both eyes are involved.

 

2) The brightness of the view at the same magnification is a function of the area of the lens (proportional to the square of the diameter). 2, 50mm lenses as in binoculars have a combined area equivalent to a single lens of ~70mm diameter (ie: 50x sqrt2)

 

There is some debate about this, but basically it means that because our brain adds the views from each eye, binoculars will give roughly equivalent views (in brightness and contrast as far as your brain is concerned) to a single lens of ~ 1.4 x the diameter of the binocular lens at the same magnification. They won't have the resolution of a 70mm lens though.

 

I hope that makes sense!

 

All the best,

 

Dean



#4 sg6

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Posted 08 August 2020 - 07:17 AM

Morning all, I am a complete novice and have no experience with binoculars or optics. If I have 20X50 binoculars does that mean because there are 2 X 50mm lenses I get the equivalent of a 100mm telescope aperture?

No.

A 50mm front lens is only 1/4 the area of a 100mm, so even both lens of a binocular are only collecting 1/2 the light that of a 100mm scope.

 

Next if you had a 100mm scope you use one eye, so all the light from it, 4x as much, is going to one eye. A binocular feeds each 50mm worth to one left eye and one right eye. So each eye gets only the 50mm worth.

 

Binosulars are sometimes more "natural" as you have both eyes open. And that is really the main aspect. They can be a lot more comfortable and so easier on the observer.

 

But no, two 50mm objectives do not make a 100mm objective, and unless you can combine the 2 optics they will never even make a 71.1mm = Sqrt((2*50))2

 

And evey "combiner" I know of is also a splitter so the "combined" aspect is then half of each input, and you are back to a 50mm objective (approximately).

 

If you want 100mm get a scope, or spend a few thousand $$ on a proper astro set of angled eyepiece binoculars.



#5 TOMDEY

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Posted 08 August 2020 - 08:05 AM

It is equivalent to total integrated entrance pupils' area. So the bino delivers as much information to your brain as a 71mm monoscope. At 20x (10x/inch) it's not taxing the resolution, so the root two factor is really quite accurate. Nother advantage of bino is that our brains filter out uncorrelated L/R noise (both static and dynamic)... things like floaters, cosmic ray hits, blind spots, retinal flaws, differential residual aberrations (of binos, eyes, and atmosphere)... which manifests as better brightness, contrast, and resolution. Also depends a lot on what you are scrutinizing.   Tom



#6 Paul67

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Posted 08 August 2020 - 10:19 AM

Thanks all I didn't realise there was a formula to work it out but it makes sense as there are formulae for telescopes. sg6 I do have a telescope but one at the basic end of the scale with a 114mm aperture. The other night I was sitting in my garden just looking with my eyes and the thought went through my head about having some binoculars. I was thinking maybe I could see a greater field with two eyes as opposed to the reduced field using one eye. Paul

#7 Mr. Bill

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Posted 08 August 2020 - 01:46 PM

Careful.....binocular viewing, especially astronomical, is addictive.

 

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