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mark RD

BINO QUESTION ????????????????

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Just wondering

would a large pair of binos ei 10x70 give a wider Field of view then say a pair of 10x50 ?

If so I imagine it would be the same with telescopes?

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I'm guessing the focal length of the 10x70s will be greater than the 10x50s, so they'd give a a narrower FOV.

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Hmm. 10 x 50 means 10 times magnification, 50 mm objective. So 10 x 70 will be the FOV but more light-gathering ability.

Arthur

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What I'm asking is would the Field of view change or would you just be able to see fainter objects

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I may well be wrong but I'd guess (all other things being equal) you get a narrower FOV caused by the longer focal length and (defineatly) be able to see fainter objects because of the bigger objective.

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10x70 exit pupil 7mm 10x50 exit pupil 5mm when you get older your eyes dont dilate to 7mm if the person is young they do . i am 61 so not much to gain with getting 10x70 so i have the 10x50 for my night sky observations ,but dont buy cheap big chinese bins may see More with quality instead of quantity,a lot of chinese stuff on the market under various names Some very good European glasses on the market and Japanese,you get what you pay for,and that applies to bins as much as any thing else :lol:

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... I'd guess (all other things being equal) you get a narrower FOV caused by the longer focal length and (definitely) be able to see fainter objects because of the bigger objective.

Gaz beat me to it :lol:

Although... Things are rarely 'equal' and (as with scopes) FOV is more a factor of eyepiece design than focal length. Two binoculars can have identical magnification and focal length but one can be fitted with a wide-field eyepiece.

Steve

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Ok Ill rey again,

Q Lets say I have a 60mm refractor with a focal lenth of 500mm and Im using a 30mm eyepiece, giving me a magnification of 16x

now lets say I put the same eye piece in a 100mm refractor also with a focal lenth of 500mm giving a magnification of 16 x

A The only difference would be that things would apear brighter.

Action ... I think I will stick to my 10x50s :lol:

Mark

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A The only difference would be that things would apear brighter.

Yes, although the 100mm will also produce a larger exit-pupil.

Steve :lol:

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A The only difference would be that things would apear brighter.

Yes, although the 100mm will also produce a larger exit-pupil.

Steve :lol:

Right

So now we get to what I wanted to know :lol: what are the benifits of a larger exit-pupil?

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It depends how big your pupils are. If the exit pupil of an optical instrument is larger than your dark adapted pupil (which shrinks as we get older) then the extra brightness is lost to you.

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AS a quick example.

In a 8" f6 scope a 40mm Plossel will give x30 mag and an exit pupil of 6.66, a similar 32mm Plossel will give x37.5 mag and a 5mm exit pupil.

If you dark adapted pupil is only around 5mm the image will not be any brighter in the 40mm than it is in the 32mm, you just don't 'see' the extra light as it falls outside of your pupil.

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... what are the benefits of a larger exit-pupil?

Ideally, the diameter of your eye’s pupil will be the same diameter as the eyepiece exit pupil, then your eye will comfortably receive all of the light from the eyepiece and the image will appear as bright as it can possibly be.

If your eye-pupil is smaller than the exit-pupil, some of the available light within the exit-pupil will be wasted and the image will appear darker.

If the exit-pupil is significantly smaller than your eye-pupil (I bet your beginning to regret asking :lol:) then the narrow beam of light will pick out 'floaters' within the eye and eyelashes, which is distracting to say the least.

It is worth noting that the eyes maximum pupil size diminishes with age. Someone in their twenties might easily achieve 7mm but at around 50, this will probably have reduced to 5mm.

Hope that helps,

Steve :lol:

PS: Don't overly worry about details like this... It can lead to 'paralysis thru analysis'!

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