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Exit pupil

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Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/29/2005 at 08:37
Stud Duck View Drop Down
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At what point will the human eye notice a difference in the exit pupil of a binocular during low-light conditions? (All other factors being the same.)

 

I guess what I'm saying is.....can the human eye discern differences between an exit pupil of 5mm to say 6mm? What would be the smallest difference the eye could distinguish (Generally speaking)? At what point would it be beneficial to go with a binocular (top-end glass) with a higher exit pupil?

 

I hope I'm not splitting hairs here......

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/29/2005 at 11:12
David View Drop Down
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Our eyes tend to dilate smaller as we grow older.  A young persons eyes may dilate at 7mm, where as we get older, that number will drop to 5.  If you pick your magnification vs. the objective size, try to get between 5-7 mm, and you will get maximum performance out of your optic in any light condition.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: July/30/2005 at 17:41
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On top of that we all have somewhat different light sensitivity in our eyes.  This light sensitivity is what controls how much your pupils dilate. Some people's pupils fully dilate only when it is pitch black.  Some of this sensitivity (or insensitivity) is also acquired thorugh exposure to sun (without sunglasses), etc.

 

An additional consideration is that a larger exit pupil allows more leeway in eye position; i.e. if your eye is not positioned perfectly behind the ocular you still utilize all of your pupil.

 

Ilya

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/01/2005 at 12:12
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I'm probably all wet here, but I seem to recall reading an optics report a few years back that you could have too large an exit pupil too.  It seems that the point the author was making was that if the exit pupil were, say... 10mm across, the inability of the eye's pupil to expand above 7mm would result in a vignette affect that led to shadows/lack of clarity at the edges of the image.

 

Like I said, it was a few years ago and as I recall it came from one of the manufacturer's websites instead of just another post on a forum...  I could be mistaken after all this time, but as I recall the premise seemed plausible enough in the way it was presented at the time.

 

Anyone else with a thought?

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/01/2005 at 12:57
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I agree with that, but how sensitive is the human eye? Can it distinguish the "difference" between a 5mm exit pupil and a 6mm?

 

What I'm driving at here is, will I be able to tell the difference between a set of Swaro 10x42mm binoculars with a 4.2 exit pupil and a set of 10x50mm binocular with a 5mm exit pupil....etc,etc.....

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/01/2005 at 14:08
gremlin View Drop Down
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To answer your question, all things being equal, yes if you were in a condition of low light to begin with.

 

At high noon outside looking into the limbs of an oak tree in the middle of an otherwise vacant lot, a 10x50 would appear much the same level of brightness as a 10x40.

 

At 7:30 that same evening, it would be a different story, based upon my own experiment.

 

My own experience has held that a pair of Bausch and Lomb Custom 10x40's are not as bright as my 8x36 Customs side by side in low light conditions--the colors in the 8x36 are brighter.  However, the 10x40's are able to resolve the details of the bark in the same tree somewhat better side by side in low light conditions.

 

That's a case where comparable coatings and glass rule out different levels of brightness based upon manufacture and must instead be the result of different exit pupils.

 

Having said that, however, it depends on what you want to get out of the binocular.  Better color isn't necessarily better detail.

 

If you jump between manufacturers, the comparative difference in coatings makes it an even more difficult question to answer.

 

Can your eye distinguish the difference between identical binoculars with the only difference being exit pupil size?

 

Yes.

 

Can the difference be mitigated by varying qualities of coatings, glass, internal construction, and the like?

 

Yes.

 

I own 25 different pairs of binoculars and have had a dozen more pair that I've either traded in or sold.  Objective size makes a HUGE difference in the ability to resolve detail.  Exit pupil only makes a difference when all other factors are at least comparable.  Nothing matters as much as quality multi-coatings and construction tolerances.

 

Just my two cents...

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Take the long way home.

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