New Posts New Posts RSS Feed - Really dumb Exit Pupil question
  FAQ FAQ  Forum Search   Events   Register Register  Login Login

Check GunBroker.com for SWFA's No Reserve and No Minimum bid firearm auctions.

Really dumb Exit Pupil question

 Post Reply Post Reply   Topic Search Topic Search  Topic Options Topic Options
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/19/2010 at 19:01
tpcollins View Drop Down
Optics Journeyman
Optics Journeyman


Joined: January/12/2009
Status: Offline
Points: 327
I'm almost embarrassed to ask this but what the heck. I have Zeiss 8x42 so I know the exit pupil is 5.25mm. At 63 years of age, my pupils probably don't get that large. In the past, I've had an Optimologyst put drops in my eyes that dilated the pupils to the size of dimes. If I went out to my hunting stand an hour before first light, put drops in my eyes to dilate my pupils, would I be able to see more detail in low light thru my binoculars versus if my eyes weren't dilated?
 
I said I was embarrassed to ask . . . thanks. 


Edited by tpcollins - August/19/2010 at 19:03
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/19/2010 at 22:08
Hitthespot View Drop Down
Optics GrassHopper
Optics GrassHopper


Joined: May/21/2010
Location: Ohio
Status: Offline
Points: 41
Well theoretically, It depends.  If your eyes are say 7 mm after dialating then 1.75 mm is just going to waste.  If your eyes at 63 will only dialate normally to 4 mm then after the drops they are 5.25 mm or bigger, then you will take advantage of the 1.25 mm increase in brightness.  It doesn't matter how much bigger than 5.25 mm they are because that is the size of the beam of light coming out of the binocular.   You can measure your pupil size.   You may find that even at 63 your eyes will dialate to around 5 or 6.  Everyone is different.  Do a web search on measuring your exit pupil.
 
Good Luck
 
Bill
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/20/2010 at 10:59
supertool73 View Drop Down
Optics Jedi Master
Optics Jedi Master
Avatar
Superstool

Joined: January/03/2008
Location: Utah
Status: Offline
Points: 9531
Umm, I don't think I would do that.  The times I have had my eyes dilated they have told me to stay out of the sun and wear sunglasses.  There is a reason your eyes contract in the light.  To force them open and to force more light in them cannot be good for them.  May just ruin your eyes completely. 

While I am no eye doc.  I would certainly suggest talking to one before attempting anything like that.  It just sounds all wrong to me.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/20/2010 at 11:22
ckk1106 View Drop Down
Optics Master
Optics Master
Avatar

Joined: December/14/2007
Location: Arizona
Status: Offline
Points: 1435
Originally posted by supertool73 supertool73 wrote:

Umm, I don't think I would do that.  The times I have had my eyes dilated they have told me to stay out of the sun and wear sunglasses.  There is a reason your eyes contract in the light.  To force them open and to force more light in them cannot be good for them.  May just ruin your eyes completely. 

While I am no eye doc.  I would certainly suggest talking to one before attempting anything like that.  It just sounds all wrong to me.

It sounds wrong to me also.  wrong, wrong, wrong.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/20/2010 at 11:29
Bird Watcher View Drop Down
Optics Master
Optics Master
Avatar

Joined: August/30/2006
Status: Offline
Points: 1490
Originally posted by tpcollins tpcollins wrote:

 If I went out to my hunting stand an hour before first light, put drops in my eyes to dilate my pupils, would I be able to see more detail in low light thru my binoculars versus if my eyes weren't dilated?
 
 
NO!
Do you remember how blurry everything was when you eyes were dilated?


Edited by Bird Watcher - August/20/2010 at 13:10
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/20/2010 at 13:05
tpcollins View Drop Down
Optics Journeyman
Optics Journeyman


Joined: January/12/2009
Status: Offline
Points: 327
I've had my pupils dilated before and remember how I had to wear sunglesses. I did say "an hour before first light" - I wasn't planning on it in the middle of the day. Whether I actually do it is irrelevant, but I'm trying to understand what improvement I might see.  
 
Hitthespot said if my pupils did dialate to 5.25mm, then "I could take advantage of it". But what exactly is the advantange - more detail in the low light compared to a dimmer view if my pupils only opened to perhaps 3.5mm?  Thanks.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: August/20/2010 at 13:26
Roy Finn View Drop Down
MODERATOR
MODERATOR
Avatar
Steiner Junkie

Joined: April/05/2004
Location: United States
Status: Offline
Points: 4856
Think of your eye pupil opening and closing much like the aperature of a camera lense. More light means more information for the brain to process through the optic nerve.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 10:52
tamanoir View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: June/25/2010
Location: France
Status: Offline
Points: 25
tpcollins, don't be embarassed with your question. There's no stupid question. I would complete the answers you received here by saying that these matters of entrance/exit pupil, eye's pupil and their net effect on vision is often misunderstood or answered with misleading information (I'm not talking about what I've seen here ! just generally speaking).
By estimating the brightness/dimmness of a bino, we must consider the "effective" diameter of the objective = minimum of (power X eye's pupil, physical diameter of the objective) ; it's the same as considering the "effective" exit pupil = minimum of (bino's exit pupil, eye's pupil).
In your example (exit pupil 5,25), and supposing a 100% light transmission by the bino (not true : the Zeiss FL, champion in this matter for the blue rays, has ~95% blue transmission as said by a comparative review of hunting night binos by a german periodic), we can conclude :
1) at 3,5 or 5,25 mm eye's pupil, the binos can give all the photons you need : by naked eye or with the bino you will have the same apparent brightness. The only, but big, advantage will be the magnification and all what is means, associated with the framing of the field of view (physiological effect : you're not disturbed by what is "outside").
2) with your 8x42, if you compare 3,5mm eye's pupil with 5,25mm (your original question) : the  advantage for 5,25mm will be (5,25/3,5)^2 = 2,25 X more light. In photography we would speak of 1 ev difference : very noticeable. More brightness with more low constrast detection ==> better gross resolution/identification too.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 11:01
tamanoir View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: June/25/2010
Location: France
Status: Offline
Points: 25
one more note : if your eye's pupil goes naturally to 5,25, chances are it is very dark. In these conditions our eye cannot perform with full resolution. With extreme pupils, eye's resolution goes down to ~10 times (not exact, just to give a scale) less its resolution by daylight : so big eye's pupil are not necesseraly a goal by themselves to see better even if it save your life by "detecting" this big bear coming at you in the forest by night :)
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 14:11
Steelbenz View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire
Avatar
ROLL TIDE ROLL

Joined: January/03/2006
Location: Heart of Dixie
Status: Offline
Points: 4915
Well Koshkin is better to anwser this but here goes. We all focus on exit pupil when really we need to think more in terms of resolution. The amount an wave length (colors) that pass thru the scope that hit our eyes is more important. This is a function of having better glass. That's why the saying buy the best glass not the magnafication is really important.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 14:27
saitotiktmdog View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: June/08/2010
Location: IN
Status: Offline
Points: 256
Theres no stupid question just stuped people....... Just kidding.   Sounds like a bad Idea to me.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 16:30
stickbow46 View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire
Avatar

Joined: January/07/2009
Location: Benton, Pa
Status: Offline
Points: 4673
Buy  better glass & save your eyes for looking at the grand children.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 17:20
jonoMT View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire
Avatar

Joined: November/13/2008
Location: Montana
Status: Offline
Points: 4618
It is an interesting question. I would think the main strikes against it are that everything would seem a bit blurry and it gets light pretty fast (seems like I always have to get into position well before daybreak at this latitude anyway). Exit pupil does play a part, which is why (in addition to avoiding the effects of shake) I prefer to keep magnification in bins @ 8X or below...to wring out as much as possible while keeping the size and weight down. While the better the glass, the better the view and less eyestrain, I have compared my monocular Swaro LRF glass with its 30 mm objective to looking through just one side of a pair of run-of-the-mill Nikon 8x42s in dim light and the larger objective made the Nikons more effective. But man, you could glass all day long with a pair of 8.5x42 ELs!
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 18:52
Gunshow75 View Drop Down
Optics Apprentice
Optics Apprentice
Avatar

Joined: December/23/2004
Location: Kentucky, USA
Status: Offline
Points: 209
Our eyes are able to function in bright sunlight and dim starlight, a range of about 10 million to one.  The part our pupils play in that range can be understood by looking at their ability to contract/dilate.  Our pupils can go from about 2 mm to 6 mm or 7 mm in some people, which is a range of about 10 to one. 
 
The affect of pupil diameter on binocular aperture is well known.  Even if it was medically okay, and like many others here, I don't think it is, the amount of brightness gain you would recieve by dilating your pupils is trivial when compared to the eye's ability to change its sensitivity.  Just get into the stand 30 minutes before daylight and let your eyes dark adapt. 
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: September/01/2010 at 18:52
tamanoir View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: June/25/2010
Location: France
Status: Offline
Points: 25
mmm, I'm afraid some of my remarks could have been seen as pretentious or like an attack. Excuse me if it the case ; I was only thinking of the classical advice we can seen too often when it comes to brightness in bino, for example "a 7x50 is brighter than a 7x35. Because pupil exit 7mm versus 5mm" : this is an other simplification that leads to erroneous conclusion. I was refering to that only because it has misleaded me a long time.
Steelbenz : the amount of any visible light, whatever wave length, that pass thru the SCOPE is a function of :
1) transmission ratio for this light through the scope ("better glass" = more transparent, less scattering, better antireflective layer, thickness of the glass, reflectivity of the mirror surfaces)
2) and the clear aperture of the scope (objective diameter if no internal mask)
All this light exits the scope via the exit pupil. This exit pupil = clear aperture / magnification.

Now, the amount of light, whatever wave length, that reachs the RETINA is a function of (I discard transmission ratio in the eye) :
1) the eye's pupil combined with
2) the exit pupil.
If the exit pupil <= the eye's pupil : all the light that passes through the scope will reach the retina.
If the exit pupil > the eye's pupil, the amount of light that reachs the retina corresponds only a part of the diameter's scope : this effetive diamter is eys's pupil X magnification.
Sorry to insits but that's facts.
Don't "believe" me ! Do this test : take a 8x42 and put a mask in front of it, say a mask with a clear aperture of 24mm during. Compare with and without the mask during a sunny day (to have your eye's pupil closed to 3mm or less).
You should see no difference in brightness.
Redo the same test, with and without mask, by night (to have your eye's pupil opened to say 5 mm or more).
You should a nice diffrence in brightness.
In the two case you have the same bino so the same transmission ratio. OK by night the spectrum isnt the same as daylight... but the comparison with/without mask is still valid, and you'll see by yourself the effects of exit's pupil and eye's pupil.
If you're not too picky with quality/transmission of the glass you could approche this little experiment by using a 8x42 and a 8x24 (or 7x21 or a 6x18 or 9x27...).
So, exit pupil and eye's pupil are an essential parameters from the standpoint of brightness.

I assume you, as I do often, include under this term the notion of "sharpness" (resolution+contrast+light level).
But strictly for resolution : of course it depends on the quality of the glass.
But it depends also, directly, on the clear EFFECTIVE aperture of scope, and so on the exit pupil combined with the eye's pupil.
By Dawes criterion, resolution (in arcsecond ") is 120/diameter (mm) : this is for the separation of to stars of magnitude 7.
By Foucault criterion, resolution is 137/d  : this for a pattern composed of a lot of evenly spaced lines black and white.
OK, these criterion are approximation for the green wave length (550nm) and what ever it is they are "only" references for comparison between scopes.
What I underline here, is that these formulas are function of the diameter of the entrance pupil, the effective diameter, that is the diameter (d) of the scope if exit pupil (exp) <= eye's pupil  (eyp), or the front projected diameter of the eye's pupil (eyp x magnification) if eyp < exp.
Dawes resolution (") = 120 / d, if exit pupil <= eye's pupil
Dawes resolution = 120 / (eyp x magnification) if eye's pupil <= exit pupil
(In fact this digression describe the sole effective resolution of the scope itself, and to estimate the effect on the retina we should take into account supplementary parameters such the limit of resolution of the eyes itself, but the principle remains valid)

So you see, exit pupil + eye's pupil are key parameters for brightness and for effective resolution too !

That said, I would take this into account only to optimise my choice of the bino depnding on the supposed conditions of usage : no need to be a 7x50 if I know I will not go more than 5 mm eye's pupil.
Then, a 7x35 would give my absolutly all what it needs, brightness and resolution wise (and depth of field too !! but that's an other subject). I could have a less burden.
But I could say mylself that at my maximum of 5mm exit pupil=eye's pupil, alignement will be propblematic and that a bigger exit pupil is then advantage. Idem for a sailor : a 7mm exit pupil will be much more confortable than a 5mm when my eye is 5mm.

All this text just to say that : pupils are key important parameters.

That said, in practice it's evident that the quality of the glass is of most importance, whatever the pupils, diameters ets, : a quality glass will always be better than an bottle's bottom glass.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/04/2010 at 21:08
Cajun Hunter View Drop Down
Optics Apprentice
Optics Apprentice


Joined: February/20/2007
Status: Offline
Points: 58

In addition to what was posted.  This is what is also important to me.  The larger the exit pupil of the bino the more stable the bino will be.  This is important for me while hunting.  Sometimes holding bino with one hand or something.  It is just a more enjoyable viewing experience to me.

Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/05/2010 at 01:39
mpk View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: January/15/2010
Status: Offline
Points: 26
I never understood why synaptic transmission by retinal photoreceptors is usually ignored in these discussions. It plays a major role in visual acuity. Adaptation to rod-mediated vision in low light allows much less resolution because of the larger receptive fields of rod bipolar cells. If sufficient light from a target reaches the fovea, as when you would be focusing on a deer at dusk or dawn, high-acuity cone-mediated vision can occur. It would seem that better quality glass with higher transmission could be more useful than slight changes in the exit pupil- it depends on details of both the scope optics AND the state of the retinal neurons as to which is actually limiting the perception of the target. It is a lot more complicated than I think most people realize. I'd like to hear what Ilya thinks also.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/05/2010 at 07:14
jonoMT View Drop Down
Optics Master Extraordinaire
Optics Master Extraordinaire
Avatar

Joined: November/13/2008
Location: Montana
Status: Offline
Points: 4618
Originally posted by mpk mpk wrote:

I never understood why synaptic transmission by retinal photoreceptors is usually ignored in these discussions.

'Cause most of us have no idea what that means. But thanks for the explanation. I will say that, empirically speaking, glass quality really does matter more than you'd think it would. I mentioned this in another post, but Premier Reticles' glass @ 15X is better for spotting bullet holes 300 yards away than a budget spotting scope @ 36X.

I get by with a pair of Nikon ATB binoculars but would much prefer my friend's Swaros. You could look through those all day without any eye fatigue.
Post Options Post Options   Thanks (0) Thanks(0)     Back to Top Direct Link To This Post Posted: October/08/2010 at 05:44
tamanoir View Drop Down
Optics GrassHopper
Optics GrassHopper
Avatar

Joined: June/25/2010
Location: France
Status: Offline
Points: 25
I think we should not oppose the different aspects (pupils vs transmission vs eye's behavior, etc) : all integrates in the global image and has its importance. In function of multiple conditions, one or the other can have more importance, yes, but all have their impact and interact together finally.
 Post Reply Post Reply
  Share Topic   

Forum Jump Forum Permissions View Drop Down

Similar Threads: "Really dumb Exit Pupil question"
Subject Author Forum Replies Last Post
30mm and exit pupil question obi-wan Rifle Scopes 5 12/15/2004 5:36:08 PM
Exit pupil Stud Duck Binoculars 5 8/1/2005 2:08:09 PM
Exit pupil Javali Rifle Scopes 2 8/31/2006 8:33:49 AM
Exit Pupil Question Quoddy Rifle Scopes 2
Exit pupil TexasPhotog Rifle Scopes 5
FoV and Exit Pupil question tpcollins Rifle Scopes 4
There's a difference in 4.0 and 5.25 exit pupil tpcollins Binoculars 0
Optic size verses exit pupil..? windstrings Binoculars 13 11/5/2007 6:05:39 PM
Exit Pupil 44 vs 50 flashpoint Rifle Scopes 1
Exit Pupil and Brightness Question... matthewdanger Binoculars 12


This page was generated in 0.344 seconds.