DblVision
professor emeritus
Reged: 10/11/06
Posts: 549
Loc: 29.99N 92.15W
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Hi Folks:
Despite repeated visits to the "CN Binocular Library", I don't think that I fully grasp what happens when exit pupil is larger than eye pupil. Reduced effective aperture is easy enough. What muddles the issue for me is when exit pupil illumination enters the equations, e.g. 6mm eye pupils and 6.67mm exit pupils from my 10.5x70's that are, say, 90% fully illuminated (Guess ONLY). Does this mean that I am effectively operating with 100% illuminated exit pupils from 63mm apertures? In more general terms, is illumination a factor in the large exit pupil / small eye pupil / effective aperture discussion?
Confession - Question driven as part of effort to better understand (Justify???) the tradeoff accepted by the decision to go with 10.5X rather than 15X. Reasons such as "ease of use", and long effective eye relief for use with glasses (I need 18mm to see the field stops, which I like to see) still hold true. The bins have also satisfied the "multiple user" criterion; By setting the IPD at "Tight" for me, I've had several folks, young and old, walk up to the tripod and experience the view without problems. Last night was a bummer, though; (a)The youngsters wanted no part of M46 / M47, "42F" had them say "No way!", and (b) Instead of a fresh, early a.m. start under Mag 5+ skies I went out late and fatigued under a soon-to-be-cloudy Mag 4.5 (est) condition. The difference was startling.
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Neal
G.O. Sig 10.5x70
Swift 761 8X42
60mm Spotter
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Erik D
Carpal Tunnel
Reged: 04/28/03
Posts: 2554
Loc: Central New Jersey, USA
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Quote:
Hi Folks:
.... What muddles the issue for me is when exit pupil illumination enters the equations, e.g. 6mm eye pupils and 6.67mm exit pupils from my 10.5x70's that are, say, 90% fully illuminated (Guess ONLY). Does this mean that I am effectively operating with 100% illuminated exit pupils from 63mm apertures? In more general terms, is illumination a factor in the large exit pupil / small eye pupil / effective aperture discussion?
I believe light is collected using all of the 70mm objectives but since your eye pupils do not open sufficiently to accept all 6.67 mm cone of light your eyes can not use the "spillover" light. This is no different from using 8X42 or 10X42 mm binos in the day time. Since the pupils do not dialate to 5 or even 4mm in bright light the bino is operating as a smaller 8X24 or 10X30. Even so, Bigger exit pupils are more accomdating becasue eye postions is less critical.
I usually prefer exit pupil no bigger than 5 mm for astronomy. I can see the brightest image in low power binos with 6-7mm exit pupil, but most of what I see empty grey sky with a few stars few and far in between from my mag 4-4.5 backyard. M 45 looks tiny and totally impressive. 12X50 is better, 20X80 magnificient!
ERik D
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Mark9473
Carpal Tunnel
Reged: 07/21/05
Posts: 2699
Loc: 51°N 4°E
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Neal, the percentage exit pupil illumination is a certain value at a certain distance from the optical axis. The edges will be less illuminated than the center. If you're sampling only the central 6 mm of a 6.67 mm exit pupil, you're seeing a better illuminated cone of light than if you were using a binocular with 6 mm exit pupil and the same percentage light fall-off towards the edge. This would theoretically give a brightness advantage, however there are of course many other design parameters that play a role in that.
From my recent experience with my 7x50s, I would add that using a binocular with exit pupil closely matching the eye pupil requires a more precise positioning of the eyes to avoid seeing a darkening. If the exit pupil is either larger or smaller, there is more tolerance on how steady you have to hold the binoculars.
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63
WO Megrez II 80 FD + Baader 90° T2 Amici
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KennyJ
Reged: 04/27/03
Posts: 10146
Loc: Lancashire UK
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Neal ,
It looks like EdZ is still away from his desk !
My own opinion on this matter is not necessarily that of many others here , but I look at it this way .
SO WHAT if the exit pupil of a binocular happens to be 1.5 millimetres , one millimetre , or in some cases fractions of a millimetre LARGER than the eye entrance pupil ?
Frankly , I think there are FAR MORE IMPORTANT factors to consider and much more to worry about when considering a binocular purchase , than the technical consequences of using a 7 x 50 binocular when your eyes may only be dilated to 6.25mm , or whatever .
You mentioned EYE RELIEF and SEEING THE FIELD STOP , and already you have touched upon TWO aspects which are far more important in my book .
What about the overall optical quality and various aberrations ? coatings ? prism types ? field of view ? false colour ? image sharpness ? contrast ? -- how about spherical aberration of the exit pupil ? :-)
How about BUILD quality ? -- focus mechanisms ? diopter range ? eyecup types ? collimation ? serviceability ? waterproof ? fogproof ? fit and finish ? weight ? image stabilisation or not ? ease of mounting ?
What about the little matter of magnification and sheer SIZE of the binoculars ? are they easily portable ? are they BIG enough for useful astronomy ?
The list goes on -- and on -- and on !
Debates go on -- and on -- and on !
Everyone from professors to plumbers to pancake tossers seem to have joined in the debates over the years :-)
For ME -- if a binocular is basically a GOOD binocular , such as a Nikon Prostar or Fujinon FMTSX or Swarovski EL , and if it has sufficient eye relief ( note the FMTSX 16x would NOT have for ME personally ) -- then I wouldn't worry overmuch about " lost " aperture in the event of the situation put forward .
Now I'll wait and see what the REAL experts have to say :-)
Oh -- and more importantly than ANY of the above , GOOD EYESIGHT and CLEAR SKIES ! :-)
Kenny
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If everyone is thinking the same thing , no-one is thinking - General George S.Patton
Zeiss 7 x 42 BGAT
Captain's Helmsman 7 x 50
Nikon 10 x 42 Superior E
Swift Audubon Kestrel 10 x 50
Helios 15 x 70 Observation
Strathspey 20 x 90
Televue 76 APO
Zeiss 85 Diascope
Helios 102 f5 refractor
Various eyepieces barlows tripods mounts etc.
Panasonic Lumix DMC - TZ5 digital camera
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Erik D
Carpal Tunnel
Reged: 04/28/03
Posts: 2554
Loc: Central New Jersey, USA
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Does it really matter what the "REAL experts" say?
One said our pupils don't open up to more than 2 mm in broad daynight but I centainly would want to use a bino with 2 mm exit pupil. I looked thru the Zeiss 7X42 Classic at the my local NJ Audubon center and liked it a lot. I would probably go with a 10X42 as an all around bino because I simply prefer higher power binos, not becasue I fear 6mm exit pupil is "wasted". I do know 4 mm or larger exit pupil is more comforatble in day time viewing.
Select a bino with sufficient magnification, objective size, FOV and feels right for YOU under your sky conditions and you'll be fine. I used my 7X50s and 10X40s for 15 years before I moved on the something else. If you need the ER of the 10.5X70 then it's the right one for you.
ERik D
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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Pupils in an optical system are related to image brightness. Change pupil size and the image brightness changes (given equal magnification).
There are several pupils in a system - entrance pupil (aperture), exit pupil, and eye pupil. The entrance pupil and exit pupil are related by magnification. If I place an aperture mask on the entrance pupil, the exit pupil decrease by the same relative amount. If I place a mask at the exit pupil, the same thing happens in that the effective entrance pupil is reduced. This is what the eye pupil does when it becomes smaller than the exit pupil. The smallest constricting pupil defines the whole system.
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Alan French
Night Owl
Reged: 01/28/05
Posts: 1484
Loc: Upstate NY
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I would add that if the exit pupil produced at a particular magnification fully illuminates your pupil - that is, is larger or equal to your pupil size - you are getting the brightest view you can possibly get at that power. There is no need to fret about "lost light."
Clear skies, Alan
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patter1
professor emeritus
Reged: 01/19/05
Posts: 597
Loc: Canada
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Quote:
I would add that if the exit pupil produced at a particular magnification fully illuminates your pupil - that is, is larger or equal to your pupil size - you are getting the brightest view you can possibly get at that power. There is no need to fret about "lost light."
This is correct for extended objects - you'll be getting the maximum surface brightness any time that the exit pupil is at least as large as your eye's pupil.
But stars, however, won't be at their full brightness if you're not utilizing the full aperture. That's one thing Al Nagler's eyepiece article doesn't mention  .
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Patrick
8" f/6 NewStar dobsonian
Orion Starblast 4.5" f/4 mini dobsonian
42mm SuperView, 17mm Nagler T4, some other cheapies
Omcon 7x50, Oberwerk 11x56, Olympus DPS-R 7x35, Olympus Magellan 8x25
homemade 50mm right-angle bino-scope prototype
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Alan French
Night Owl
Reged: 01/28/05
Posts: 1484
Loc: Upstate NY
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Quote:
Quote:
I would add that if the exit pupil produced at a particular magnification fully illuminates your pupil - that is, is larger or equal to your pupil size - you are getting the brightest view you can possibly get at that power. There is no need to fret about "lost light."
This is correct for extended objects - you'll be getting the maximum surface brightness any time that the exit pupil is at least as large as your eye's pupil.
But stars, however, won't be at their full brightness if you're not utilizing the full aperture. That's one thing Al Nagler's eyepiece article doesn't mention .
Patrick,
It is true for anything you are viewing. If you have 7x50 binoculars, and your eye only opens to 5mm, you are getting all the light your eye can accept at that power . There is nothing you could do to get more starlight onto your retina at a magnification of 7x. You would, of course, be using more of the aperture if you increased the magnification.
Clear skies, Alan
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DblVision
professor emeritus
Reged: 10/11/06
Posts: 549
Loc: 29.99N 92.15W
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Thanks, Guys. I will be absorbing all of this. I don't mean to create a ruckus. This was initially intended to be a response to Kenny's query about difficult decisions. When I was ready to respond to that post, Zach Garrett had just posted and I felt the moment was not opportune.
I guess the bottom line question is the issue of the exit pupil being a bundle of light of equal intensity. If yes, then I can easily understand the "Effective aperture" statement. If no, then the illumination issue may be a factor.
Kenny, you, as always, bring out the both the pragmatic and the subjective nature of these devices. I've no qualms about the binos in question and plan to keep them for life. I relied heavily on CN data prior to purchase, with Zach's satisfactory reponses to numerous information requests clinching the sale. Unfortunately, this approach eliminates much of the trial and error through which much experience can be gained and comparisons can be made. A not unrelated example; I was approached by a fellow hunter and friend who asked about what optic to mount on his rifle. In short, I told him to spend at least what he had in the rifle. Two weeks later he showed up with a Swarovski costing at least 50% more than the rifle did. He remains happy to this day. He, and I, however, are not the persons whose experience with lesser quality goods generate such suggestions.
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Neal
G.O. Sig 10.5x70
Swift 761 8X42
60mm Spotter
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Mark9473
Carpal Tunnel
Reged: 07/21/05
Posts: 2699
Loc: 51°N 4°E
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Quote:
I've no qualms about the binos in question and plan to keep them for life.
That's good to hear Neal, also because it gives you time to do a mini-review on these 10.5x70...
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Mark
Leica 8x20; Vixen 8x42; Swift 8.5x44, 10x50 and 20x80; TS 7x50; Orion 15x63
WO Megrez II 80 FD + Baader 90° T2 Amici
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patter1
professor emeritus
Reged: 01/19/05
Posts: 597
Loc: Canada
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Quote:
Patrick,
It is true for anything you are viewing. If you have 7x50 binoculars, and your eye only opens to 5mm, you are getting all the light your eye can accept at that power . There is nothing you could do to get more starlight onto your retina at a magnification of 7x. You would, of course, be using more of the aperture if you increased the magnification.
Sorry Alan, my bad; I overlooked the part about magnification being fixed, in which case you're right. (I'm used to thinking in terms of scopes, where you can always increase the magnification if you're using such a low mag that you're not utilizing the full aperture).
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Patrick
8" f/6 NewStar dobsonian
Orion Starblast 4.5" f/4 mini dobsonian
42mm SuperView, 17mm Nagler T4, some other cheapies
Omcon 7x50, Oberwerk 11x56, Olympus DPS-R 7x35, Olympus Magellan 8x25
homemade 50mm right-angle bino-scope prototype
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DblVision
professor emeritus
Reged: 10/11/06
Posts: 549
Loc: 29.99N 92.15W
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Mark:
I've actually toyed with the idea. It's a bit scary, however, seeing the wealth of experience and knowledge at work here already. I reread the thread, including my post from last night. My comment about "lesser quality" goods struck me as possibly being construed as an insult. This is certainly not intentional. What I meant was that it is the person who has experience with many optics that can best gauge where a particular bin stands, a comparitive study. It's the folks like me that root through here gaining from the experience of others. Meanwhile, I think I'll spend a few more hours later on this Mardi Gras back at "The CN Binocular Library".
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Neal
G.O. Sig 10.5x70
Swift 761 8X42
60mm Spotter
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Alan French
Night Owl
Reged: 01/28/05
Posts: 1484
Loc: Upstate NY
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Quote:
Quote:
Patrick,
It is true for anything you are viewing. If you have 7x50 binoculars, and your eye only opens to 5mm, you are getting all the light your eye can accept at that power . There is nothing you could do to get more starlight onto your retina at a magnification of 7x. You would, of course, be using more of the aperture if you increased the magnification.
Sorry Alan, my bad; I overlooked the part about magnification being fixed, in which case you're right. (I'm used to thinking in terms of scopes, where you can always increase the magnification if you're using such a low mag that you're not utilizing the full aperture).
Patrick,
Not to worry - we've all been there from time to time. 
Clear skies, Alan
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johnirvine
member
Reged: 02/27/04
Posts: 53
Loc: Iowa
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Hello, I think Mark stated this above, but there is the issue of vignette which dims the outer portion of the exit pupil (there is a discussion of vignette in the 'best of' section dealie... very interesting.). That is, it may be that for a pair of bins with a exit pupil greater than the eye pupil's will present the viewer with more light because an exit pupil matched to the eye's pupil would be delivering an exit pupil with a dimming around its periphery.
Plus, I find that larger than ordinary exit pupils can be helpful in being not as finicky with eye placement as well as giving the observer a chance to "look around" the fov with out the image dimming or blanking out. I find this to be quite helpful when looking using averted vision on a dim object... it is just easier because I don't have to focus so much on my eye placement to ultilize averted vistion.
OK, I just realized that this post is completely superfluous as the same thing has been said several times. :-)
John
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There wolf. There castle.
Nikon E2 8x30, 10x35; Zeiss Classic 7x42; Swift Ultralite 9x63; Fuji 7x50 FMT-SX
Edited by johnirvine (02/21/07 11:15 AM)
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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Quote:
Hello, I think Mark stated this above, but there is the issue of vignette which dims the outer portion of the exit pupil (there is a discussion of vignette in the 'best of' section dealie... very interesting.). That is, it may be that for a pair of bins with a exit pupil greater than the eye pupil's will present the viewer with more light because an exit pupil matched to the eye's pupil would be delivering an exit pupil with a dimming around its periphery.
No, it does not proved more light or brighter image, but it could eliminate the vignetting. Vighnetting can be thought of as an aperture between a pupil and an image plane. It impacts both bightness like a pupil, but it encroches on the field like a field stop. Since vighnetting only affects off-axis illumination, stoping down the effective aperture either at the entrance or exit pupil can eliminate the effect on the image. However, since the binos are working at a smaller aperture, the whole image would dim giving less brightness then the unvighnetted image area at the full aperture would be.
Quote:
Plus, I find that larger than ordinary exit pupils can be helpful in being not as finicky with eye placement as well as giving the observer a chance to "look around" the fov with out the image dimming or blanking out. I find this to be quite helpful when looking using averted vision on a dim object... it is just easier because I don't have to focus so much on my eye placement to ultilize averted vistion.
OK, I just realized that this post is completely superfluous as the same thing has been said several times. :-)
John
Spot on. Rifle scopes are designed with very large exit pupil for the same reason that eye placement is far easier - or even possible.
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johnirvine
member
Reged: 02/27/04
Posts: 53
Loc: Iowa
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wilash,
OK I'm a little funcused... are you saying that if I have two bins one 10x70 and one 10x50 (both with the same focal ratios.. or rather a 10x50 not being a stopped down 10x70) with similar characteristics of vignette, i.e. proportionally similar loss of light off axis as you move toward the edge of the exit pupil, and you plunk an actual pupil in front of it the amount of light entering the eye is the same?
I can see where a 10x70 and that same 10x70 stopped down to 50mm would have the same light input on a 5mm pupil.
Am I even asking the right question?
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There wolf. There castle.
Nikon E2 8x30, 10x35; Zeiss Classic 7x42; Swift Ultralite 9x63; Fuji 7x50 FMT-SX
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johnirvine
member
Reged: 02/27/04
Posts: 53
Loc: Iowa
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Hmmm.. or are you saying that if I have identical bins with different eyepiece field stops, e.g. one that has a 60 deg. afov and one that has a 50 deg. afov, the dimming is going to be greater in the outer 10 deg. of the afov?
Sorry.
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There wolf. There castle.
Nikon E2 8x30, 10x35; Zeiss Classic 7x42; Swift Ultralite 9x63; Fuji 7x50 FMT-SX
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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Quote:
Hmmm.. or are you saying that if I have identical bins with different eyepiece field stops, e.g. one that has a 60 deg. afov and one that has a 50 deg. afov, the dimming is going to be greater in the outer 10 deg. of the afov?
Sorry.
Yes, you can put it that way. The other way is if you have vignetting in the outer 10% of the field when using the entire exit pupil, you can eliminate that vignetting by using less of the exit pupil (or aperture). The aperture stops (entrance and exit pupil), when made smaller, can cut off the portion of the system that is causing the vignetting. Vignetting is really the aperture being reduced when viewed at a certain angle off axis - this is why it is only seen at the edges rather than affecting the entire image equally. If you look down you binos on axis at a the exit pupils (hond the binos away from you; don't look through them), the pupils will be round. Rotate the binos so you are looking at the edge of the field by half the amount of the AFOV and you may notice the binos block part of the pupil creating an almond shape. The pupil is vignetted and since it is smaller, that part of the image is darker.
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wilash
Fairy Godmother
Reged: 09/30/03
Posts: 5746
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BTW, if you reduce the aperture or exit pupil so it appear round at the edge of the field, then vignetting is eliminated.
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