Exit pupil and eye relief - physical and conceptual models (1 Viewer)

[Vespobuteo]

The model of the exit pupil vs the eyes is often shown as there would be parallell lines of light from the ocular entering the eye pupil. I this a valid model or just a conceptual model?

Look at this video from Swarovski, first seconds.

https://www.youtube.com/watch?v=QVfp49RoBcI

It sure does look like that it's more of a cone of light since the size of the projection is changing. (They also say cone in the video)

I Also find it strange that parallell rays could have a focus point at a fixed eye relief.

To me it seems that what is happening is that the oculars are projecting an image of the exit pupils size at the distance of the eye relief.

This "cone model" is also shown in wikipedia
(but wikipedia have been wrong before..):

https://en.wikipedia.org/wiki/Exit_pupil

(see attached photo)

But when doing the experiment of shining a light through the bins and holding a piece of paper in different distance from the oculars
it seems like a plausible model (just like in the swaro video).

Could these images that are showing parallell lines hitting the eye from the ocular be more of conceptual models showing exit pupil size rather than the an actual physical ray tracing model?

These conceptual models also seem to imply that you would not see more than 10% of a 6 mm exit pupil in daylight if having a 2mm eye pupil.
I think that seems a bit strange.

Just curious and slightly confused.
:smoke:

 

[WJC]

The model of the exit pupil vs the eyes is often shown as there would be parallell lines of light from the ocular entering the eye pupil. I this a valid model or just a conceptual model?

Look at this video from Swarovski, first seconds.

https://www.youtube.com/watch?v=QVfp49RoBcI

It sure does look like that it's more of a cone of light since the size of the projection is changing. (They also say cone in the video)

I Also find it strange that parallell rays could have a focus point at a fixed eye relief.

To me it seems that what is happening is that the oculars are projecting an image of the exit pupils size at the distance of the eye relief.

This "cone model" is also shown in wikipedia
(but wikipedia have been wrong before..):

https://en.wikipedia.org/wiki/Exit_pupil

(see attached photo)

But when doing the experiment of shining a light through the bins and holding a piece of paper in different distance from the oculars
it seems like a plausible model (just like in the swaro video).

Could these images that are showing parallell lines hitting the eye from the ocular be more of conceptual models showing exit pupil size rather than the an actual physical ray tracing model?

These conceptual models also seem to imply that you would not see more than 10% of a 6 mm exit pupil in daylight if having a 2mm eye pupil.
I think that seems a bit strange.

Just curious and slightly confused.
:smoke:

Please see the thread: "10x50 EL or 10x54 HT"; I have explained.

Bill

 

[Mark9473]

With all respect Bill, that wasn't much of an explanation.
If the light exiting the binocular is a parallel ray, why is there something like "eye relief"?
What's the situation with people normally wearing glasses?

 

[Vespobuteo]

Please see the thread: "10x50 EL or 10x54 HT"; I have explained.

Bill

The theoretical illustration on how it may look like,
I have seen lots of times.
But to me it doesn't match the empirical findings
and the behavior of the exit pupil projection
in the movie clip.

An it doesn't match he wikipedia illustration.

It's something fishy here.

 

[Troubador]

VB
I am sure you are right: the light exiting must be a cone reaching a focus point at the ER position.
A parallel sided ray of light could surely not be in focus all the way from it's source to infinity.

Lee

 

[henry link]

The Wikipedia representation is accurate. The real physical light does emerge from the eyepiece as a cone or perhaps more accurately as two cones connected at the eye relief distance by a neck with the diameter of the exit pupil. in the image below I photographed light emerging from the eyepiece of a Zeiss 8x42 FL by placing a white card behind the eyepiece parallel to the optical axis. Tilting the card slightly allows the light to graze the paper revealing the hourglass shape of the light as it converges at an angle corresponding to the apparent field angle to form the exit pupil image of the binocular objective at the eye relief distance, then diverges beyond that.

What probably causes confusion is that what comes to focus at the exit pupil is an image of the binocular's entrance pupil, not a little image of the scene being observed in front of the binocular. Light from the scene is afocal at the eye relief distance behind the eyepiece just as if it were light falling directly from the scene onto the lens of the eye.

 

[Kammerdiner]

I have no idea about the details of eye relief and exit pupils, but every time I pick up the Swaro 8x32 SV I think, "OK, these guys have some tricks up their sleeve."

I've never seen an 8x32 like it for ease of view, with glasses anyway. The Zeiss 8x32 FL is a little fussbudget in comparison. The Nikon 8x32 SE is fussier still. I sold it.

What's going on? I think it's baffling. No, really. At least in part I think it's baffling.

Mark

 

[Vespobuteo]

The Wikipedia representation is accurate. The real physical light does emerge from the eyepiece as a cone or perhaps more accurately as two cones connected at the eye relief distance by a neck with the diameter of the exit pupil. in the image below I photographed light emerging from the eyepiece of a Zeiss 8x42 FL by placing a white card behind the eyepiece parallel to the optical axis. Tilting the card slightly allows the light to graze the paper revealing the hourglass shape of the light as it converges at an angle corresponding to the apparent field angle to form the exit pupil image of the binocular objective at the eye relief distance, then diverges beyond that.

What probably causes confusion is that what comes to focus at the exit pupil is an image of the binocular's entrance pupil, not a little image of the scene being observed in front of the binocular. Light from the scene is afocal at the eye relief distance behind the eyepiece just as if it were light falling directly from the scene onto the lens of the eye.

Thanks Henry,
very illustrative photo

 

[Troubador]

The Wikipedia representation is accurate. The real physical light does emerge from the eyepiece as a cone or perhaps more accurately as two cones connected at the eye relief distance by a neck with the diameter of the exit pupil. in the image below I photographed light emerging from the eyepiece of a Zeiss 8x42 FL by placing a white card behind the eyepiece parallel to the optical axis. Tilting the card slightly allows the light to graze the paper revealing the hourglass shape of the light as it converges at an angle corresponding to the apparent field angle to form the exit pupil image of the binocular objective at the eye relief distance, then diverges beyond that.

What probably causes confusion is that what comes to focus at the exit pupil is an image of the binocular's entrance pupil, not a little image of the scene being observed in front of the binocular. Light from the scene is afocal at the eye relief distance behind the eyepiece just as if it were light falling directly from the scene onto the lens of the eye.

Super pic Henry!

Lee

 

[WJC]

With all respect Bill, that wasn't much of an explanation.
If the light exiting the binocular is a parallel ray, why is there something like "eye relief"?
What's the situation with people normally wearing glasses?

I thought the graphics would do the trick. The light from all angles will form a CONE. BUT, that cone ends (for image forming purposes) at the focal plane. It remains as such--12mm or three feet--until it is acted upon by the lens of the eye, as I thought my illustrations would show.

I guess, then, the question is whether we are talking about all light present at the scene OR the light that forms an IMAGE. One will allow you to see birds; the other will not.

Henry's photo is illustrative. But then, so were mine. I call upon your senses. I was trying to show that the CONE does not end at an infinitesimally small POINT--as shown by most advertisers--but is the result of an infinitely large number of cones ending at the same PLANE and forming an IMAGE. :cat:

Was that any clearer?
Bill

 

[Mark9473]

Thanks Bill. Much better. I'm all on board with the image plane formed at the eye relief distance; in fact I knew that already. It's the rest of the light before and after the image plane that is fuzzy and remains so - in both meanings of that word.

 

[Kammerdiner]

Ah well, Physics 101.

There's more going on and that's for sure.

But don't ask me; I only use the silly things, for years on end.

Mark

 

[WJC]

Thanks Bill. Much better. I'm all on board with the image plane formed at the eye relief distance; in fact I knew that already. It's the rest of the light before and after the image plane that is fuzzy and remains so - in both meanings of that word.

That's just the nature of the beast and only means something to the Opto-geeks out there.

I'm sorry I was not clearer the first time. You may note the original post was made about 4 a.m. Mountain Standard time. That's as good an excuse as any and I'm stickin' to it! :cat:

Cheers,

Bill

 

[jring]

Thanks to Henry for the great image - I think it cannot be demonstrated better!

Joachim

 

[[email protected]]

I have no idea about the details of eye relief and exit pupils, but every time I pick up the Swaro 8x32 SV I think, "OK, these guys have some tricks up their sleeve."

I've never seen an 8x32 like it for ease of view, with glasses anyway. The Zeiss 8x32 FL is a little fussbudget in comparison. The Nikon 8x32 SE is fussier still. I sold it.

What's going on? I think it's baffling. No, really. At least in part I think it's baffling.

Mark

I agree with you. The 8x32 SV is unmatched for ease of view. The 10x50 SV is a little easier yet. That is what makes it so enjoyable. Nice photos Henry. That is the way I always thought the light comes out of a binocular. A real photo is much better than a diagram.

 

[SuperDuty]

Someone can explain everything to me that happens between the bumpers of a Cadillac, what I really want know is how does it feel when I drive it. My intelligence level doesn't allow me to understand what comes easy to Henry and a few others, but I still like reading what they have to say.

Ah well, Physics 101.

There's more going on and that's for sure.

But don't ask me; I only use the silly things, for years on end.

Mark

 

[elkcub]

...

Could these images that are showing parallell lines hitting the eye from the ocular be more of conceptual models showing exit pupil size rather than the an actual physical ray tracing model?

In addition to Henry's excellent explanation, it might be worth looking at the Wiki diagram from a somewhat broader perspective, because it does more than simply show what the exit pupil is. In a simplified way it shows how the telescope works.

Note first that red, green, and blue rays enter the objective from the left, and that the rays of each color are parallel. Why? Because the rays of a given color hypothetically emanate from separate object points in space and are shown as parallel because the object points are considered to be infinitely distant.

Now note that the three rays of each color converge on a plane some distance before the second lens, which is the ocular. The image on this internal plane contains the outside scene, and the ocular lens then refracts the rays emerging from that image.

Finally, note that the red, green and blue rays that emerge from the ocular remain parallel, and only come together at the exit pupil in the same way they entered the objective (except reversed).

A critical fact is that the angle at which the the ray groups arrive at the exit pupil, and subsequently enter the eye, is steeper than they originally entered the objective, or would have entered the eye had the instrument not been used. This angular change accomplishes the sole purpose of the binocular/telescope: magnification.

I believe this is consistent and compatible with Henry's comments.

Ed

 

[WJC]

Hi Guys:

I’m sure most folks thought Henry’s photo was the last word on the subject, as if the drawings I presented (none of which were mine) were just wasted efforts. Sorry; no cigar. I feel confident Henry will agree with my continuation. Onacounta it doesn’t stop, there!

The best focal plane for most practical purposes is at “The Circle of Least Confusion.” Henry’s two cones meet at the focal plane. But, is the focal plane FLAT? Usually not. That means some of the rays (differing from the incident height, and also wavelength) will focus before the focal plane and some will focus after. Thus the lens designer is looking for “The Circle of Least Confusion.” For VISUAL work, he will usually assign that to be the focal plane.

Even so, we are not out of the woods, yet. The optical system is made up from a series of curved surfaces. Thus, that focal plane is curved—usually convex to the sky. Even the “Flat Field Fujinon” is not photographically flat. It is, based on the threshold of recognition for most of us, flat enough. But, photographically? No way!

Yes, I can be bullheaded. But, I will let my original posts stand as delivered. Please note illustration #4, attached. It comes down to whether we are talking about light for light's sake or the light that forms an image. There may be two camps. If there is, I will admit being in the second, finding it to be the most practical for my needs.:cat:

Bill

PS Regardless of how many photos you have seen of RMS Titanic, it had only 3 “SMOKESTACKS.” Greater knowledge of the subject would explain my remark. The same thinkology is at work in optics.

 

[kkokkolis]

Regardless of how many photos I have seen of RMS Titanic, it had always 4 smokestacks. Is there an inner meaning in that phrase I lost in translation?

 

[kkokkolis]

Got it! The fourth funnel was a dummy.