Telescope with expanded exit pupil (1 Viewer)

Exit pupil is a key parameter of binoculars, telescopes and spotting scopes. It is also closely associated with eye relief:

Exit pupil: the imaginary disk behind the eyepiece where the rays from the eyepiece converge. The observer must place his eye on this disk to be able to see the full field of view.

Eye relief: the distance between the exit pupil and the last eyepiece lens.



With reference to the above picture, there is an area (rhombus shaped) that is covered by both the central exiting beam and the beams from the far edges of field of view. As long as the eye is placed within this rhombus, it will see the entire field of view (not necessarily with even brightness, but usually OK).

In Keplerian telescopes, the exit pupil diameter is determined by the diameter of the objective lens divided by magnification (power). So, 10x50 binoculars will have an exit pupil 5mm in diameters, 10x32 binoculars will have a 3.2mm exit pupil, etc.

It is very difficult to view the image of a telescope which has a small exit pupil. This is unfortunately the case with most spotting scopes. Their exit pupil is usually about 1.5mm to 3mm in diameter.

In the past few years I have been studying, testing and patenting techniques that can expand the exit pupil of an eyepiece. By this I mean designing an optical device whose exit pupil is larger then the value calculated above. There are several advantages to this design:

a) Large exit pupil makes lateral eye placement uncritical. The larger the exit pupil, the less critical it is to position the eye exactly on the optical axis.

b) Large exit pupil makes longitudinal eye placement uncritical as well. With a large exit pupil, the eye can be before or after the eye relief distance and it will see a reasonable image. The optimal position remains the same (at eye relief) but it is not longer critical for seeing "an" image.

Here is an example of a rifle scope with expanded exit pupil:



The following image is taken from more than 1m distance from behind the scope. Note, how there is no "pupil", the entire eyepiece face is illuminated. You can still see an image through this scope even if you move 30 degrees to the left, right, up or down from the optical axis.





I am creating this thread to open discussion of this topic. I am hoping that it will create awareness and lead to a better understanding of this technique for use in binoculars, spotting scopes and rifle scopes.

Two video demos of this concept:

Demo 1

Demo 2

Doesn't "Plossl" sound so much cooler and more expensive than "symmetrical doublet"?

Omid:

Considering your audience here, I doubt you are going to get much participation. Cloudy Nights would be a little better, but not by much. In addition, it's not safe for postdocs to hang their hats there. Wannabes will come out of the woodwork to set you straight about things they can't even pronounce.

There are some optical engineering forums out there, but, for some, you need to be invited in by a member of the group. In addition, some were well-known optical engineers before you were born. They're welcoming, but not easily impressed.

Cheers,

Bill

It's cool but it's so far over my head I didnt even hear the whoosh when it went by.

WJC said:

Omid:

Considering your audience here, I doubt you are going to get much participation. Cloudy Nights would be a little better, but not by much. In addition, it's not safe for postdocs to hang their hats there. Wannabes will come out of the woodwork to set you straight about things they can't even pronounce.

Click to expand...

Thanks for the tips, Bill! Lets wait and see what other forum members' thoughts are. Even if we don't discuss the actual optical design, we can still talk about the implications of binoculars with expanded exit pupil.

For example, have you used binoculars such as Leica 8x50 or Swarovski 8x56 SLC? These have narrow apparent field of view (50 something degrees) but in reality they give a very comfortable and pleasant viewing experience. You can open up the barrels wider than normal and get a beautiful "wide-angle" field of view with both eyes.


Expanding the exit pupil will open up many possibilities.

Omid,

How does this relate, if at all, to the old Galilean binoculars? I know that those are very basic binoculars.

When I was 10 years old my father gave me a cheap, simply made 4x40 Galilean binocular as a birthday present. I had a good time with it for years and I still have it. I took it apart, cleaned the lenses, and even recollimated it by figuring out how to properly relocate the objective lenses when I put it back together, a simple procedure.

In a discussion here years ago I mentioned that it had a very wide exit pupil and I was advised that these binoculars did not, properly speaking, have exit pupils, just like your new telescope.

Bob

perterra said:

It's cool but it's so far over my head I didnt even hear the whoosh when it went by.

Click to expand...

The Plossl EP that causes some amateur astronomers to wet theirt pants was for years simply called what it was--a symmetrical doublet. If you were not not impressed, be happy to stay that way.

From the OTASCO in Pecos, my mom bought me a single EP (built-in) Gilbert telescope (3-inch) in a paper tube. With it I saw: Venus, Jupiter, Mars, and Saturn.

Since then I've learned a lot about optics. Now I see: coma, astigmatism, chromatic aberration, field curvature, etc.

When do you think I was happiest?

Bill

Omid said:

...

In the past few years I have been studying, testing and patenting techniques that can expand the exit pupil of an eyepiece. By this I mean designing an optical device whose exit pupil is larger then the value calculated above. There are several advantages to this design:

a) Large exit pupil makes lateral eye placement uncritical. The larger the exit pupil, the less critical it is to position the eye exactly on the optical axis.

b) Large exit pupil makes longitudinal eye placement uncritical as well. With a large exit pupil, the eye can be before or after the eye relief distance and it will see a reasonable image. The optimal position remains the same (at eye relief) but it is not longer critical for seeing "an" image.

------------

I am creating this thread to open discussion of this topic. I am hoping that it will create awareness and lead to a better understanding of this technique for use in binoculars, spotting scopes and rifle scopes.

Click to expand...

Hi Omid,

Could you share a little more with us about the optics? Is this something incorporated into the basic telescope design, or is it an add-on device? However it's done, is the telescope still afocal, or is the observer looking at an uncoupled projected image?

Sorry, I'm a a bit slow on the uptake.

Ed

WJC said:

The Plossl EP that causes some amateur astronomers to wet theirt pants was for years simply called what it was--a symmetrical doublet. If you were not not impressed, be happy to stay that way.

From the OTASCO in Pecos, my mom bought me a single EP (built-in) Gilbert telescope (3-inch) in a paper tube. With it I saw: Venus, Jupiter, Mars, and Saturn.

Since then I've learned a lot about optics. Now I see: coma, astigmatism, chromatic aberration, field curvature, etc.

When do you think I was happiest?

Bill

Click to expand...

I know the answer, :-O

I like the rifle scope ideas, I can see much potential, even if I dont know what I am seeing.

ceasar said:

Omid,

How does this relate, if at all, to the old Galilean binoculars? I know that those are very basic binoculars.

Bob

Click to expand...

I am focusing on exit pupil expansion for Keplerian (Germans like to call it Fraunhofer) telescopes. In a Galilean telescope the exit pupil (if there is such a thing) is inside the telescope and before the eyepiece.

In a Galilean telescope the entire eyepiece is looks illuminated but the problem with Galilean telescopes is very narrow filed of view. You brought up an interesting point. I will research this further.

elkcub said:

Hi Omid,

Could you share a little more with us about the optics? Is this something incorporated into the basic telescope design, or is it an add-on device? However it's done, is the telescope still afocal, or is the observer looking at an uncoupled projected image?

Sorry, I'm a a bit slow on the uptake.

Ed

Click to expand...

I am thinking of several solutions. In one solution (the one I have posted video demos of), the observer is looking at an uncoupled projected screen. so - as you cleverly guessed- it is no longer an afocal device. See US Patent
8,749,884 for more details.

This is fascinating and congratulations on the work you are doing with this - it probably has many applications. Interested to know if there is any light loss through the screen? And how critical the alignment is to the final image? For example would you envisage the screen being used as eg an add-on (possibly screw or drop-in) filter say before or after an eyepiece?

Cheers, Andrew

to Andrew: Thanks for your positive comments. Yes, there will be light loss at the screen and there is also light that is being diverted to locations other than the observer's pupil. But that's not a problem in many cases. Take a fine 10X25 binoculars and during the day it feels as bright as any 10X50. Light loss might be a problem at night but not during day.


to Ed: Given your marine experience, what are your thoughts on the value of exit pupil expansion (EEP) for marine applications? It should make the binoculars view less susceptible to shake and vibrations.

Beep beep! No more interest in discussing exit pupil expansion in binoculars? OK, how about spotting scopes? How many of you gentlemen (and ladies) have a top quality spotting scope? How many of you find it difficult to position your eye at the eyepiece for extended viewing?

Also, take a look at the company Vision Engineering. They have successfully marketed the same concept for microscopes. Their technology is different than mine though. It is based on diffraction. I use refraction.