blackouts at AFOV of greater than 60 degrees- why (1 Viewer)

[kimmik]

I didn't say anything about Swarovski NL binoculars; what I mentioned are general facts of visual optics

based on your theory though, the NL will have no blackouts.

 

[Omid]

based on your theory though, the NL will have no blackouts.

As I said, I have no opinion on whether NL binoculars have black-out problems or not. I don't own these models and I don't follow their reviews or user opinions. So, have you experienced blackouts while looking through Swarovski NL binoculars? And then you have tested their eyepieces for spherical aberration of the exit pupil?

From your comments I guess the answer to my first question is yes and to the second is no. From which you then conclude that my explanation about what causes black out is not adequate.

How did you measure the spherical aberration of the exit pupil of your NL binoculars? I am curious to know if there is an easy test to measure spherical aberration of the exit pupil.

Thanks,
Omid

 

[kimmik]

You have understood the dilemma perfectly

Yes I experienced increased blackouts with the NL 10x32, which I really wanted to like but couldn’t. less so on the NL 10x42 and even less so on 8x42. Not related to image shake.

As for how to test saotep, you can start by measuring eye relief. More than one way to skin the cat, my way was using a white phone screen as light source at the objective, then project the exit pupil from the eyepiece, onto the wall and measuring the distance.

Then the next step is to block the central 80% of the eyepiece and repeat measurement. Saotep would manifest as shorter eye relief on the second measurement, and a fuzzy exit pupil (spherically aberrated) on the first test.

 

[Omid]

You have understood the dilemma perfectly

Yes I experienced increased blackouts with the NL 10x32, which I really wanted to like but couldn’t. less so on the NL 10x42 and even less so on 8x42. Not related to image shake.

As for how to test saotep, you can start by measuring eye relief. More than one way to skin the cat, my way was using a white phone screen as light source at the objective, then project the exit pupil from the eyepiece, onto the wall and measuring the distance.

Then the next step is to block the central 80% of the eyepiece and repeat measurement. Saotep would manifest as shorter eye relief on the second measurement, and a fuzzy exit pupil (spherically aberrated) on the first test.

Hi Kimmik,

Thank you for the clarification. OK, so you experienced blackouts on the smaller size NL models. Your experience could be due to the small exit pupil size and, in addition, spherical aberration of the exit pupil and, further due to vignetting of the field rays.

I am afraid your clever experiment does not measure spherical aberration of the exit pupil. What you are doing would be relevant to measuring spherical aberration of a lens when forming an image. When a lens forms an image, often the beams that are refracted by the peripheral part don't converge to the same focal position as the paraxial rays. This is called spherical aberration of the lens.

Spherical aberration of the exit pupil is a different concept. It has nothing to do with the specific area of the objective lens used by an entering beam; it is related to the angle of the beams entering the system. You have to feed the system under test with a collimated beam not parallel with its optical axis. Then increase the entrance angle of the entering beam and see if the exit beams all cross the optical axis at the same point behind the eyepiece.

-Omid

PS. I admit that the term "spherical aberration of exit pupil" can be misleading. They should have picked a better name for this phenomenon, something like exit pupil inconsistency or exit pupil shift with angle of view. In many practical visual systems, both the exit pupil shape and position depend on the angle of view.

 

[Vespobuteo]

You have understood the dilemma perfectly

Yes I experienced increased blackouts with the NL 10x32, which I really wanted to like but couldn’t. less so on the NL 10x42 and even less so on 8x42. Not related to image shake.

As for how to test saotep, you can start by measuring eye relief. More than one way to skin the cat, my way was using a white phone screen as light source at the objective, then project the exit pupil from the eyepiece, onto the wall and measuring the distance.

Then the next step is to block the central 80% of the eyepiece and repeat measurement. Saotep would manifest as shorter eye relief on the second measurement, and a fuzzy exit pupil (spherically aberrated) on the first test.

For how long did you use them?

Had blackouts with my Swaro scope/EP (AFOV 65°) when starting using it but when I got used to the EP it's no longer a problem and I don't see any at all.

I think it's learning curve for the hand/brain/eye, and perhaps adjusting eye cups and IPD.

Longer ER than you might be used to is often a bigger problem than short in these cases.

A smaller exit pupil won't help either obviously as alignment will be more difficult.

 

[kimmik]

Hi Omid, I’m afraid you are mistaken. But I won’t waste more of your time getting further into this topic.

 

[Vespobuteo]

Hi Omid, I’m afraid you are mistaken. But I won’t waste more of your time getting further into this topic.

I think "spherical aberration" in the EP was more of an issue in older binoculars with simpler eye pieces.

Modern "high end" eye pieces have a much better "eye box", so it's more about adapting to correct eye relief etc.

But I could be misstaken....

 

[kimmik]

I think "spherical aberration" in the EP was more of an issue in older binoculars with simpler eye pieces.

Modern "high end" eye pieces have a much better "eye box", so it's more about adapting to correct eye relief etc.

But I could be misstaken....

Agree. Larger exit pupil further widens the “eye box”, more important with wide angle binos.

 

[Omid]

Hi Omid, I’m afraid you are mistaken. But I won’t waste more of your time getting further into this topic.

No problem, and you are welcome

 

[kimmik]

Since there are those claiming wider angle eyepiece = more spherical aberration of the exit pupil (SAEP/SAOTEP), I have measured the SAEP of the EL and NL eyepieces, specifically EL 8x32 and NL 8x42.

This method using phone camera is well documented on cloudynights forum. The darker the peripheral ring, the greater the SAEP.

The NL despite the substantially wider AFOV of 69deg vs 61deg, has less SAEP.

EL

NL

 

[kimmik]

And this is a pentax bino with about 0 SAEP tested under the same methodology, For comparison to the above two. Notice the dark ring is completely at the periphery, with no bright outer ring.

Pentax