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

[pat mitchel]

Hello; There a poster on cloudy nights forums/ binoculars that hs a problem selecting binos- he has optical blackouts with multiple binoculars *(typically with the eyecups extended full height) that apparently only happen in binos that have a wider AFOV than 60 degrees. Not having experienced anything remotely like that, my simple suggestion was that for whatever reason, he might need more eye relief. While that moderated the problem (at least in the case of the 8x42 vortex DB) it still remains. Anyone have an explanation as to what is happening that I might be able to relay to the poster with the problem. Thanks, Pat

 

[WJC]

Does the OP need high relief, since the ER may be restricted and the eye cups may not be long enough fully extended.

In the PUBLISHED photo, I talk of where the IMAGE IS FORMED IN SPACE! That is Bull. It is the eye point. 'scuse me ......!

 

[pat mitchel]

the first bino he tried was a vortex DB 8x42 and with the eyecups all the way up he had nothing but blackouts - intermittent but pretty much killed the continuity of the view. He tried athlon midas ( I think they were 8x42 (8.2 fov but might have been 10x50 6.5 fov- he wasn't too specific) and they were equally bad. For some reason a celestron 8x56 skymaster (5.8 FOV) was tried and although the view was poor in comparison the 2 roofs regarding sharpness and contrast, there was no problem with blackouts. There's a wealth of narrower binos (like pentax) that might offer decent consistent views . I think the skymaster has 18mm ER with twist up cups- again with the eyecups up all the way. He's at a loss to explain the situation. Regards, Pat

 

[WJC]

the first bino he tried was a vortex DB 8x42 and with the eyecups all the way up he had nothing but blackouts - intermittent but pretty much killed the continuity of the view. He tried athlon midas ( I think they were 8x42 (8.2 fov but might have been 10x50 6.5 fov- he wasn't too specific) and they were equally bad. For some reason a celestron 8x56 skymaster (5.8 FOV) was tried and although the view was poor in comparison the 2 roofs regarding sharpness and contrast, there was no problem with blackouts. There's a wealth of narrower binos (like pentax) that might offer decent consistent views . I think the skymaster has 18mm ER with twist up cups- again with the eyecups up all the way. He's at a loss to explain the situation. Regards, Pat

Hi, Pat:

Check to see how long he has been on the forum. I mean NO OFFENSE to this fellow. However, I have seen many posters with only a few binocular credits to their name who find any number of anomalies that experienced observers have never seen. And so it goes ... as it always has.

 

[Trinovid]

Hopefully someone will offer help eventually so that the poor chap can start enjoying his binoculars.

 

[PeterPS]

First he should carefully adjust the distance between eyecups (especially if he has a narrow/wide IPD). Then if he still has blackout issues with the eyecups fully extended, he should let the binos "float" in front of his eyes, at least he should avoid sqeeezing them in his eye sockets (he probably has shallow sockets, and the binos he tried have a lot of ER---for people wearing eyeglasses---and their eyecups do not extend enough for him).

 

[pat mitchel]

I mentioned the IPD and he stated it was 67mm as checked by the smartphone app. I also suggested using the ballcap/billed visor where you grasp the binos out a bit off the face with the bill simultaneously. Not being there, seeing what he's doing (although he is a photographer so the eye/instrument steadiness should be there) creates a situation where you offer possible remedies and then ask if he tried it.

 

[tenex]

Peter is right, if a blackout problem isn't IPD it's probably too much eye relief for the eyecup depth, a problem I often have these days. Since holding bins out further is very awkward, it's better to get deeper eyecups if possible. (Even a couple of mm can help; I have eyecups from the 8x on my SLC 10x56 for this reason.)

But it's also possible that he just keeps looking too far away from the center toward the edge of the field, which most designs don't tolerate well. (And this might be more likely to happen with a wider AFOV, as he mentioned.) In this case he needs to move the binocular more instead of his eyes.

 

[Ted Y.]

Hi, Pat:

Check to see how long he has been on the forum. I mean NO OFFENSE to this fellow. However, I have seen many posters with only a few binocular credits to their name who find any number of anomalies that experienced observers have never seen. And so it goes ... as it always has.

As for any tool, one must know how to use it and how not to use it. And no one can say RTFM, because such thing as a manual does not exist for binoculars.

 

[kimmik]

There is something inherently difficult with wide angle optics.

The bare naked eye has an infinite “exit pupil” to look through, and thus it is normal to have no black.

With a telescope/bino, you’re suddenly at millimeters of exit pupil sweetspot to look at as big an AFOV as you can.

Especially if the bino has excellent edge to edge image quality, you want to scan around instead of keeping your pupil perfectly centered all the time.

So the solution is exit pupil. The wider the AFOV, the bigger the exit pupil you want in order to reduce blackouts. If you thought 4mm was enough for 60degrees, perhaps you need 5mm for 70degrees, or more.

Another solution is to increase your entrance pupil size (ie your eye’s pupil), but thats kind of limited to dark places and works better in younger eyes.

If you absolutely hate blackout, try these: 6x32, 7x42, 7x50, 8x56, 50degree AFOV. And Avoid flat field designs which encourage eye roaming. Plenty of options available but you cant have your physics cake and eat it too. Find a compromise you can accept.

 

[elkcub]

Hello; There a poster on cloudy nights forums/ binoculars that hs a problem selecting binos- he has optical blackouts with multiple binoculars *(typically with the eyecups extended full height) that apparently only happen in binos that have a wider AFOV than 60 degrees. Not having experienced anything remotely like that, my simple suggestion was that for whatever reason, he might need more eye relief. While that moderated the problem (at least in the case of the 8x42 vortex DB) it still remains. Anyone have an explanation as to what is happening that I might be able to relay to the poster with the problem. Thanks, Pat

Pat,
Please read the section entitled "Spherical Aberration of the Exit Pupil" at the end of this article.

"Spherical aberration of the exit pupil almost exclusively afflicts eyepiece designs with fields larger than 60° — wide angle or super wide angle eyepieces. Given the limitations of the eye, and the fact that spherical aberration will black out a large part of the eyepiece field, rendering it useless, it is more practical to use eyepieces that present the true field of view as an apparent field no wider than 60°, then choose an eyepiece focal length (magnification) that fits an extended object entirely within the eyepiece's true field of view."​

Hope it helps. What little technical interest I had in the subject, however, has been mercifully forgotten long ago.
Ed

 

[kimmik]

Saotep makes a difference too though the NL eyepiece has minimal when i tested it.

 

[Omid]

Ed (Elkcub) gave the accurate technical answer in post # 11. I will add one more point:

The eye does not see a wide angle field of view all at once as in a wide-angle camera. It rotates and scans the field (the sharp field of view of human eye is about 1 degree). The entrance pupil of the eye is located a few millimeters forward of the center of rotation of the eye (exact position depends on accommodation). When the eye rotates, it entrance pupil sweeps around and can easily move outside the small exit pupil of the eyepiece.

A wide AFOV binocular requires long eye relief and wide exit pupil so that the "center of rotation" of the eye can be positioned at the exit pupil. This will minimize (but not eliminate) the chance of the entrance pupil cutting off the field beams coming out of the eyepiece during eye rotation.

-Omid

 

[kimmik]

Ed (Elkcub) gave the accurate technical answer in post # 11. I will add one more point:

The eye does not see a wide angle field of view all at once as in a wide-angle camera. It rotates and scans the field (the sharp field of view of human eye is about 1 degree). The entrance pupil of the eye is located a few millimeters forward of the center of rotation of the eye (exact position depends on accommodation). When the eye rotates, it entrance pupil sweeps around and can easily move outside the small exit pupil of the eyepiece.

A wide AFOV binocular requires long eye relief and wide exit pupil so that the "center of rotation" of the eye can be positioned at the exit pupil. This will minimize (but not eliminate) the chance of the entrance pupil cutting off the field beams coming out of the eyepiece during eye rotation.

-Omid

So just to confirm, you think no saotep = no blackout?

 

[Hermann]

A wide AFOV binocular requires long eye relief and wide exit pupil so that the "center of rotation" of the eye can be positioned at the exit pupil. This will minimize (but not eliminate) the chance of the entrance pupil cutting off the field beams coming out of the eyepiece during eye rotation.

This may be so. However, I never get any blackouts with the Zeiss West porros 8x30 (150m/1000m) and the 10x50 (130m/1000m) with their Erfle eyepieces. And the Erfles have very short eye relief, something like 11 mm. No large exit pupils either.

Hermann

 

[Binocollector]

This may be so. However, I never get any blackouts with the Zeiss West porros 8x30 (150m/1000m) and the 10x50 (130m/1000m) with their Erfle eyepieces.

Just wanted to mention the same thing about my vintage wide angle Japanese porros from the 70's. They probably have the same type of eyepieces and black-outs are much less than on any modern day roof prism bino with long eye-relief.

 

[kimmik]

This may be so. However, I never get any blackouts with the Zeiss West porros 8x30 (150m/1000m) and the 10x50 (130m/1000m) with their Erfle eyepieces. And the Erfles have very short eye relief, something like 11 mm. No large exit pupils either.

Hermann

8x30 150m is pretty similar to the nikon m7 8x30 145m, and 10x50 130m is similar to nl 8x42 (5mm ep 70deg afov).

Those are my two favorite formats!

 

[Omid]

So just to confirm, you think no saotep = no blackout?

Spherical aberration of the exit pupil is the main cause. Yet, another cause is vignetting of the field beams coming from the edges of field of view. Up to 50% vignetting is considered OK in designing visual instruments: your binoculus might create a nice 5mm circular exit pupil for the central beam, but not for the exit beams coming out at 20-to-30-degree field angle. The field exit beams in many binoculars look like moon crescents. This is caused by under-sized prisms used to same weight and bulk.

-Omid

 

[kimmik]

I disagree but to each their own. As I said, NL eyepieces have negligible saotep.

 

[Omid]

I disagree but to each their own. As I said, NL eyepieces have negligible saotep.

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