Binocular Evolution II: Curvature and Distortion (1 Viewer)

[tenex]

No, overall its compound distortion that is rather seldom used rather than seldom avoided and cost has nothing to do with it. The designers of other flat field "optical devices", meaning other flat field eyepieces, have simply chosen other distortion profiles. That's not necessarily doing better, it's just making a different choice. My guess is that compound mustache distortion was chosen by Swarovski and then Zeiss simply to avoid the appearance of too much old fashioned pincushion distortion in the image by taking most of it away near the edge of the field. As Holger mentioned, the guys at Swarovski were apparently unaware that low pincushion at the field edge would distort shapes there in a way that leads to the globe effect when panning.

So you're imagining that compound distortion was initially a deliberate choice for its own sake, rather than a byproduct of field-flattening which was eventually got rid of to the extent possible. That's actually not what Holger said above, so I hope he can comment on that.

 

[Holger Merlitz]

So you're imagining that compound distortion was initially a deliberate choice for its own sake, rather than a byproduct of field-flattening which was eventually got rid of to the extent possible. That's actually not what Holger said above, so I hope he can comment on that.

Of course we don't know about their intentions, since they won't tell us, but we know about the outcomes and consequences. I believe that the combination of a wide angle, a perfect edge sharpness and size/weight limitations of the eyepiece didn't leave the optical designer much freedom to choose the distortion curve. He had to balance all aberrations, and edge-sharpness had highest priority. This is a fact and was also expressed so by Swaro: They wanted an edge sharpness that was superior to anything else on the market. The designer then put 100% weight onto that task in his design software and got a solution. He then found that the image was actually not fully flat but had a little bump about 80% toward the edge. Beyond that, it was pushed back onto the image plane to get that perfect edge sharpness. It looks like a brutal, forceful act to hammer the focus, which was about to leave the image plane (as it would naturally do far off the center), back in place. The bump was sufficiently flat, 1/2 diopter or so, and it was believed to be invisible to the eye. Similarly, the distortion curve showed such an unusual behavior. They saw it and probably thought 'look at that, there is some pincushion in the center region and no further distortion out there at the edges, so it is a win-win with no globe effect and straight lines'. They could have altered that distortion curve, but not without compromising edge sharpness. Or they could have added another lens-element to have some more degrees of freedom to do that job, but that would have been costly and increasing the size of the eyepiece. But first of all, they didn't know about the side effects. So they left it in place.

Later on, that strange panning behavior was found. Even that little bump in the image plane did not remain unnoticed: When panning over a structured surface, it emerged as a ringlike soft region, named here 'the Absam ring'. Human vision is great at detecting unnatural conditions in particular with dynamical images, since a powerful image processing takes place in the visual cortex that rings the alarm bells whenever something appears to be unusual - a protection mechanism, implemented during millions of years of tough fight for survival. Just one example: Sea sickness causes nausea and is actually a protection against food poisoning. Many toxins affect the nervous system and also the visual perception. Once strange movements are perceived (on a rocking boat or vehicle), the first reflex is to empty the stomach and to get rid of possibly rotten or poisoned food. Another example: Preditors rarely attempt a frontal attack. They sneak up from behind or the side. Nerve cells in our retina are, far off-center, connected to form receptive fields which are designed to detect movements. They actually do some kind of image preprocessing right below the retina to immediately inform the brain if something potentially dangerous is going on. Visual optical instruments with very wide subjective angles do increasingly involve these peripheral areas of the retina, which makes the experience of panning particularly impressive to the viewer. Much can go wrong here if the distortion curve shows anomalies. Remember what Nikon designer Tomita said about the difficulties when designing the 10x50 WX with 85° subjective angle, finding problems only in real life applications after the prototypes were out. The optical design software simply doesn't analyze moving images. I have once suggested Swaro to use these virtual reality sets, to plug in via software the optical characteristics of their new designs and to let test persons judge their behavior while panning over virtual landscapes. This would be no problem with the computational power of modern graphic cards, and it would help eliminating problems in a rather early stage of product design. I don't think that this idea has been followed up so far.

Cheers,
Holger

 

[kimmik]

While we are doing a bit of future gazing, also consider the incredible march of integrated cameras in mobile devices aka camera phone, which has become the dominant source of photography in day to day living and will be for all future generations. Therefore binoculars are not just telescope for eyes, but telescopes for phone-eyes, something I have done regularly since 2015. A flattened binocular undoubtedly produces better pictures when used with camera.

Also, I got very car sick as a child, but don't even notice it these days. The question is who wants what tradeoff for what benefit.

 

[Holger Merlitz]

This is true: Eyes and cameras are very different machines, and visual perception is flexible and can be trained. For some, a globe effect may not be noticed any more after several months of regular observations with the same binocular.

Cheers,
Holger

 

[MiddleRiver]

I've owned a string of Leica binos over the years and recently purchased the SFL8x40's. At first, the rolling-ball bothered me (even tho it's said to be minimal in the SFL's) and for a bit I thought it might be a deal-breaker. It just didn't look natural, and for the first time I realized that the 'leica' strategy made sense (to me). I did decide to take them on a month long trip, and I found that it became less noticeable with use, tho it sometimes becomes noticeable when panning a tree-line. So, for me at least, the flat-field craze is meaningless and in fact i prefer an Ultravid type view. I DO admit I've become a fan of a wider view, but curvature and edge fall-off don't detract from my viewing experience. I realize if I was tripod mounted and scanning night sky I might think differently.

 

[Troubador]

I realize if I was tripod mounted and scanning night sky or western plains for game, I might think differently.

I don't recommend you getting yourself tripod-mounted, it could be quite uncomfortable .

Lee

PS Birforum is a hunting-free zone.

 

[tenex]

... visual perception is flexible and can be trained. For some, a globe effect may not be noticed any more after several months of regular observations with the same binocular.

I suspect that something similar could also be said for jitter due to magnification (which of course is present to some degree in any binocular) if people were to practice more with 10x (or 12x, even 15x) instruments they think they "just can't use".

Thank you for your comments on distortion. I've been curious about this for a long time.

 

[Holger Merlitz]

Allow me to add that in a recent Zeiss patent WO2022034231A2 I have found a confirmation that Zeiss is indeed optimizing some of their products with the help of my model of the globe effect (see citation below, which in the German PDF file appears on p. 71). Then, perhaps, the choices of distortion values in recently introduced binoculars seem to be no accident but (at least in parts) a result of my research efforts

Cheers,
Holger

With regard to the intended use in binoculars, the eyepiece 6 can have a pincushion distortion of 5.3% at the edge of the field of view. This value of the distortion and the progression over the image field are selected in such a way that the "globe effect" that occurs when panning sideways (cf. publication by H. Merlitz, "Distortion of binoculars revisited: Does the sweet spot exist?", J . Opt. Soc. Am. A/Vol. 27, No. 1/January 2010) is minimized. The "globe effect" is a well-known and empirically well-confirmed effect, but its exact physiological and perceptual-psychological causes are still being discussed, in which the visual impression of the observer when panning binoculars to the side, such as when "matching". “ of the starry sky, would perform a kind of rolling motion on a spherical surface. Compliance with the so-called Merlitz condition, which is discussed in the above publication, with an empirically determined Merlitz parameter of k=0.7, which is also discussed in the above publication, results in the specified field of view of +/-30° to a used pincushion distortion of 5.3% at the edge of the field of view. This is maintained by the embodiment of the further optical system 7 according to the invention discussed here. In this way, the Globus effect is avoided as best as possible.

 

[Canip]

Late, but well deserved appreciation for your great work, dear Holger! 👍👋
So you are now sort of an „honorary Zeiss employee“? 🧐

 

[Holger Merlitz]

Thank you so much, Christophe, this means a lot to me! Having a consistent model for some phenomenon is a fine thing, but having it applied to a real life product is a considerable step forwards. As far as I know, Zeiss is the first manufacturer who has publicly acknowledged this study. Honorary employee? Haha, more 'honorary' than 'employee', there is no money flow

Cheers,
Holger

 

[Canip]

No money, of course, that‘s what I meant by „honorary“ …
Remember how we renamed the new Trinovid „Retrovid“? Why can’t we call the distortion profile in the SFL „Merlitz Distortion“ ?😁

 

[Holger Merlitz]

No money, of course, that‘s what I meant by „honorary“ …
Remember how we renamed the new Trinovid „Retrovid“? Why can’t we call the distortion profile in the SFL „Merlitz Distortion“ ?😁

Oh well, let's first see how the distortion characteristics of the 30mm versions turn out to behave, otherwise ...

Cheers,
Holger