Where are the aspherics? (1 Viewer)

tenex · Feb 2, 2020

In another thread, Henry Link was just remarking again that to get a crisp view free from simple problems like spherical aberration, he lugs around a 56mm binocular in the daytime. (I've done it myself and see what he means.) Let's turn that into a question: it's 2020. Where are the aspherical binoculars?

Camera lenses have increasingly been incorporating aspherical elements for 25 years now. I recall reading an essay on BVD back then predicting a quantum improvement in bino quality as well. So... what happened? I think there was a Minox(!) some time ago that claimed to have ASPH oculars, and that's about it. Where's the revolution? All but the cheapest binos today flaunt ED glass. Why are top prices still being asked for alpha binos that don't (seem to?) have ASPH elements, and boast instead of improvements so subtle that users struggle to define and debate them?

gunut · Feb 2, 2020

The Japanese made Minox HG had aspheric elements....

Binastro · Feb 2, 2020

There are Docter binoculars with aspheric elements.

Low priced Nikon Porroprism binocular eyepieces have I think aspherical elements.
I don't know which elements.
Possibly plastic aspherics stuck on glass.
When looking across the field the magnification changes slightly in a wave like manner.

Top Sony lenses have genuine worked glass aspherics made by special machinery claimed to be accurate to 1/40th wave.

So I suppose it depends what kind of aspherics and where these elements are.
Also how much improvement is made.

Zeiss were making machine made aspheric elements about 1930.

B.

John A Roberts · Feb 3, 2020

The Pentax Papilios use aspherics (as did some other conventional Pentax roof prism models in their eyepieces)

As many will be aware, the Papilios also use inboard mounted Porro prisms, combined with unique converging objectives
The later ensures that the images for the 2 eyes are coincident when at the very short minimum focus distance (0.5m/ 1.6 ft)

I've attached:
- an image showing the function of an aspheric lens vs a conventional spherical one (I think it's from Pentax about the Papilios, though I can't find the link)

- the specifications for the Papilios from a 2005 catalogue *

- 2 images from a patent showing the objectives, firstly maximally converged for the minimum distance, and then conventionally separated for longer distances

- and the patent

* while the spec's state that each model has an eyepiece of 5 lenses in 5 groups, the patent images seem to show only 4 lenses in 3 groups
EDIT: see Henry's comment in post #5 below: other views in the patent make clear the use of 5 lenses in 4 groups

John

WJC · Feb 3, 2020

John A Roberts said:
The Pentax Papilios use aspherics (as did some other conventional Pentax roof prism models in their eyepieces)

As many will be aware, the Papilios also use inboard mounted Porro prisms, combined with unique converging objectives
The later ensures that the images for the 2 eyes are coincident when at the very short minimum focus distance (0.5m/ 1.6 ft)

I've attached:
- an image showing the function of an aspheric lens vs a conventional spherical one (I think it's from Pentax about the Papilios, though I can't find the link)

- the specifications for the Papilios from a 2005 catalogue *

- 2 images from a patent showing the objectives, firstly maximally converged for the minimum distance, and then conventionally separated for longer distances

- and the patent

* while the spec's state that each model has an eyepiece of 5 lenses in 5 groups, the patent images seem to show only 4 lenses in 3 groups

John

Yet, the wise should beware; aspheric is NOT a magic word. And even salt can look like sugar. There is no doubt we have the technology. That, however, does not mean that technology has been used. Many times, YES. Sometimes, NO. :cat:

Bill

henry link · Feb 3, 2020

John,

Thanks for that. First time I've seen the innards of the Papilio. It looks to me like the 5th eyepiece element is the mildly negative singlet at the bottom of the eyepiece tube, more easily seen in Fig.2 from the patent. That makes only 4 groups rather than 5. Either way, a pretty complex eyepiece for an inexpensive binocular.

Henry

John A Roberts · Feb 3, 2020

Further to gunut's post (#2) re Minox's use of aspheric lenses, see:

- a specification sheet from a 2008 catalogue showing the use of aspherics in both the HG and BD lines, and

- and a labelled cross-section of a BD from the same time (note the simplicity of the eyepiece construction: 3 lenses in 2 groups)

More recent Minox catalogues stress the use of exotic glass rather than aspheric shaped lenses

John

St. Elmo · Feb 3, 2020

The "A" in the Canon 7x42 AWP stood for aspherical.

See: https://www.bhphotovideo.com/c/product/319776-USA/Canon_9671A001_7x42_AWP_Binocular.html

As far as price, I purchased them for my wife for $180 in '08 just as they were being discontinued.

Mike

Canip · Feb 3, 2020

WJC said:
Yet, the wise should beware; aspheric is NOT a magic word. And even salt can look like sugar. There is no doubt we have the technology. That, however, does not mean that technology has been used. Many times, YES. Sometimes, NO. :cat:

Bill

But why is that so? Why is aspheric not a magic word?
If, as tenex mentions, aspheric lenses will not suffer from spherical aberration, what are the drawbacks of the aspherics (you might think price, but that seems not to be the case)?

Troubador · Feb 3, 2020

Canip said:
But why is that so? Why is aspheric not a magic word?
If, as tenex mentions, aspheric lenses will not suffer from spherical aberration, what are the drawbacks of the aspherics (you might think price, but that seems not to be the case)?

The cost of aspherics may well depend on the optical quality that is desired. I have heard of moulded plastics and moulded glass achieving economic prices but poor optical quality. It sounded to me as though true ground-glass aspherics are fearsomely expensive but I can't recall if that was because of the lengthy grinding and finishing or high scrappage rate or a combination of both.

Lee

opisska · Feb 3, 2020

I am not sure I follow the logic of the original post here. Your friend surely doesn't have to carry a large apertute around because of the lack of aspherical optics, mainly because for a given focal length of the objective, all aberrations tend to increase with the aperture, not decrease, so if any telescope would benefit from aspherical elements, it would be the large ones .... If you were complaining that the bins are too long, that I would understand.

Binastro · Feb 3, 2020

In lens making there may be only about 30 master opticians world wide able to make top quality aspherical glass elements to very high standards.

I have heard of some in France, Australia, The Netherlands, Germany, the U.K., Japan and the U.S.
There are undoubtedly others.
It is an art as well as a science.
The lenses sell for £10,000 to £1 million and more.

That is why the Sony aspherics machine is important.
If a machine can replicate a master opticians work, then more large aspherical optics can be made, but still very pricey.
It is not only that the curves must be accurate, but they must be smooth also.
The very top scientific optics still have to be hand made.

With binoculars, the magnification is low, the focal ratio low, and looser standards apply.

For consumer optics in many cases plastic small aspherical elements work well.
They are also cheap.

B.

WJC · Feb 3, 2020

Canip said:
But why is that so? Why is aspheric not a magic word?
If, as tenex mentions, aspheric lenses will not suffer from spherical aberration, what are the drawbacks of the aspherics (you might think price, but that seems not to be the case)?

Please consider the much touted SEA SALT. Except for some created in a lab, what salt does NOT come from the sea—current or dead—or a large lake ... none. Yet, it is much easier to believe misleading advertising than it is to spend 5 minutes researching for yourself.

There are several REAL advantages to using aspheric lenses, weight reduction and better off-axis resolution, for example.

But, consider the attached graphic. All those ads made somebody rich. When Aunt Myrtle sees 100X100 on the back of a binocular, do you think she thinks—or even knows—about its TINY exit pupil or the fact that it doesn’t appear to have a 4-inch aperture? She does not! She sees big numbers that she can afford.

There are prominent companies using aspherics in their binos for excellent results. There are also some companies that will slap “aspheric” in their sales literature when no such lenses exist. :cat:

Bill

jring · Feb 3, 2020

opisska said:
I am not sure I follow the logic of the original post here. Your friend surely doesn't have to carry a large apertute around because of the lack of aspherical optics, mainly because for a given focal length of the objective, all aberrations tend to increase with the aperture, not decrease, so if any telescope would benefit from aspherical elements, it would be the large ones .... If you were complaining that the bins are too long, that I would understand.

Hi,

the logic is quite simple - if you use an 8x56 pair in broad daylight, you will not use its 7mm exit pupil but rather sth like 3mm due to your eyes not being adapted for low light.

This effectively stops down your 56mm instrument into a 24mm one and thus you are not using the far off axis parts of the objective...

Joachim

pbjosh · Feb 3, 2020

Binastro said:
In lens making there may be only about 30 master opticians world wide able to make top quality aspherical glass elements to very high standards.

I have heard of some in France, Australia, The Netherlands, Germany, the U.K., Japan and the U.S.
There are undoubtedly others.
It is an art as well as a science.
The lenses sell for £10,000 to £1 million and more.

That is why the Sony aspherics machine is important.
If a machine can replicate a master opticians work, then more large aspherical optics can be made, but still very pricey.
It is not only that the curves must be accurate, but they must be smooth also.
The very top scientific optics still have to be hand made.

With binoculars, the magnification is low, the focal ratio low, and looser standards apply.

For consumer optics in many cases plastic small aspherical elements work well.
They are also cheap.

B.

This is interesting to me, from an engineering/manufacturing perspective. While I understand completely, and I'm not questioning it at all, I still find it interesting that this cannot be more readily solved with high precision automated manufacturing. Looks like it's time for Google and Youtube and a cup of tea

opisska · Feb 3, 2020

jring said:
Hi,

the logic is quite simple - if you use an 8x56 pair in broad daylight, you will not use its 7mm exit pupil but rather sth like 3mm due to your eyes not being adapted for low light.

This effectively stops down your 56mm instrument into a 24mm one and thus you are not using the far off axis parts of the objective...

Joachim

But what is stopping anyone to produce the same binos but cut down to the effective aperture? Where would be the aspherics needed in that?

Binastro · Feb 3, 2020

Hi pbjosh,

Achim Leistner was pulled out of retirement in Australia to make two perfect spheres out of pure silicon to redefine the kilogram.
It took perhaps a year to make them by hand. Maybe about 2008.
He is originally from Germany and trained at Carl Zeiss Jena.

Horace Dall's skills at hand aspherising may never be achieved by a machine.
Not only do the curves have to be accurate and smooth, but they have to account for slight imperfections in the glass.

There is of course nothing that is truly perfect.

For top scientific laser work, optics are still man made.

There was a nice article about Canon's chief master optician, perhaps in a British photo magazine.
Nikon clearly has similar talent, as do Leica, Zeiss and some others.

When it comes to large telescope mirrors, much is made by machine, but it is humans who supervise the work. It can take years to make one large mirror.

But humans make mistakes, as happened on the Hubble space telescope. A simple test would have shown the error.
If the launch had failed nobody would have known that the optics were faulty.

I suppose the machine itself would need to be perfect and not subject to any wear and tear when making top quality aspherics.

When checking these top optics, two independent careful tests have to be made before passing off the work as ready and completed.

Regards,
B.

tenex · Feb 3, 2020

opisska said:
But what is stopping anyone to produce the same binos but cut down to the effective aperture? Where would be the aspherics needed in that?

We do have smaller binoculars of course, but if you consider how lenses work you will realize that they cannot be "the same cut down", but rather require smaller lenses overall.

Binastro said:
With binoculars, the magnification is low, the focal ratio low, and looser standards apply.

At lower price points I would accept that argument, but not so easily at the alpha level. And I really don't see how aspheric elements can still be so terribly difficult and expensive to make, as they're found today in so many camera lenses.

opisska · Feb 3, 2020

tenex said:
We do have smaller binoculars of course, but if you consider how lenses work you will realize that they cannot be "the same cut down", but rather require smaller lenses overall.

Why couldn't they? If you are not using the non-axial beams, then just don't put that part of the lenses in. Voila, a lens with a smaller relative aperture, thus less aberrations. This is literally how astronomical refractors were made before the advent of unusual glass types - long f-ratios for lower aberrations.

This doesn't work well for photography, where the f-ratio matters, but for visual observation this is perfectly working, because you just have the appropriate eyepiece to get the same magnification. Mind you, you already have it in the binocular in question anyway ...

Exit pupil = entrance pupil/magnification, so you get the same effect by making you eye smaller as by making the objective lens smaller.

Binastro · Feb 3, 2020

What doesn't seem to be understood is that the 8x56 has an objective focal length of maybe 210mm.

Cutting the aperture down to 24mm with a 3mm eye pupil, the focal length is still 210mm but the focal ratio is now f/8.75 instead of f/3.75.

Observers would not want a 24mm binocular to be as long as the 8x56.
But at f/8.75 the performance would be good.

As to why Alpha binoculars don't have more aspherics, it is probably economics. A similar performance might be achieved with spherical elements but more of them, than having fewer elements including aspherics.

If it made economic sense then aspherics would be used.

I think that some high end military binoculars were aspherised by hand.

B.

Where are the aspherics? (1 Viewer)

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