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Optics Theory - This forum is aimed towards the TECHNICAL side of photographic OPTICS THEORY. There will be some overlap by camera/manufacturer, but this forum is for the heavy duty tech discussions. This is NOT the place to discuss a specific lens or lens line, do that in the appropriate forum. This is the forum to discuss optics or lenses in general, to learn about the tech behind the lenses and images. IF you have a question about a specific lens, post it in the forum about that type of camera, NOT HERE.

View Poll Results: What's in an ASPH?
It's a better type of lens 8 13.79%
Marketing B.S. only 5 8.62%
100% aspheric lens elements, no more spherical aberration or distortion for me! 7 12.07%
a small design tweak that *might* give a sharper image with less elements 38 65.52%
Voters: 58. You may not vote on this poll

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Old 02-06-2019   #41
Freakscene
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Quote:
Originally Posted by markbakovic View Post
that looks a bit like cavity resonance to me a la Fabry-Perot, like a surface pair is locally close to plane parallel. If so that might be unavoidable with the geometry in question. (I say this in part because the image looks near-monochromatic: does it still do it with white, with no colour fringing "in the onion rings"?).
It is not due to the geometry of the lens. They are the result of marks on the aspherical element from the manufacturing process. They still appear in monochrome.

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Originally Posted by markbakovic View Post
If you mean the method of "machining" aspheric surfaces with a diamond stylus and then not smoothing the grooves, I guess this is one way to avoid too much cost increase: if you look at optic catalogues and the same-size, same-glass, same-EFL, same-surface tolerance precision asphere is 2-5x the price of the corresponding spherical item that input cost has to either be passed on to the consumer or reduced somehow. I guess it boils down to microfacets left on glass or moulded plastic (at least index matched caps) or less money spent elsewhere (or price hike).
Most camera aspherical lens elements are manufactured by pressing hot liquid glass against a mould. The mould is a machined metal template with a curvature in the negative of the lens surface. The concentric patterns are traces of the turning process with which the moulds are manufactured. There are ways to both polish the mould and the elements to avoid this, but manufacturers typically don't employ them. The $US8k Leica 50mm Summicron ASPH APO has these concentric rings in the bokeh, and at that price point I'd have thought they would polish the mould better.

Marty
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Old 04-03-2019   #42
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Quote:
Originally Posted by aizan View Post
It usually means onion-ring bokeh to me.
I understand all the responses, yet experience has meant this is still the first thing that I think of when I see ďaspheric elementsĒ mentioned in a lens design. For me, it means bottom of the 9th, two out, two strikes, behind 8 to nothing, facing Mariano Rivera.
Game isnít over, but I have a bad feeling.
Yeah, Iím unapologetically ďone of thoseĒ.
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Old 04-03-2019   #43
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Found this article at B&H:

https://www.bhphotovideo.com/explora...ur-photographs
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Old 04-03-2019   #44
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Originally Posted by Freakscene View Post
There are ways to both polish the mould and the elements to avoid this, but manufacturers typically don't employ them.

Marty
Marty,

Are there any lenses with aspheric elements which donít exhibit onion ring out of focus highlights, that you know of?

I always thought it was just due to the asph, somehow, so I learned something today. Thanks for that!

Larry
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Old 04-03-2019   #45
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Quote:
Originally Posted by Larry Cloetta View Post
Marty,

Are there any lenses with aspheric elements which donít exhibit onion ring out of focus highlights, that you know of?

I always thought it was just due to the asph, somehow, so I learned something today. Thanks for that!

Larry
In camera lenses, the Pentax 43mm f1.9 doesnít do it, in my experience. That doesnít mean it canít.

Hoya, who owns Pentax, holds a lot of patents about production of aspheres.

Marty
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Old 04-03-2019   #46
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If I am being cynical what it means in commercial terms is "the next big reason" to buy the next model of any given lens. (Equipment makers must keep us buying to stay in business - what we bought yesterday is irrelevant - the only thing that matters is what we will buy tomorrow and they must keep innovating to keep this cycle happening). But to be ultra fair I should also add that it means (for complex modern DSLR zooms etc especially) the ability to make new lens types that are difficult or impossible to make otherwise and, given modern aspherical lens molding technology, to make these lenses relatively inexpensively, physically smaller and much lighter. It would be unfair not to acknowledge that using aspherical elements can mean using less elements in a lens design and this in turn can be used to make those lenses smaller, lighter and cheaper to build especially when combined with modern manufacturing materials (plastics) and computer aided manufacturing.

For top end hand built rangefinder type primes more often than not though, it also unfortunately means more expensive and eye wateringly clinical and sharp lenses - with pretty crappy bokeh. I do not know if using aspherics necessarily means less attractive bokeh or it is just that bokeh is being neglected in favour of other characteristics (sharpness) but they could get around to fixing that eventually if they are motivated to do so by buyer resistance. Maybe someone with more optical theory than I (and that's not hard given my lack of knowledge in this field :^) ) can advise on this.
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Old 04-03-2019   #47
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Optical engineers when designing a lens decide it's appropriate to include an aspherical element. I can care less about this as a consumer any more than an electronic device has this component or that. I once read up on what they did, why they're used but I forgot. Didn't revisit because I don't care.

At one time ASPH elements were included only in expensive lenses because they were difficult and costly to produce. However, for some time they have been produced (apparently) cheaply with optical grade resin cemented to the element not the whole element ground to an aspherical shape. The 28-80/3.3-5.6 plastic fantastic Nikon kit lens I snatched used for $30 boasts an aspherical element. It's an okay lens for what it is. No complaints. I trust it benefits from the aspherical element. It does only have six elements.

I trust that the lens engineers know what they're doing. ASPH is they type of fancy sounding spec that gets put in the "plus" column despite the average consumer not knowing what it is/does which as they proliferate loses its marketing value as a fancy spec. term. Like the names the marketing people would give to lens coatings.

There is also asph (resin) and Asph (ground glass). But that's a hard concept to marketeer.
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Old 04-03-2019   #48
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Quote:
Originally Posted by Freakscene View Post
In camera lenses, the Pentax 43mm f1.9 doesnít do it, in my experience. That doesnít mean it canít.

Hoya, who owns Pentax, holds a lot of patents about production of aspheres.

Marty
Thanks. Again.
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Old 04-03-2019   #49
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ASPH? Thomeone has a listhp.
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Old 04-06-2019   #50
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Something I can't afford generally!
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Old 04-06-2019   #51
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It means I can't afford it.
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Old 04-07-2019   #52
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I hate most asperics as backgrounds (bokeh) look like broken glass shards..
The higher price not justified by tiny increases of sharpness and contrast.
I tested 2 ASPH lenses "said" to be Apochromatic as well.
A simple test (Erwin Puts agreed with my findings) proved they were not the APOCH.
I have a Collapsible-Summicron 50mm that i use (pristine elements). (1954~55).
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Old 04-07-2019   #53
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ASPH. Without the H it is the snake that strikes at the breast. Either the price or the lack of difference, or the cold high contrast - any one of these - gives you a heart attack. Or you can't tell the difference for the price, which is the same pain or worse. And it doesn't help that we sometimes learn that a lens or line of lenses was actually also ASPH e.g the modern Summarits. And they were actually f2.4 not f2.5 all along. The other day I read that something was also APO too. My little Elmar f3.5, pretty sharp, seems uninterested in all of this.
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Old 06-01-2019   #54
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Quote:
Originally Posted by Larry Cloetta View Post
Are there any lenses with aspheric elements which donít exhibit onion ring out of focus highlights, that you know of?
The newest Sony lenses are made using improved polishing techniques for aspherical elements, at least in part to avoid onion ring bokeh.

https://www.dpreview.com/sample-gall...ery/4645480957

Marty
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Old 06-05-2019   #55
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Quote:
Originally Posted by Freakscene View Post
It is not due to the geometry of the lens. They are the result of marks on the aspherical element from the manufacturing process. They still appear in monochrome.



Most camera aspherical lens elements are manufactured by pressing hot liquid glass against a mould. The mould is a machined metal template with a curvature in the negative of the lens surface. The concentric patterns are traces of the turning process with which the moulds are manufactured. There are ways to both polish the mould and the elements to avoid this, but manufacturers typically don't employ them. The $US8k Leica 50mm Summicron ASPH APO has these concentric rings in the bokeh, and at that price point I'd have thought they would polish the mould better.

Marty
Thanks for explaining; I didn't know that was the cause of those OOF rings..

For what it's worth, I had both the Nikon 50/1.8 AF-D and G versions at the same time for a while. The latter has more elements, one of which is aspherical. In the end, I preferred the images of the simpler AF-D version and sold the G.
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Old 06-05-2019   #56
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Quote:
Originally Posted by Rayt View Post
Easier to design and produce lenses?
Ray,

The first ASPH lenses required hand grinding and were not so easy to make.

They offered a complexity.

I would say they are more complex and not as simple a lens to make.

Some early examples of ASPH that were hand ground: Noct-Nikkor 58/1.2; Noctilux F1.2.

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Old 06-05-2019   #57
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ASPH to me means a highly corrected lens with enhanced sharpness.

Sometimes though the spillover can be harshness, unsmooth OOF, and ugly bokeh.

Cal
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Old 06-05-2019   #58
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I thought "ASPH" meant "aspherical".

Silly me.
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