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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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What does ASPH mean to you?
Old 02-04-2019   #1
markbakovic
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What does ASPH mean to you?

I don't mean "Is the Leikor Bloktron 42mm 1.3 ASPH a good lens?", I mean what do you understand about "aspheric" *photographic* lenses? What are they for AFAYK? Are there pros and cons? What level of insight would you need to part with 2x the cash? 4x? Shut-up-and-take-my-money... umm... 'times'?
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Old 02-04-2019   #2
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It simply means that one surface of one element doesn’t have a single radius of curvature. As in, it’s not spherical.
As far as better? It usually means the lens designer can replace multiple elements with one element and therefore make a lens simpler and or smaller.
As for your poll, it’s is so misinformed that none of the choices make any sense. Is there a “none of the above”?
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Old 02-04-2019   #3
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Since it is not posted in Leica Lens subforum.
CV ASPH lenses are not x2. 7A 28 f1.4 ASPH is less expensive than non ASPH CV 28 f2. And CV 35 f2 ASPH is less expensive than Biogon 35 f2 non ASPH.

It is shut-up-and-learn-before-posting "times". .
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Old 02-04-2019   #4
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Easier to design and produce lenses?
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Old 02-04-2019   #5
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I didn't see an option that reflects my understanding, either.

To me, the ASPH lens has the potential to perform better at the widest apertures. Stopped down to around f/8, not much difference. Or if there is one, the ASPH may render the image a bit sharper, but the image might look "harsh," less pleasing, depending on what I'm photographing. If I want to shoot at f/2 or f/2.8, I'll likely use a Summicron ASPH. At 5.6 or 8, I might use my Summaron or Zeiss c Biogon, or my non-ASPH Summilux. The latter is, IMHO, useless at f/1.4, but stopped down the images are just fine.

Apart from that, you have to go on a lens-by-lens basis. It's a matter of which lens, not ASPH vs. non-ASPH.
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Old 02-04-2019   #6
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Forgot to mention, my new 35 2.5 ASPH Leica lens cost me less than averagely priced used and worn out Cron. It was one of the reasons I purchased it. .
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Old 02-04-2019   #7
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The very basic Canon and Nikon 18-55 kit lenses both have an aspherical element. Your phone's lens has several. In fact it's rarer for you to see a spherical design than aspherical today, since the later has become so cheap to manufacture.

So the term does not guarantee anything but (mostly) marketing. Which in fact is a Leica (of which the path is followed by CV) specialty. Most of the Japanese manufacturers didn't even bother with it and other terms like FLE (in Nikon's literature, CRC) anymore after the 1980s', during which these technologies became widespread. They've got more posh words to play with now.
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Old 02-04-2019   #8
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To me it means a computer designed lens that has modern characteristics, not necessarily meaning better.

Last edited by kyte : 02-04-2019 at 06:37. Reason: typo
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Old 02-04-2019   #9
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Quote:
Originally Posted by Rob-F View Post
To me, the ASPH lens has the potential to perform better at the widest apertures.
Yes, that plus you tend to swap some barrel distortion for pincushion.
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Old 02-04-2019   #10
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well that was... bracing.

Thank you to the honest respondents to a poll about what camera equipment consumers glean from camera equipment manufacturers' branding.

To the others, thank you for offering your opinions as well.

I look forward to learning more of what readers of the Optics Theory subforum have to say on this topic.

Last edited by markbakovic : 02-04-2019 at 07:18. Reason: *sigh* line breaks
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Old 02-04-2019   #11
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My experience? Aspherical surface usually means a sharper, more contrasty image wide-open, especially with a high-speed lens. Comparing an ancient Canon FD 55/1.2mm with a FD 55/1.2 aspherical wide-open, the difference is dramatic, with the aspherical being much better. Of course many will argue that the signature of the non-aspheric is better. But that’s a personal choice.

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Old 02-04-2019   #12
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If the element count is kept low, an aspherical lens can offer nice correction and wide open performance without that clinical/flat look. I think the Summicron 35/2 ASPH is an example of this, in that it has some 'character' despite the aspherical element.
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Old 02-04-2019   #13
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In some cameras it means a plastic lens. Those I've seen were no better and no worse than normal lenses. OTOH I've been very pleased with "proper" glass ones in various lenses.

I won't mention the technical bit as it's been covered.

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Old 02-04-2019   #14
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ASPH is one of several optical designs purposed to minimize spherical aberration artifacts. The primary symptom is haloing caused by light ray refraction differences between the edges and centers of spherical lens elements. It is impossible to focus the rays to a single point.

The refraction artifacts decrease as aperture decreases since the lens edges become blocked.

Spherical aberration is also associated with focus shift.

Some very fast ASPH lenses have magenta color casts for foreground out of focus objects and green casts for those in the background (spherochromatism). The optical refraction compensation is not the same for all wave lengths. This is different than chromatic aberration.
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Old 02-04-2019   #15
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ASPH ==> extra cost.
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Old 02-04-2019   #16
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It usually means onion-ring bokeh to me.
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Old 02-04-2019   #17
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It usually means expensive, harsh and boring to me.
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Old 02-04-2019   #18
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It means it will be several times the price of the older iteration of the same lense which will henceforth become known as the "non-ASPH" version.
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Old 02-04-2019   #19
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Aspherical lens surfaces are used in all sorts of applications, some expensive, some not. Most are now molded but in the past they were ground which was far more expensive. They have advantages for the design and build of lenses in terms of optical improvements, size, simplicity and so on. The poll is far too simplistic to have any value.
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Old 02-04-2019   #20
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Quote:
Originally Posted by markbakovic View Post
well that was... bracing.

Thank you to the honest respondents to a poll about what camera equipment consumers glean from camera equipment manufacturers' branding.

To the others, thank you for offering your opinions as well.

I look forward to learning more of what readers of the Optics Theory subforum have to say on this topic.
"ASPH" or "Aspherical" on a lens denotes it contains an aspherical surface. You can't just brand a lens as such without an aspherical surface (you can I suppose, but it'd be lying). It used to be a big deal, but now it isn't. You phone most likely has the most aspherical lens you've ever used, yet it doesn't mention it, and doesn't conform with many of the above perceptions of what aspherical surfaces have on image quality.
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Old 02-04-2019   #21
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Meh.
Even some single or doublet molded plastic lenses on simple cameras can have aspheric surfaces. You can tell by the way the surface reflects light.
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Old 02-04-2019   #22
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You should include the choice for "I have no idea really".
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Old 02-04-2019   #23
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I've always enjoyed this "Tessar" from a Nokia phone. Hard to believe it can even make an image, but I guess those aspherical elements do some kind of magic. I wonder if there is even one true spherical surface, even for brief sections of an element-


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Old 02-04-2019   #24
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hmmm, it's an acronym?

Perhaps:

A Serious Photographic Hoax

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Old 02-04-2019   #25
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Not spherical is generally what comes to mind
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Old 02-04-2019   #26
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Ultron 28 1.9 ASPH. Smaller than previously owned 28 2.8 III Elmarit-M. Less expensive as well.
It is not as good as Elmarit-M on darkroom prints, but not flat.
On digital M it is smooth lens. Some are saying it is as good as Summicron 35 f2 ASPH.
Most of my "Hamilton as i know it" color shots were taking with this lens.

Ultron 35 1.7 LTM. This lens was better lens than CS 35 2.5 on prints.
No harsh contrast and it was not flat rending lens at all.
They say VM version of this lens is better comparing to Leica and Zeiss.
I think, it is possible to add focus tab to LTM version. With this it is best 35 RF lens for price and performance. For darkroom prints. IMO.

Nokton 50 1.5 VM. Great lens on prints and on BW digital. More alive lens comparing to sterile Planar ZM, Cron Rigid and IV in BW.

Summarit-M 35 2.5 ASPH - best lens I ever owned and have negatives to print from.
Even better than 35 1.7 Ultron LTM I owned before it. It is not about distortion free and such, which this lens isn't great, but very pleasing rendering of small details, edges and contrast on darkroom prints. It simply gives more on the print, but nothing too sharp.
I'm not using it much on digital M, camera I not using much in general. But it is very good, nothing retro or clinical.
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Old 02-04-2019   #27
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https://en.m.wikipedia.org/wiki/Aspheric_lens
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Old 02-04-2019   #28
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Now, what is APO then, in layman's terms?
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Old 02-04-2019   #29
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Quote:
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Now, what is APO then, in layman's terms?
it makes the red, blue and green lines play real nice with each other.
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Old 02-05-2019   #30
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Quote:
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Now, what is APO then, in layman's terms?
The full term is "apochromatic." It means that the three primary colors, red, green and blue, all come to a focus in the same plane. A non-APO lens might typically bring only two of three primaries (such as blue and green) into sharp focus at the film or sensor plane.
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Old 02-05-2019   #31
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Quote:
Originally Posted by markbakovic View Post
What does ASPH mean to you?
Like Vienna it means nothing to me.

It strictly means that one or more of the lens element surfaces are, as pointed out, made with multiple radii of curvature.

Quote:
Originally Posted by aizan View Post
It usually means onion-ring bokeh to me.
This is annoying. There are methods to polish elements to avoid this, but lens manufacturers typically don't employ them.


This is from a 35 Summilux ASPH (the pre-FLE one). Annoying, it looks weird.

Quote:
Originally Posted by Rob-F View Post
The full term is "apochromatic." It means that the three primary colors, red, green and blue, all come to a focus in the same plane. A non-APO lens might typically bring only two of three primaries (such as blue and green) into sharp focus at the film or sensor plane.
Technically correct, but often used as marketing nonsense, because none of the camera lenses available today are really apochromatic. Microscope and technical lenses are another story.

We should all stop worrying. Go out and take some photos (ASPH lens or not, whatever you like), and show us.

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Old 02-05-2019   #32
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Quote:
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Now, what is APO then, in layman's terms?
In X-ray microscopy (my field) we have two (main) ways to focus X-rays.
The first is a Fresnel Zone Plate, which is a refractive lens. The focal length is a function of the X-ray wavelength, f=(2r*delta(r))/wavelength. So as the wavelength increases, the focal length decreases: It is a chromatic focus.
The second is a Kirkpatrick-Baez mirror pair. The focus here is dependent on the curvature of the mirror, and the wavelength does not figure into the calculations. You can change the wavelength and it does not change the focal length. It is a true achromatic.

In camera lenses, achromatic was first used as an approximation of a true achromatic lens (they converge two wavelengths). Apochromatic was invented for photography (it's not a true scientific word), to distinguish lenses that did a better job than the original achromatic lenses did (they converge three wavelengths). Interestingly, you might think that the three wavelengths would be red, green, and blue, but it doesn't have to be the case, they can include IR or UV (telescopes often include IR for example). Given the looseness the term APO is used in photography, I wouldn't be surprised if this applied to photographic lenses too.
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Old 02-06-2019   #33
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Quote:
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This is annoying. There are methods to polish elements to avoid this, but lens manufacturers typically don't employ them.


This is from a 35 Summilux ASPH (the pre-FLE one). Annoying, it looks weird.
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"?).

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).

Quote:
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Now, what is APO then, in layman's terms?
I see what you did there

To be fair though I don't think you could really get away with designing a lens with, say violet, red and like 740nm or so (which might be reliably picked up by most IR films) brought to the same focus but a huge excursion peaking at 500nm, call it APO and rake in the dollars. But yeah, the similarity in terms of marketing the method rather than the results is... uh... hard to overlook

Once again: I'm not talking about specific lenses which are or are not marketed as ASPH, APO or anything. I'm not insulting your decision to use, or not use any lens so marketed or opinions of same. I'm talking about what, if anything, that marketing implies to you as a consumer. Most of the responses so far have been useful, illustrative and/or entertaining.

Last edited by markbakovic : 02-06-2019 at 02:19. Reason: needed moar APO
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Old 02-06-2019   #34
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Quote:
Originally Posted by markbakovic View Post
I'm talking about what, if anything, that marketing implies to you as a consumer.
The simplest implication is that the design is relatively new and that the lens has been designed with an aspherical surface to improve it in some way (I know that this might mean improve its marketability) so that its performance should be improved or there is another advantage gained (size, weight, production cost, etc.). Like any other 'designation' aspherical/aspheric/asph. is something which appeared as designs took advantage of such surfaces, mostly to differentiate them from older ones, but which has inevitably become something used to try to drive sales. It's interesting that Leica did not immediately use the designation on their more recent Summarit range, almost as though it is now becoming just another tool in their optical designer's options. Perhaps it's now moving away from being a new marketing tool and into the normality of lens design.
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Old 02-06-2019   #35
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My first associative response was to recall the ancient Kilfitt 90mm macro which had an element with two radii.

My second was to recall the last LeicaR 35-70 which had a "secret" aspherical element in the sense that no advertising bothered to mention it.

In the first case concentric rings can be observed, in the second, no particular peculiarities.

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Old 02-06-2019   #36
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Quote:
Originally Posted by Archlich View Post
The very basic Canon and Nikon 18-55 kit lenses both have an aspherical element. Your phone's lens has several. In fact it's rarer for you to see a spherical design than aspherical today, since the later has become so cheap to manufacture.

So the term does not guarantee anything but (mostly) marketing. Which in fact is a Leica (of which the path is followed by CV) specialty. Most of the Japanese manufacturers didn't even bother with it and other terms like FLE (in Nikon's literature, CRC) anymore after the 1980s', during which these technologies became widespread. They've got more posh words to play with now.
That's not true at all. Fujifilm camera lenses have the word "Aspherical" stamped all over them and Canon and Nikon literature prominently highlight the presence of any aspherical elements in their lens designs.
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Old 02-06-2019   #37
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While you are all here can I ask if the advent of optical grade plastic meant that a lot of glass compound lenses were replaced by one plastic lens?

I'm thinking of the triplets that look remarkably like the "4 in 3" glass Tessar.

Regards, David
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Old 02-06-2019   #38
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Quote:
What does ASPH mean to you?
No meaning for me.

Lot of marketing/sales used to justify higher prices.

Maybe the most help with wide angle lenses.

But my Nikkor 20 I bought in 1972 works just fine for me, when I need it, rarely. It’s not ASPH.

Interesting article of injction molded plastic lenses:

https://www.lenseloptics.com/plastic-optics/

Taiwan manufacturer:

https://asia.nikkei.com/Companies/LA...cision-Co.-Ltd
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Old 02-06-2019   #39
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The aspherical lenses I have used (Leica and Voigtlander) have all been very sharp and clinical. Great, I suppose, for color film, but I find them a bit jarring for B&W film.
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Old 02-06-2019   #40
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Quote:
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While you are all here can I ask if the advent of optical grade plastic meant that a lot of glass compound lenses were replaced by one plastic lens?

I'm thinking of the triplets that look remarkably like the "4 in 3" glass Tessar.

Regards, David
It'd still have to be two different plastics to have two different refractive indices, but if, say, the original cemented pair was two glasses with (probably high) dispersion characteristics that together (nearly) cancelled some other part of the system; that might be replaced by a single lens of a similarly dispersive material (which some plastics probably are). After all the Tessar is a modified triplet so you may well be right AFAIK.
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