Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the difference?

[pkr1979]

Hello folks,

Whats the practical differences of Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses?

Does Apo and ED serve the same purpose regarding chromatic aberration?

While aspherical lenses has better image sharpnes across?

Cheers
Peter

[Dan Fromm]

Sigh. Another closet Marxist, confusing inputs with results. Another person taking marketing fluff seriously. ED glass may make reducing aberrations easier. Aspherical elements likewise. For general purpose LF taking lenses from Rodenstock and Schneider claims of apochromaticity are pure fluff. For process lenses, claims of apochromaticity are usually true.

[Nodda Duma]

Aspherical surfaces and ED glass are tools in the optical design toolbox, helping with certain aspects and having pros/cons but are not magical “solve-all” solutions.

Apochromatic refers to the number of wavelengths that are brought to the same focus. The side benefit of doing so is that the overall magnitude of color correction is generally significantly reduced compared to an achromat. The magnitude of the resulting color correction will vary from design to design. Again, it’s not magical and there are several strictly “non-apochromatic” designs which will have as good or better color correction. (Double gauss types and reflector-based imaging objective, for example).

[ic-racer]

... practical differences of Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses?
Nothing I can see in a B&W print.

[Bernice Loui]

Marketing Fluff, no single descriptor from this list can make your image better on it's own and much depends on how these optical design tools are applied to meet the goals of the optical designer.

What are the image goals of the artist-photographer? Based on that requirement, lens, film-process can be decided upon, then a camera chosen to support these goals.

The FAR more significant ingredient, Artist-Photographer.


Bernice



Hello folks,

Whats the practical differences of Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses?

Does Apo and ED serve the same purpose regarding chromatic aberration?

While aspherical lenses has better image sharpnes across?

Cheers
Peter

[Tin Can]

Wow!


Sigh. Another closet Marxist, confusing inputs with results. Another person taking marketing fluff seriously. ED glass may make reducing aberrations easier. Aspherical elements likewise. For general purpose LF taking lenses from Rodenstock and Schneider claims of apochromaticity are pure fluff. For process lenses, claims of apochromaticity are usually true.

[grat]

Ya'll need to be careful... One or two responses almost contained useful information not wrapped up in dogmatic hyperbole. :)

To the OP:

"apochromatic" is a term which is supposed to indicate the lens design is corrected for all three major wavelengths, leading to less color aberrations. It's also become a marketing term meaning "Very Expensive Lens".

"aspherical" is a lens design that is intended to increase sharpness across the field of view, as opposed to spherical designs which are sharpest at the center. Also frequently means "more expensive".

ED is referring to the actual glass used, I'll borrow B&H's description:


The chemical makeup of ED glass compresses the distance between each color’s plane of focus, resulting in greater color saturation, contrast and image detail. ED-type lenses also perform better in terms of light transmission, which makes for quicker focusing times and brighter images in your viewfinder.

How much each of these aspects contributes to the quality of your photo depends entirely on your subject, composition, lighting, film, etc.. It's typically more important in digital and especially digital astrophotography, where APO designs using ED glass will return much sharper results. With large-format, as you might have noticed from earlier responses, it's far less critical-- in fact, a number of LF photographers would prefer lots of fall-off, loss of sharpness, etc., and disregard any phrase with "color" in it. ;)

[Bob Salomon]

Ya'll need to be careful... One or two responses almost contained useful information not wrapped up in dogmatic hyperbole. :)

To the OP:

"apochromatic" is a term which is supposed to indicate the lens design is corrected for all three major wavelengths, leading to less color aberrations. It's also become a marketing term meaning "Very Expensive Lens".

"aspherical" is a lens design that is intended to increase sharpness across the field of view, as opposed to spherical designs which are sharpest at the center. Also frequently means "more expensive".

ED is referring to the actual glass used, I'll borrow B&H's description:



How much each of these aspects contributes to the quality of your photo depends entirely on your subject, composition, lighting, film, etc.. It's typically more important in digital and especially digital astrophotography, where APO designs using ED glass will return much sharper results. With large-format, as you might have noticed from earlier responses, it's far less critical-- in fact, a number of LF photographers would prefer lots of fall-off, loss of sharpness, etc., and disregard any phrase with "color" in it. ;)

For taking lenses it means that the lateral chromatic abberations in the secondary spectrum are corrected to a minute percentage of the focal length.
For other applications, like microscophy it means that the 3 principle colors are corrected to meet at a common point.

[Drew Wiley]

You don't see many examples of aspherical lenses in ordinary cameras because they are so darn expensive to make except in moulded plastic version. Up the road from me, it's a multi-billion dollar technology absolutely necessary for the highest order of astronomical and surveillance applications. No marketing hype involved.
And hope that the next medical micro-imaging you need truly knows how to align respective wavelengths. No hype there either.

[Nodda Duma]

It actually means correction at three wavelengths, so a bit more general than that. At least that’s what lens designers understand it as. I can’t speak for marketing misinterpretation.


Drew, polished (MRF) aspherics nowadays are about 2x the cost of equivalent spherical lens. Still a big deal for large astronomical refractors, but not so much for smaller (yet high-res) imaging objectives. They are ubiquitous outside the visible spectrum. It’s kind of nice now after worrying about cost of them for a couple decades...Even I’m more apt to use them for visible applications if I really have to push down size/weight. .

[pkr1979]

Thanks for the (useful) feedback fellas.

Maybe I should have mentioned I got curious about this when considering digitizing my eight-tens with a digital camera instead of a scanner.

[Drew Wiley]

Jason - I've pretty much got all the camera lenses I need, and obviously don't design them like you do. At this point in life I'd be happy with just a good used phase contrast trinocular microscope. Just for fun. It's been half a century since I took a degree in that nonsense, and, besides the print copy stand, the only application I have in mind for the digital Nikon.

[Ron (Netherlands)]

Nothing I can see in a B&W print.

Why do you think that achromats were developed and used in the early B&W era of photography?

[Ron (Netherlands)]

aspherical lenses are believed to provide a 'sharper' image in the corners also when the lens is used at full aperture, at least thats why I bought once the asph Summicron :-)
...and made of pressed glass...

[John Layton]

I once owned a 35mm asph Summilux - 2nd version with one (pressed) aspheric surface. Very stunning wide open by the way. The first version featured two aspheric surfaces...not pressed but ground. A very expensive unicorn these days!

My guess is that all of the LF aspherics were pressed (not ground). Is this assumption correct?

...but with all of this back and forth about "quality," especially when considered amongst the plethora of varialbles (atmospheric conditions, skill level, print size, etc. etc.), and while my non-aspheric lens lineup continues to provide me with great results, I am, especially as I currently print rather large (40x60) on occasion - still curious! At some point, I will give in and look for a 210mm Sironar-S...because I just need to see, and to know, for myself.

[Bernice Loui]

Owned and used Canon Aspheric "L" lenses for decades, they are excellent in every way. Some of the FD "L" series canon lenses became used in Canon's K35 cinema lenses first used by Stanley Kubrick and others. The real advantage of Aspherical optics for small formats is at full aperture. For LF, Aspherical optics IMO have lesser advantage. The only LF aspherical production lenses I'm aware of are the Schneider SSXL. Having owned and used the 110mm & 150mm since their introduction in the later 1990's they are GOOD, overall smaller than a similar lens with the same focal length.. The still have similar light fall-off issues and all that comes with a wide field lens.

Schneider had such a difficult time making uber precision moulded aspherical elements for the 110mm & 150mm SSXL, the initial batch had hand ground aspherical elements. Later production had uber precision moulded aspherical elements. This info came from the Schneider tech rep.. after waiting for nearly a year to get delivery.

These days, I'm back to using a 115mm f6.8 Grandagon as the 5x7 wide angle, and a 165mm f6.8 Angulon for the medium wide for 5x7. While both SSXLs are excellent, they did not make the print image THAT much better given the taking aperture typically is f16 to f32.

Really an example of what is a great advantage for smaller formats where large aperture are often used, when applied to LF, it becomes a lesser advantage.

As for "APO", APO process lenses have been the far preferred longer than normal focal length lens for decades. These APO process lenses are modest cost in barrel and work a LOT better than most would believe. IMO, the later version of APO plasmas are more of a marketing thing then clearly improved image performance.

Kodak has been using low dispersion Lanthanum optical glass since WW-II, then applied this glass technology to their Ektar lenses. IMO, the "ED" glass is another marketing moniker. What was a significant development was Canon's introduction of cultivated-grown Fluorite optical elements in the 1960's. While Fluorite crystals have been used for many decades in microscope objectives, Canon was the first to develop an crystal growing technology applying this to telephoto lenses. Today, Fluorite, ED and low dispersion optical glass is just another item in the optical glass catalog.. cost -vs- performance needs becomes the decider.

Honestly, majority of LF lenses are more than good enough for the majority of LF image making. Yes there are differences, it is knowing what the image goals are that should decide lens choice.


Bernice

[John Layton]

I will freely admit a tendency to gravitate towards utilizing an aperture of F/32, at least with my two “longer” focal length (210 and 305) lenses, as it often provides me with a good “sweet spot” in terms of giving me good results in the presence of a host of needs and variables. Having said this, I am quite certain that even at 210mm, such an aperture would represent something close to or slightly beyond diffraction limitation - which would make any discussion of “asph vs non-asph” moot, at least in a quantitative sense.

My fear in going to anything wider than F/32 (at 210mm and longer FL’s), aside from any needs for DOF…is that there may be (often is in fact), depending on ambient temperature and moisture levels (and “in situ” changes thereof), film-plane attitudes, film holder condition/manufacturing variables, etc., some amount of film plane migration from that which is “universally specified.” I actually know this to be the case after having done some pretty exhaustive testing of a variety of film holders, with a number of different film types, with a number of environmental variables (temperature/moisture/time/angle), and utilizing some very sophisticated measuring technology…while in the process of designing the L-45A camera. In short…its pretty amazing (and alarming!) how that film plane can jump around!

So maybe I have answered my own question? Still and all…I am curious!

[Drew Wiley]

Stopping down somewhat is critical to overcoming film holder variables, esp film sag. I use precision holders if the image might warrant significant enlargement like a 30x40 inch print. But that's still only nominal 4X from 8x10 film. Where ED and high Apo correction get important is when working with smaller MF cameras and color enlargements more like 7X or above. Nearly all post-60's lenses are well color corrected, but that was not always the case.

[pkr1979]

This is more interesting then I thought it would be. As far as I understand, though, is that a APO-corrected lens is useful for reproduction and scanning (with dslr) large format negatives with, while its not that important its aspherical as you can stop down anyway?

[John Layton]

This discussion is starting to make me wish that glass plates would make a comeback. Hmmm...maybe I need to connect with Jason? Panchro at ISO-2 could be limiting...or liberating? Ortho at ISO 25...hmmm - could work wonders for deep woods work, not so likely for open ocean images.

Seriously...to have something so dimensionally stable (as glass plates) - I'd be stepping up to whatever challenges I'd need to overcome to realize this!

[Bernice Loui]

This discussion has come up before..

To even begin to achieve good performance from the lens, film flatness is a MUST. This is one of the fundamental reasons why going up in film format size makes achieving film flatness difficult. To deal with this problem adhesive and vacuum film holders can be used to help film flatness with increasing film size. Film flatness is one of the fundamental reasons why 8x10 can be a problem to realizing all a give lens can produce.

Camera alignment is another significant factor, folder cameras might not have any where near the precision and repeatability of alignment of standards needed to achieve what the lens can render. Problem is increased with larger lens apertures used. This is why stopping down is often the solution to remedy both these problems.. except lens performance will be reduced as the image taking aperture shrinks... resulting in "sort-of-focus". Not much of a problem if contact prints are made from 8x10 or larger film, problem if the film is projection enlarger to any significant degree.

Glass plates are flat, flatter than film in a film holder.. problem with camera precise and alignment remains regardless of how flat the image recoding device or media is.

This is why process cameras back in the day had vacuum backs on a precision flat film back. Camera alignment was check, adjusted, calibrated. Using a vacuum film back large sheets of film (could be feet x feet in size) could be held remarkably flat as needed for precision graphics work.

Simply going down film format size can make a surprising difference in easing film flatness problems.

Lens performance is one factor out of many that will have an effect on the finished print.



Bernice



This discussion is starting to make me wish that glass plates would make a comeback. Hmmm...maybe I need to connect with Jason? Panchro at ISO-2 could be limiting...or liberating? Ortho at ISO 25...hmmm - could work wonders for deep woods work, not so likely for open ocean images.

Seriously...to have something so dimensionally stable (as glass plates) - I'd be stepping up to whatever challenges I'd need to overcome to realize this!

[Bernice Loui]

How much image information is contained in the original sheet of film -vs- what can be recored by any image digitalizing device?

Once the film image is digitized, information will not be identical to what was on film. Will digitization of the image be good enough, that depends on what the image goals are.


Bernice


This is more interesting then I thought it would be. As far as I understand, though, is that a APO-corrected lens is useful for reproduction and scanning (with dslr) large format negatives with, while its not that important its aspherical as you can stop down anyway?

[Drew Wiley]

There are all kinds of different paths to optical design. But in our mortal realm, cost efficiency is always a factor in manufacture. We aren't the real large format photographers with real money because we use tripods and not observatories. And there has to be enough market demand for certain specific glass types. The realistic options have changed over time. Most of today's lenses involve computer design and are likely to exceed what "cult lenses" of former years could do in terms of specs. Image rendering personality is a somewhat different lens topic; and I'm personally unqualified to comment on the best kind of beer bottle glass for doing that.
pkr - most brand-name 35mm macro lenses are going to be very well corrected. I wouldn't worry about it too much. You don't have to pay thousands of dollars. But anything that tiny is going to involve a compromise. Going from sheet film originals to small digi camera scans is sorta like trying to feed a pet hippo through a keyhole. Yes, I'm set up that way to make basic web-usable copies of prints; but that's a very low threshold and small scale of reproduction. All the prints themselves were printed optically right from sheet film originals.

[pkr1979]

Bernice, the goal would be to get a digitized copy that contains as much as possible of the original information. Today I use a drumscanner I got at a reasonable price - and it works quite well.

Drew, I’ll get that hippo through eventually ;-) I dont know to much about these pixel shift cameras, but I imagine this function should be very useful for 'scanning'... Im not getting a Fuji GFX 100 today (able to do pixelshift with the new firmware), but this technology is probably available at a more sensible price in ten years. A 'decent' lens is probably useful in such a setup. What I here you say though, is that Fujis 120 macro is probably going to be sufficient - not expecting you to be familiar with that particular lens that is :-)

I have a Rodenstock APO 360mm repro Ive been using with my 8x10 and its the sharpest lens I have... I never really use it though... its just too clinical. Im sure its very, very useful for its intended use though.

[Bernice Loui]

Theoretically, a GOOD drum scanner in proper operating condition and properly used should yield good scans from film to digital files.

Never found any APO process lens (APO ronar, APO artar, APO nikkor and..) to be "clinical" they have excellent optical performance and color rendition and has been the far preferred table top lens from back in the color transparency days. They also make excellent longer than normal focal length lenses.


Bernice

[Drew Wiley]

Bernice, what I would personally refer to as "clinical" in my own set of Apo Nikkor dialytes is that the out-of-focus blur or "bokeh" is rather busy and not nice and soft like my older Zeiss tessar f/9 process lens of comparable focal length is, although it too is very sharp and fully apo corrected. Some people might not find modern barrel process lenses ideal for things like portraiture or other selective focus applications.

[Bernice Loui]

Yes Drew, for images that need most of not all of the image in focus by stopping down to f16 and smaller, not a lot wrong with an APO process lens as out of focus rendition becomes a LOT less important. When out of focus rendition at larger taking apertures, it's back to something like a Kodak Commercial or similar Ektar or Schneider Xenar.. All depends on what the image goal is.


Bernice