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

  1. #1

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

    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

  2. #2

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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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.

  3. #3
    Nodda Duma's Avatar
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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).
    Newly made large format dry plates available! Look:
    https://www.pictoriographica.com

  4. #4
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

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

  5. #5

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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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


    Quote Originally Posted by pkr1979 View Post
    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

  6. #6
    Tin Can's Avatar
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    Wow!

    Quote Originally Posted by Dan Fromm View Post
    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.

  7. #7

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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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 colorís 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.

  8. #8

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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    Quote Originally Posted by grat View Post
    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.

  9. #9
    Drew Wiley
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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.

  10. #10
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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. .
    Newly made large format dry plates available! Look:
    https://www.pictoriographica.com

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