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

  1. #11

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

    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.

  2. #12
    Drew Wiley
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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.

  3. #13
    Ron (Netherlands)'s Avatar
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    Quote Originally Posted by ic-racer View Post
    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?
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  4. #14
    Ron (Netherlands)'s Avatar
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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...
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  5. #15

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

    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.

  6. #16

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

    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

  7. #17

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

    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!

  8. #18
    Drew Wiley
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    Re: Aspherical, Apo(chromatic) & ED (extra low dispersion) lenses - whats the differe

    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.

  9. #19

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

    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?

  10. #20

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

    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!

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