Diffractive Optics

Discussion in 'Beyond the Basics' started by Buszaj, Apr 11, 2008.

  1. Buszaj

    Buszaj TPF Noob!

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    Hey everone, just wondering about diffractive optics. What does it do, why is it so expensive?

    Thanks
     
  2. Garbz

    Garbz No longer a newbie, moving up!

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    It's a lens with an optical diffraction grating in the middle. The purpose is that it corrects the fact that light bends at different angles depending on their wavelength.

    This is called chromatic aberration (red / cyan) fringing on the edge of sharp contrasts when shooting wide open. And the Diffractive optics uses the principle of diffraction to correct it.

    Have a look at Canon's marketing material by doing a google search and it'll show you an example drawing of what this lens looks like. It should be pretty clear that this is an insanely hard design to cut and polish.
     
  3. Alpha

    Alpha Troll Extraordinaire

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    No offense Garbz, but screw Canon. Really. Screw Canon. They were one of the last manufacturers to develop an APO lens. Why give them so much credit for the technical aspects of building one?
     
  4. JerryPH

    JerryPH No longer a newbie, moving up!

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    Holy crap dude, no one gave cedit anywhere. You asked a question, Garbz gave an aswer. If you do not like the answer, at least have the courtesy to thank the person helping you and keep your severely negative opinions to yourself.
     
  5. Alpha

    Alpha Troll Extraordinaire

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    Jerry, clean your glasses. I didn't ask the question. Someone else did.
     
  6. Buszaj

    Buszaj TPF Noob!

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    Whoa, take it easy. Garbz did not say that Canon invented the idea, but that they have detailed drawings of all their lenses.
     
  7. Alpha

    Alpha Troll Extraordinaire

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    Just stressing the fact that this is hardly a proprietary design.
     
  8. Garbz

    Garbz No longer a newbie, moving up!

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    Jesus go get a massage and cup of tea or something and calm down. He asked about diffraction optics, not APO. Since he asked for the canon marketing term I told him to go to the canon marketing website where they can blow their own horn, just like if he'd has asked for VR I'd have sent him to Nikon's website, or IS I'd send him to Canon, or HSM I'd send him to Sigma.

    I assumed he's a canon user since he asked for "Diffractive Optics"

    I never said they invented it. Hell I'm a Nikon shooter, Canon users have big enough heads as it is :p
     
  9. JerryPH

    JerryPH No longer a newbie, moving up!

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    Go take a valium. You were the one off the hook... and I do not wear glasses. ;)
     
  10. Jon, The Elder

    Jon, The Elder TPF Noob!

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    Well....that was certainly a pleasant little interlude.
     
  11. usayit

    usayit No longer a newbie, moving up!

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    Yes it was...

    Alpha should be especially embarrassed....

    First... he read misinformation into Garbz post
    Second... APO = apochromatic optics
    READ>> http://en.wikipedia.org/wiki/Apochromat
    Third... DO = Diffractive Optics
    READ>> http://www.usa.canon.com/consumer/controller?act=CanonAdvantageTopicDtlAct&id=2632

    Two completely different technologies in optics...... APOs don't have diffractive grating in their glass elements.....


    My limited understanding leads me to believe that APOs and DOs both control chromatic aberration but do so in different ways. The "Canon Advantage" to using DO optics is that it can achieve good control over CA with less glass... which results in a compact and lighter package. The compact and lighter package is the big selling point..... although I myself don't really care for DO too much. I believe Canon (and many lens manufacturers) were employing APO type elements well before DO was even on the drawing board.


    btw.. Do other manufacturers of lenses have an equivalent technology to Canon's DO?
     
  12. Garbz

    Garbz No longer a newbie, moving up!

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    Actually apochromatic optics is just the generic term used for correcting CA.

    Sigma uses the "APO" technology and show the marketing department has no creativity what so ever, Nikon use ED coatings, and I believe Nanocrystal coatings also have an APO effect, Canon has DO and another I believe, but the principles are similar, bring light beams projected in different places through the colour spectrum to the same point.

    The jury is out on whether this is best achieved by using a diffraction grating, or by using a coating that varies the refractive index, or what not. They each have their plusses and minuses. The obvious minus on the DO is the cost of producing the element is high.
     

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