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Thread: Diffraction. When does it really matter with LF?

  1. #81
    Mark Sawyer's Avatar
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    Re: Diffraction. When does it really matter with LF?

    Quote Originally Posted by Nodda Duma View Post
    Because it is not a geometric effect.
    That makes sense! Thanks!

    But is chromatic aberration a geometric effect?
    "I love my Verito lens, but I always have to sharpen everything in Photoshop..."

  2. #82
    Nodda Duma's Avatar
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    Re: Diffraction. When does it really matter with LF?

    Quote Originally Posted by Mark Sawyer View Post
    That makes sense! Thanks!

    But is chromatic aberration a geometric effect?
    Yes, they are wavelength-dependent geometric effects.

    Sphero-chromatism: focus vs wavelength
    Lateral color: Distortion vs wavelength

    Fun fact: Focus is considered an aberration... the only 1st order aberration. Corrected by adjusting focus
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  3. #83
    Drew Wiley
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    Re: Diffraction. When does it really matter with LF?

    Hi Jason - I was hoping you'd chime in with your expertise. But what I saw in each instance was in remarkably clear calm air. Yes, there could have been a rising heat differential somehow, but this was far too crisply defined to be termed heat-wave related. About all I'm qualified to state is that it was some kind of prismatic phenomena, light waves actually being differentially bent or refracted over sharp high edges. I have numerous color photograph of that at high altitude, using highly corrected lenses, and it's significantly more apparent than what you noted. Crisp lines directly over and perfectly copying the details of sharp ridgelines - one line violet, the other distinctly warm hued. Last saw it with my naked eye about 3 years ago in the evening after an exceptional storm at high altitude created the clearest air and deepest blue sky that I've seen in the high Sierra for many decades. The sun was setting the the opposite direction, so it can't be attributed to that. Same case every other time I've seen it - the sun was setting the opposite direction, except atop Kauai, where it was at-mid day. But light can do unusual things in the Islands, bouncing off marine cloud layers below.

  4. #84

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    Re: Diffraction. When does it really matter with LF?

    Now what about when a little wind is thrown into the mix...

  5. #85
    Drew Wiley
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    Re: Diffraction. When does it really matter with LF?

    Then no more crisp lines. This last time I saw this was in fact when the air was unusually calm and clear ... an ominous sign in the high country because it means a big bulldozer of a storm front is right behind it, which was already in full force right over the next divide. I was high enough to get some good shots of that. But I did have one more day to get below timberline, and then when I was snowed in for a few days, I was in the mood for a good long rest in the tent anyway. Had already walked 75 miles on blisters and had another 25 to go. And it was a lovely campsite right next to the river and lots of wonderful unhurried photo opportunities. Drymounted another print from that trip yesterday. One of the colder blizzards I've experienced in September, however.

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