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    Quote Originally Posted by tom roper View Post
    tl;dr.


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    Quote Originally Posted by DLD View Post
    tl;dr.
    yd;ln

    Spoiler alert


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    Quote Originally Posted by Tom Roper View Post
    Ah, a wild Yedlin sighting - also known as the Abominable Resolutiondude.

    "♫ Do you wanna build an image? You don't need many K's ♫"


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    Here is an actual tl;dr for what I was saying:


    fig-1-fls.gif


    fig-2-fls.gif



    These are from this lovely article here: https://www.edmundoptics.com/knowled...g-information/


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    Senior Member James0b57's Avatar
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    Quote Originally Posted by Joshua Cadmium View Post
    Here is an actual tl;dr for what I was saying:




    These are from this lovely article here: https://www.edmundoptics.com/knowled...g-information/
    Yes, I think that is a big part of what you were saying earlier. You weren't talking about diffraction in the visible to the naked eye sort of way that old times photographers talk about it, but you were talk about diffraction between microscopic photo sites that are at the sub pixel level, since it may only effect one or two colours at a time. Even with lens projectors blowing up a chart pattern into a 2meter area, that kind of diffraction will still read as "sharp" to the eye, but perhaps be just enough diffraction to reduce moiré.

    Also, all of the moiré cases I have seen are in the center of the frame. As chances are that at F1.4, or f2, the lens will not perform well enough to allow moiré in the corners or edges of the lens. those that shoot 2.40 or 17.9 and use rule of thirds and maybe even push the edges of composition towards the left or right may never see moiré at F2.8.


    Reason I found the your comments fascinating, is that I never realized that a good lens at F2, in the center might resolve sharper than F5.6 in the center, if that is what you are getting at.

    JB has been pretty public about liking lenses with a more vintage feel, and they may have just enough diffraction inherently as to not cause him grief with moiré, whereas a Canon Cine Prime at ~f2 in the center might just do it.


    I'd rather read your comments here and feel some sense of "ooooooooh, gotcha.' than scratching my head and going, "....I sweaR, THAT NEEEEVER happens."
    Last edited by James0b57; 10-23-2020 at 11:45 PM.


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    Quote Originally Posted by James0b57 View Post
    Yes, I think that is a big part of what you were saying earlier. You weren't talking about diffraction in the visible to the naked eye sort of way that old times photographers talk about it, but you were talk about diffraction between microscopic photo sites that are at the sub pixel level, since it may only effect one or two colours at a time. Even with lens projectors, blowing up a chart pattern into a 2meter area, that kind of diffraction will still read as "sharp" to the eye, but perhaps be just enough diffraction to reduce moiré.
    You nailed it! Yes, my whole point in studying this was to determine where there could be a difference in moire and if a mild diffraction could explain that difference. I knew JB was using sharp, modern, well corrected lenses (Zeiss Supreme Primes) that might be sharper than what the Youtube testers were using, so where was the difference? I figured that the testers might be using the lens more wide open, which you might be able to get away with in interviews, but JB was using deeper DOF, since f4-5.6 seems to be more common in narrative work. I was wondering if diffraction might play a role and then looked at the math about where diffraction was, and I was like, ooohhhh, that makes a whole ton of sense.

    Also, the photosite level is the pixel level when it comes to diffraction, since they are the same size (I am using the term photosite instead of sensor pixel, since it is more technically correct. Instead of photosite you could also say undemosaiced pixel.) Even though the final pixel may be made from a composite of multiple photosites blended together, all of those photosites will experience the same ratio of diffraction.

    And while the photosite on the 12K is small at 2.2um - it's not microscopic when you punch in - you're going to see blurriness at a per pixel level if you are in serious diffraction. For instance, you could very realistically throw away 3/4 of the resolution of the 12K sensor by stopping down to a small f stop - like f16 (or around there - I'm just guessing f16, which is similar to shooting f32 on the A7RII.) That's still 6K worth of resolution - even on a 4K monitor that's still going to look good with maybe some light sharpening added. If you punched into an HD crop, though, that's going to be a different story. You might be shocked to see blurry, DVD quality resolution.

    Even the images I just listed don't tell the whole story - it's another simplification. Line pairs (like the black pixels in between the colors in the images) are used to determine resolution because it is very easy to see and measure - a loss of resolution is the same as a loss of contrast because the black and white lines are blurring together to make gray. However, black is the absence of light, which is not always a good representation of the real world. Because of that, it might be better to imagine that you have colors of light right next to one another that are blurring each other into wrong colors. For instance, if you put red and blue lines right next to one another and added diffraction, BOTH pixels would start to turn purple from opposite ends of the spectrum. Or you could have one skintone color right next to another skintone color, with diffraction causing both to blur into a single block of the same color or close to it. You are going to lose both fine detail and color information from diffraction.


    Quote Originally Posted by James0b57 View Post
    Reason I found the your comments fascinating, is that I never realized that a good lens at F2, a lens might resolve sharper than F5.6, if that is what you are getting at.
    Yes, I had no idea this was a thing - that points of light get bigger as you stop down. It seems so counter-intuitive, but it makes so much sense about why diffraction happens. So, yes, on small pixels, f2 may be sharper than f5.6. But, again, what really matters? f5.6 may serve the image or the story better than the more resolutionally maximizing options.
    Last edited by Joshua Cadmium; 10-24-2020 at 10:51 AM.


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    Zeiss supremes (not the same as Arri Signature, which have nothing to do with Zeiss) are nice, but they aren’t perfect. They have some visible chromatic aberation, even more so than sigma or canon possibly.
    Last edited by James0b57; 10-25-2020 at 11:38 AM.


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    Quote Originally Posted by James0b57 View Post
    Zeiss supremes (not the same as Arri Signature, which have nothing to do with Zeiss) are nice, but they aren’t perfect. They have some visible chromatic aberation, even more so than sigma or canon likely.
    Oops! Yes, I know the difference, I just misspoke.


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    @ Josh and John Brawley I understand the connection between the limits in size of the Airy disk and photosite size, an am aware of the 2.5 constant for calculations. But why does the physics decide on a 2.5 constant? What does it mean, where does it come from?

    Quote Originally Posted by Joshua Cadmium View Post
    One more thing I wanted to mention about using 2.5x pixel width for diffraction. The calculators online and what I have been using is based on light being at green (usually 550nm) since that is right in the middle of the spectrum. But just using green doesn't tell the whole picture.

    Violet light (just at the edge of UV) is around 400nm, which means it actually creates a smaller Airy Disk at every f stop. So, using that 2.5x number on the 12K (a width of 5.5um) but with 400nm light, we get violet light diffraction right at f5.6. That's a much deeper f stop than the f4.1 you get when running the math at 550nm. [The math, once again, is 5.5um = 2.44 * 400nm * f stop. OR f stop = 5.5um / 2.44 / .4um]

    Far red light is around 700nm, which means it creates a larger Airy Disk at every f stop. The 2.5x math puts far red light diffraction at f3.2.

    Warmer tones are going to experience diffraction before cooler tones do. That's just the physics of light.


    For comparison at 2.5x width:

    400nm = f5.64
    550nm = f4.10
    700nm = f3.22

    For comparison at 1.5x width:

    400nm = f3.38
    550nm = f2.46
    700nm = f1.93

    For comparison at 1x width:

    400nm = f2.25
    550nm = f1.64
    700nm = f1.29


    Is this helpful? Maybe not to everyone, but I certainly find it absolutely fascinating. It also again shows why that 2.5x defacto standard for diffraction is just a simplistic number like any other rule.


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    Quote Originally Posted by Joshua Cadmium View Post
    Oops! Yes, I know the difference, I just misspoke.
    I also probably exaggerated the flaws in the Supremes anyway. They are plenty sharp, and gorgeous. At a first glance they seem sterile and all the negative "Zeiss-y" connotations, but they really are wonderfully done. They are a bit on the contrasty side, but even within the shadows, they still have a lot of subtle detail. The CP.2 and CP.3 are similar, but more inky black in the shadows. The colours seems to read more true on the Supremes than the CP's. Somehow the even-ness and balance in image characteristics that the Supremes have really work well, and I might even dare say they verge on unique in this sea of lenses, while maintaining all the positive "Zeiss-y" attributes, as well. Paradoxes can be nice. Or nice things are often paradoxes? Is that true? I suppose it is if you look at anything too closely.

    .....ah well, not a busy Sunday.


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