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Forums Cinematography green screen field of view & distance calcuator?

  • green screen field of view & distance calcuator?

     Mark Suszko updated 1 year, 2 months ago 3 Members · 7 Posts
  • David Patterson

    August 14, 2020 at 3:39 pm

    I’d love to find an app that allows me to determine how large a green screen I will need for shooting talent, while calculating the lens field of view and factoring in the distance of the talent to the green screen. I have seen a few apps that calculate field of view (I use Cadrage), but I have to be on set to see the FOV.

    Ideally, I want to previsualize how much studio space and size of green screen I would need to (1) properly distance talent from the green screen to avoid color spill, (2) avoid talent being near the edge of the green screen, and (3) estimate space for lights and camera position. This would be helpful in evaluating locations, and explaining to clients green screen size why some spaces aren’t adequate.

    BTW, I have shot plenty of green screen footage, so I know the process and pitfalls. I’m not looking for info on technique, but rather info on how to calculate the space and size of green screen I will need.

    I imagine someone with good math and programming skills (not me!!!) could build a calculator with a graphic interface to demonstrate this. Maybe an app already exists?

  • Todd Terry

    August 14, 2020 at 3:52 pm

    I don’t recall ever having need for that, but it’s not a bad idea.

    I’ll note there is one more variable that is needed to plug in… you also need to know the distance from the camera to the talent, in addition to the ones you mentioned (field of view or focal length and distance from talent to greenscreen).

    Hmmm… wait, no… I’m wrong about that. Actually, now that I think about it, you don’t absolutely have to know either the distance from the camera to talent, or the talent to greenscreen. The only factors you need to know are focal length (or FOV) and distance from the camera to the greenscreen… it makes no difference how close the talent is to it to know how big a greenscreen you need to fill the frame.

    I can’t say I’ve ever seen such an app (though not saying it doesn’t exist). With all the various calculators out there it shouldn’t be that hard for some savvy app person to develop it… if they had a market for it (couldn’t say whether that exists).

    In the meantime, I think that’s just gonna take a bit of drawing and math. Break out the protractor and calculator.

    I’ve never needed that or had to ask “How big a greenscreen do I need” because I already have what I have. We have two greenscreens that occasionally go on location. The small one is about 5’x8′ and the bigger one is 10’x20′. So we’ve just always gone with what we had on hand, rather than trying to determine an exact size we might need.

    It would be helpful though especially in, say, a permanent or semi-permanent setup… for example, if you were painting or building a greenscreen wall or cyc and didn’t want to create more than was necessary or areas that would never be used.

    T2

    __________________________________
    Todd Terry
    Creative Director
    Fantastic Plastic Entertainment, Inc.
    fantasticplastic.com

  • David Patterson

    August 14, 2020 at 4:39 pm

    I have a 12 x 20′ green screen, but in my experience I do need to know distance relationship of camera, talent and green screen. The closer the talent is to camera, the larger a green screen is required (to avoid the talent exceeding the area of the green screen). The closer the talent is to the green screen, the greater the risk of color spill. Cadrage app gives me a great idea of my camera sense/lens combination for FOV, but I need a way to do this when away from set to see the relative space and distance between talent and green screen.

    The other factor is having ample room to light the green screen and talent separately. All too often a client will assume I can cram a green screen into a space that doesn’t allow for lights and/or the ability to get talent far enough away from the green screen. The last thing I want to do is hand off footage that will be hard to key to an editor.

  • Todd Terry

    August 14, 2020 at 4:49 pm

    Yes all of that is true… I’m just saying from a technical and calculatable math standpoint, it makes no difference where the talent is, the only factors that are important to the math are the FOV and distance from the camera to the screen.

    If you know where you want your camera, and you know where the screen will be, and you know where within the FOV where you want your talent to frame them like you want for the action you want and be able to light the screen and the talent where you like, those are all fine and good aesthetic choices, but they don’t have any bearing on the math determining how big the greenscreen should be to fill the frame at a given distance.

    Unless I’m missing something.

    It’s actually a very simple calculation, but I still don’t know that any such app exists.

    T2

    __________________________________
    Todd Terry
    Creative Director
    Fantastic Plastic Entertainment, Inc.
    fantasticplastic.com

  • David Patterson

    August 14, 2020 at 5:05 pm

    Terry – Thanks for your comments. I probably wasn’t clear in my intent, but I am simply looking for a way to calculate the size of the green screen and space requirements for a shoot. Having shot in many green screen situations, I know all to well the need for adequate space to properly frame talent and light a green screen.

    Even if I have a huge space where I can place talent, lights and camera where ever I want, I still need to insure that the size of the green screen will exceed the area of the talent. Things get complicated when I’m given a small space to work with, and my choices for camera, lights, talent and green screen space are restricted.

    At the moment, I have a client who thinks we can shoot 2 people, head to toe, in a small room. There is not enough space to fully open my 12×20′ green screen, position the camera, lights and talent to achieve this, so I was hoping to find an app that would demonstrate this to them. For now, I’ll just draw out a FOV and lighting diagram while they grovel over the cost of hiring a proper space.

  • David Patterson

    August 14, 2020 at 10:32 pm

    I found this app that essentially does everything I need except indicate the dimensions of the background. It’s actually a great visual simulation for FOV and DOF, but there is not way to indicate what would be the size of the green screen. So close, and yet so far…

    https://dofsimulator.net/en/

  • Mark Suszko

    August 17, 2020 at 7:47 pm

    Just curious if you couldn’t model this situation in Sketch-Up? It will work with real-world dimensions, and doesn’t require artistic skills. If the point is to show the client the situation, that kind of visual example is going to do it for you faster and easier than showing them calculations. You could even place real world photos in the sketch up space to help them visualize.

    A more expensive version of Sketch-up than the free version, is made to be used for story-boarding and pre-viz, and will simulate the actual frame appearance based on lens setting you input, and could show your FOV for green screens that way.

    And I know you know this, but unless the actor is moving around a lot, – walking or jumping or whatever – you only need about an inch more screen than they can reach out with their hands because everything else gets garbage matted or roto’ed anyway.

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