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  1. #1
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    Handprint's cov/view distance question

    Hi, I'm a little confused about some things in the first two chapters of handprint's tutorial.

    On page 14/31 of Perspective of the world (http://www.handprint.com/HP/WCL/perspect1.html#setup Under Circle of View Framework, the last subsection of Perspective Setup),
    the author states that the 90° circle of view is a convinent framework to use as the Viewing height, Radius of circle of view and Viewing distance are all similar. Assuming the viewing height is that of an average human, the viewing distance would be 1.7m away from the image plane.

    1. Is it right to assume this refers to a position where the vp of the objects in the image coincide with the rough vp of the human eye?

    On page 31/45 of Central perspective (http://www.handprint.com/HP/WCL/pers...isplaygeometry last few paragraphs of 'Viewer dimensions of the display geometry'),
    the author says that 2.5x Controlling dimension (the longer side of the framed dimension) is the optimal viewing distance. But if the image frame is large, say, 2m. That would make the viewing distance 4.5m.

    2. Does this mean that the author used a 90° circle of view but scaled the image frame : view distance ratio at 2.5x which would crop the circle of view at to a comfortable range (in his case, 30°)?
    In another situation, a scale to view distance ratio of 1 : 1 would preserve the 90° circle of view. This would make the VP of the objects in the image the same as 90cov which is the sortof like the human eye?

    3. Is it right to say that a [long camera (300mm) focal lens = nearer VP = moving closer to the image/picture plane] while [short focal lens (10mm) = further apart VP = moving further from the picture plane]?

    4. Or is making a extreme/long shot only dependant on how much wider you make the circle of view (that was 90°) to the image plane is? So making a CoV radius that's larger will give a wider fov and spread the VP further apart.

    5. Not sure what the mathy sections about trigonometry are but isn't it the same as using an object of a size you determine and receding to other VPs as a relative size indicator along with a measuring point for depth?

    Thanks a bunch!
    Last edited by eezacque; 4 Weeks Ago at 11:14 AM. Reason: Fixed tags


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  3. #2
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    This author is extremely abstruse (and hence not very helpful) but here's my take.

    1. He means that for whatever reason it is convenient to define the eye to be a distance 1.7 m (average human height, apparently) from the ground and from the picture plane (they don't have to be, for example a person could stand 5 m from the picture plane, or be on a hill overseeing the picture plane, say, from 20 m above). And then all three (distance from the center of vision (principal point) to the edge of the 90 degree circle of vision, distance from the eye to the picture plane (viewing distance), and distance from the ground plane to the eye perpendicularly (viewing height)) are all equal.


    So placing the figure at a distance equal to his height (~1.7 m) from the picture plane in the picture below. This will yield the distance from the intersection point of the central ray here to the intersection point of either of the two other rays to be equal to 1.7 m. Why that's useful I don't know.

    Name:  image.png
Views: 341
Size:  408.0 KB

    "position where the vp of the objects in the image coincide with the rough vp of the human eye"
    There is no VP of the human eye, there is just eye. We intersect rays from points on objects behind the picture plane with the picture plane such that the rays go through the eye. This is always true. That's what we mean by perspective drawing.

    2. Yes, if I understood correctly.

    3. Don't understand camera stuff too well, but I think shorter lens corresponds to smaller circle of vision and hence farther away vanishing points, because focusing on a smaller part of the visual field means the same vanishing points are now farther relative to the new frame.

    http://vintagelenses.com/wp-content/...zeissrange.jpg

    Handprint's cov/view distance question
    Last edited by onemax; 4 Weeks Ago at 05:16 PM.


  4. #3
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    As for 3., a shorter lens will place vanishing points closer to each other, emphasising the perspective, while a longer lens will flatten the image.
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  6. #4
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    Quote Originally Posted by onemax View Post
    3. Don't understand camera stuff too well, but I think shorter lens corresponds to smaller circle of vision and hence farther away vanishing points
    the opposite...

    Quote Originally Posted by onemax View Post
    focusing on a smaller part of the visual field means the same vanishing points are now farther relative to the new frame.
    is true. (you contradicted the first part in the second, so first=untrue, second=true)

    the shorter your lense the bigger your circle of vision, the closer the vps = more distortion.
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  8. #5
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    Oh, right, I meant longer not shorter. Ugh.


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