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I have some notions of geometry and I am currently trying get a full grasp of some features of perspective. I am having a hard time understanding the relation between the observer and picture plane since I am having troubles making the distance between them reflect in the drawing. I have done these drawings of the same model just moving the observer closer to the picture plane. I am using the picture plane to define the real measures. When I look at both at same time I know that something is off but can't really tell what. Can someone here explain what I am doing wrong and help me understand this relation? Thanks a lot!

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No drawing errors! When the observer is further from the picture plane, the relative distance differences are lower and the apparent size differences between the parts of the target are smaller. You should take one of your drawings and try to see how the sight lines would move if you moved the observer further.

This subject is discussed here before. One example:

How does the distance between stationary point and picture plane effect perspective?

Your original goal - to reflect existing distances between the parts of the target in a perspective so that the distances could be found from the image is impossible. You cannot know which apparent length difference is caused by perspective and which is caused by the different sizes or distance differences of the parts. The nature has given to us 2 eyes to solve the ambiquity - not exactly, but well enough to stay alive.

  • Well, thank you for your answer. I spent a considerable amount of time trying to reason it out but I always got to the same conclusion. My doubt was if I was wrong to put the real size always in the picture plane regardless of the distance but if not I wouldn't know where to put it. The results are somewhat counterintuitive but I guess it makes sense. Thanks again – António Quadrado Jan 27 at 17:06
  • @AntónioQuadrado It may be better f you think the picture plane as being behind the lense (its the same thing we dont jsut like dealing with upside down images), in case of the human eye this plane is actually a spherical surface. – joojaa Jan 27 at 20:44
  • You mean the lense of the eye, @joojaa? – António Quadrado Jan 27 at 21:59
  • @AntónioQuadrado or a camera, or a pinhole. But not a compound eye. – joojaa Jan 27 at 22:02

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