Relation between picture plane and observer in perspective

Question

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!

Answer 1

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.