Why does moving the station point change the COV but not if you move the picture plane?

To my limited knowledge I understand that moving the station point further away from the picture plane results in having a bigger cone of vision. If I have a flashlight and move a couple of steps back from the picture plane the circle of light from the flashlight will expand, just like the cone of vision.

However I have read that moving just the picture plane wont affect the cone of vision and I cant understand why?

Edit: I am curious about the size/scale of the cone of vision, not necessarily the angle

• Picture plane is a purely virtual construct so that you can do measurements. It does not really matter where it is. Oct 15, 2018 at 21:06

Cone of vision is measured as horizontal and vertical angles. Only those objects are in the image which are inside the cone.

In the left yellow and cyan blocks are out of the image.

In the right the station point has been moved further. The cone of the vision is as many degrees wide than in the left, but now also yellow and cyan blocks are in the image. COV can now be considered to be bigger because it catches a bigger part of the existing objects to the image. This is, what you already had noticed. But remember: In degrees the COV is still the same.

Go back to the left drawing. Think what happens, if the imaging plane is moved further (=new imaging plane). If the cone of the vision is the same, no more objects will step into the image. Yellow and cyan blocks will stay out. The image is only scaled to a bigger size, but it doesn't contain bigger part of the existing objects.