>>12258718The distance between vanishing points depends on the angle you are looking at them.
Draw a line from the focal point to each VP and also draw a line from the FP that is normal to the projector screen.
The distance between two VPs is
L*|tan(t1)-tan(t2)|
where L is the focal length and t1,t2 are the angles between each VP and the normal.
The angle of your field of view, T, is determined by your focal length, L, and the width of your projector screen, W.
(W/2)/L = tan(T/2)
The field of view can be increased by making the projector screen wider or decreasing the focal length.
