Originally Posted by

**Dark Photon**
Right. Eyepoint is a perspective concept. With orthogonal, you still transform to eye-space as usual (an orthonormal space), but then instead of applying a projection which converges to a point in space (the eyepoint), your projection is a 3D box (more correctly, a rectangular parallelepiped). You clip to that box and smash it directly onto the screen. Your eye/camera is effectively a plane rather than a point in space.

This is the same as the difference between a point light source and a directional light source. You're just tracing rays in the opposite direction.