File talk:Gregorian telescope.svg

I think the lower 2 incident rays (green and purple) may be the wrong way round (they need to be swapped). When reflected, the present diagram has the incident green ray with a smaller angle of incidence than the purple ray, yet it has a larger angle of reflection than the purple ray (inconsistent with the law of reflection). Also, the incident green rays as presently drawn represent diverging light from a closer location than the incident purple rays. This would show "depth", but the final image indicates that the purple and green rays show the image at the same distance. Therefore, it is most likely that the lower 2 incident rays simply need to be swapped before their first reflection.