Extended rays for only one element

[LSV-JR]

I am trying to simulate a system of lenses to see how changes to one element affect the image. I think Extended Rays is what I want, but turning it on creates an unreadable mess because it extends every ray, when I only really care about extensions from the final element surface.

In my specific case I have a hollow sphere with a few additional elements inside, created from multiple overlapping elements with Refractive Index adjusted per the tooltip (exterior medium, cutout for sphere (to make my IOR calculations easier), circle for outer sphere surface, circle for inner surface, additional elements as needed)

[ricktu288]

In your case I guess you can use View -> Seen by observer. Note that you can make the observer quite large by adjusting Settings -> Observer size. If the blue color of the extensions are not clear enough, you can adjust Settings -> More scene settings -> Theme -> Default observed ray.

As for the proposal for only showing extended rays for specific elements, I am not entirely sure whether it can solve all the problems of this type, as sometimes the mess is not because extensions from many elements are shown, but because the rays are interacting with the same element multiple times. But ray-tree-based extension selection is quite difficult to implement, and position-based extension selection is essentially just the "seen by observer" mode. (A related discussion is #157 (comment))