Shader Raycasting From Camera

Hi, I need to raycast from a secondary camera taking into account its properties (focal length, aspect ratio,etc) and then get the pixel hit in a shader for the main camera so that you can visualize what the secondary camera is exactly seeing. I hope the attached image is enough to explain the desired effect.
Thanks in advance!

Why not just add a hard dynamic spotlight placed at the same position and rotation as the camera?

You can generate a cookie that is the correct aspect ratio, then calculate the angle to match the fov.

You can then disable it when rendering on the projected camera Dissable lights per camera? - Questions & Answers - Unity Discussions