introduce function draw-mirror
add code for raytracing and find lens position on the polygon that gives the optical axis
figured out how to calculate the angle of the length. i should use atan2 to get rid of sign problems
i hoped to simplify the angle calculation of the mirror normals by calculating the angles of the polygons direction vectors using atan, but it doesn't look much simpler
display dichroic, objective and a mirror for the sample
calculate the ray intersection with the dichroic beamsplitter
do the reflection at dichroic and intersection with the scanning mirror (mirror 1)
send ray through the object and back to the scanning mirror
finish tracing a ray through the system, i just need to position a tubelens and camera now