Distance setting of parabolic mirror is not intuitive
Three issues:
- focal length should be defined positive
- The distance that is applied during "connect_nodes" seems to be applied to anchor point of the parabola, and not the hitpoint. As the automatic alignment with oap shifts the parabola the actual distance is also altered. e.g. with two 90° oaps and a distance of 100mm, the actual distance is reduced to 50 mm
- If one wants to set up a parabola telescope it would be nice to set a distance according to the oap focal length. Maybe a helper function would come in handy.