Lens drawings and incorrect ray paths.

Question

Why don't my lens drawings show the correct ray paths?

Synopsis

Solution

1. You have entered your data incorrectly. The lens drawings prepared by OSLO are primarily intended to give you a visualization of how your system performs and if that data is incorrect, the graphics may not produce the visualization you expect. Check the magnitudes and signs of all data, including the lens drawing conditions (Accessible via "Lens>>Lens Drawing Conditions") for errors.
2. OSLO does not have the capability to draw your system, or some element of your system. In this case, it may be that the ray trajectories are actually correct. OSLO is a numerical analysis program, and can correctly analyze lots of systems that it can't draw. If you need to have a drawing that includes a non-standard geometry, you can use bdi data, or the internal 3d drawing commands, to attach a drawing to a surface.
3. You are not looking at what you think you are looking at. You might be looking at the virtual extension of a ray, rather than the ray itself. This commonly happens when the user places a folding mirror in the system but keeps the thickness of the mirror positive forcing OSLO to trace the ray behind the mirror. This is not "incorrect" behavior because OSLO is simply tracing the virtual ray as opposed to the real ray - but the result may look unexpected to you.