1. The problem statement, all variables and given/known data For self study, I've been trying to understand my convex mirror. Some online instruction I've been following states that if an incidence ray (red line in my model, below) parallel to the principal axis (black line) hits a convex mirror (full curvature outlined in black, centre C), the reflected ray (purple) extended back passes through the focal point (F). 2. Relevant equations In my graphed model below, the points & vectors are centre of curvature, C is at origin focal point, F = (25,0) normal to incident, N = (0.91128...,-0.41178...) incident, I = (-1,0) reflected, R = (0.66087...,-0.75049...) 3. The attempt at a solution I graphed my model (above) but the reflected vector does not run exactly through my focal point as expected. I've checked this is not simply a rounding error (or any other obvious mistakes). There are also other problems when I plot more incident vectors emanating from the same point (not shown): the reflected vectors do not converge on a virtual image point as expected. Something crucial is missing from my understanding of this problem.