I was curious whether it is possible to see a mirror reflection of caustics with BiDir renderer or not. In theory they should be there. In practice (viewtopic.php?f=16&t=8119#p79937
) it is recommended to use SPPM renderer. So I did the simplest scene I can imagine and render it in low resolution up to insane samples per pixel numbers. It was expected to see some caustics at 10^5 S/p. Here are the results.
P.S. The scene is illuminated by sun. So, if someone wants to see sun light caustics reflected in a scene one should aim for hundreds of kS/p in BiDir case.
UPDATE: SPPM produces good result almost infinitely fast compared to BiDir, but it is still a little bit blurred.