Another concert. There was a theremin... actually a therasyn, which works by measuring the capacitance around its antennae and responding with tone and strength. You modify those capacitances by placing you hands near the antennae.
You might imagine such an instrument is sensible to stray magnetic fields, from say the lighting. You'd be correct. It was ISO25,600 dark and I was focusing manually, using whatever was bright enough to get a fix on: a small red led on the side of the theremyn, the sparkly bracelet on the pianist's wrist, plus hope and luck.
Anyway, lens flare can be cool