6 - Focus finding

A lens brings collimated light to a focus, but where is that focus?
Surprisingly, aluminium foil can tell!

----------------------------------------------
Featured papers:
Visual speckle technique for alignment and centering of a translucent rough surface: doi.org/10.1364/AO.28.000722
(PDF version for free here:

Laser-induced damage threshold of camera sensors and micro-optoelectromechanical systems: doi.org/10.1117/1.OE.56.3.034108

Sorry for the bad audio quality. I tried a different microphone for this video but it clearly didn't improve the voice-over...

Optics,Alignment,Lenses,Mirrors,Lasers,Fibres,Waveplates,Infrared,UV,Light,Tutorial,Aluminium foil,