[cesis]

There exists an entire industry for counting and sorting things(e.g. optical bean sorting).

There also are rather cheap optical tachometers(measuring rotations by applying reflective tape on rotating surface). I would guess such devices could also be tailored for counting falling objects.

And also there are multiple old- school tricks for similar tasks. E.g. if you need to count nails, weight them all, then weight a single nail, then divide the weights to get count.