I purchased a really cool device from someone through eBay this week. It’s a light meter for photography from the fifties and it’s fully functional. Cost me $12.00 total. Modern light meters can be had for $250-400 for standard ones, more for super good ones.
There’s a light sensor on the top (behind the little trap door thing) that collects the light. This then moves the little red needle which points to f-stops. The bigger, gear-like, dial is twisted so that the number displayed in the meter lines up with the “Open” mark (because I have the trap door open). The smaller dial is set to my film speed. I then have the proper shutter speed matched to the possible f-stops and I’m on my way to a perfectly exposed shot.
The meter is very small too. Truly pocket sized. It doesn’t take any batteries and comes with a tiny leather case. Sweet deal!