Want to challenge yourself by shooting manually without a light meter? Head on over to eBay and pick up a Johnson “Standard Exposure” Calculator for less than $10. Released in the late 1940s, it’s a simple rotary device that lets you calculate the proper exposure by choosing the current scene, weather, exposure time, and film speed. Find more about these exposure calculators over on photomemorabilia. You can also check out the Exposure-Mat for a printable card that helps calculate exposure too.