The correct exposure time can also be estimated with the help of an ordinary light meter, or one can build up one's own set of data by experimenting repeatedly with different light sources and using films with different characteristics.
精確曝光時間還可藉由一般測光表幫助推測，或在不同的光源條件下配合不同底片的特性反覆測試，建立屬於自己的一套數據。