Reciprocal Rule in Photography

What is reciprocal rule? (Reciprocity)- It is a law of a relationship between aperture and shutter. It stipulates that one stop increases in aperture is equivalent to the shutter duration doubling. Both increase light by one stop.

It allows to retain the same exposure or to balance but change either the shutter speed or aperture. When you use this rule, twice and much light coming in for half the time is equal to the same amount of light.

This is my activity to shoot an image and they need to use reciprocal.

Base: 

Aperture    Shutter speed    ISO 

F8             1/125               400

Reciprocal:

                               Aperture    Shutter speed   ISO                              

                            F6.3          1/200              400                          

Reciprocal:

                               Aperture    Shutter speed   ISO                              

         F10           1/80                400       

As you can see, the three images above are same but different exposure :)

Sometimes it's confusing because you need to know and to familiarize the exposure and a little bit of mathematics hahaha :)