Shutter speed and Aperture relationship
The relationship between shutter speed and Aperture are polar opposites. When you change one in one direction you change the other in the opposite direction to maintain the proper exposure.
What is a shutter?
A shutter is a series of overlapping leaves that sits just in front of the cameras sensor and control the length of time the sensors is exposed to light. The faster the shutter speed the smaller the amount of time the sensor is exposed to light. These values can range from seconds to fractions of a second.
What is aperture?
Aperture is the opening in the lens that controls the amount of light that is allowed into the camera. F-stops as they pertain to the aperture can be confusing at first, but if you remember that the smaller the number the bigger the opening/aperture. Also remember that the smaller the number the shallower the depth of field.
Let’s say you have metered a scene and the proper exposure settings are going to be 1/250th second at f/5.6. Knowing this starting point allows us to build the below chart (at first on paper, latter with practice in your head).
|+2 f-stops||+1 f-stop||-1 f-stop||-2 f-stops|
|-2 stops of light||-1 stop of light||+1 stop of light||+2 stops of light|
If we stop down or close the lens opening from f/5.6 to the next highest number f/8, we cut the amount of light by half and therefore we need to slow the shutter speed down to lengthen the time that light has to hit the sensor. To do this we will need to change the shutter speed down from 1/125th to its next smaller number 1/60th.
If we stop up or open the lens opening from f/5.6 to the next smaller number f/4, we double the amount of light and therefore we will need to speed up the shutter to shorten the length of time light has to hit the sensor. To do this we will need to change the shutter speed up from 1/125th to its next larger number 1/250th.
Each of the above combinations will produce the same exposure; however they produce different depth of fields and motion.
Knowing this relationship will help you in extreme situations such as, night, snow, beach, open water, fog, rain, backlighting, high contrast ad dim light to name a few. In these extreme cases you will be able to change your settings up or down to maintain a proper exposure while allowing you to tell your story.
By practicing this technique you will begin to see the relationship and start making these changes intuitively while expanding your creative freedom.