Suyama Images | Reciprocals: The math of apertures and shutter speeds

Reciprocals: The math of apertures and shutter speeds

March 05, 2012  •  Leave a Comment
Aperture and shutter speed relate to one another and have an effect on the exposure of an image. If you put your camera into Aperture mode and select F4 your camera will select a shutter speed based on what it is seeing as the correct exposure. Change it to f5.6 and you will see the shutter move by the camera. The same with Shutter mode but it's reversed, it selects your aperture based on your shutter speed.
 
In Full Manual mode, you choose both aperture and shutter speed. 9/10ths of my photography and portraiture is in full manual mode, I like to be in charge. Knowing these numbers makes you the thinker but because of your understanding of them, you can tweak things to make an exposure a tad lighter or darker depending on what YOU see, not the camera.

Aperture stops:

1

1.4

2

2.8

4

5.6

8

11

16

22

32

45

64

90

128 etc

 

Shutter speed intervals:

etc.

8 minutes

4 minutes

2 minutes

60 seconds

30 seconds

15 seconds

8 seconds

4 seconds

2 seconds

1 second

1/2 second

1/4 second

1/8 second

1/15 second

1/30 second

1/60 second

1/125 second

1/250 second

1/500 second

1/1000 second

1/2000th second

1/4000th second

1/8000th second

 

Do the math:

F8 at 1/125th should be equivalent to F5.6 at 1/250 (or F4 at 1/500th, etc) in terms of achieving the same exposure.

F/11 at 1/8 of a second has the same exposure as 1/250 at f/2. It's just math, you open up the aperture you are adding light, adding 1 stop means if you want to keep the same exposure you can increase the shutter by one interval.

These reciprocals are important to know and understand in photography. The variable would be your ISO but for now let's assume you are keeping the ISO constant.

Here's a handy chart someone made up. You can download it, print it, whatever. But the important thing is to get to know it because being able to know these numbers will give you greater control and increase your possibilities. It will also help you with lighting and this will be covered shortly.  

equivalent exposure value chart


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