Still remember the examples of aperture values of f1.4, f2, f2.8, f4, f5.6, f8, f11, f16 & f22? How about the shutter speed values of 1sec, 1/2sec, 1/4sec, 1/8sec, 1/15sec, 1/30sec, 1/60sec, 1/125sec, 1/250sec, 1/250sec, 1/500sec and so on.. And ISO values of 100, 200, 400, 800, 1600, 3200 and so on.. Did you get the pattern for every stop of light as well? It should be yes because where moving on what we called the exposure reciprocals and make it easier to achieve the same exposure with the different values of aperture, shutter speed and ISO.
Let say that you've taken a properly exposed image with an aperture value of f8, shutter speed of 1/125sec and ISO 400. Using the reciprocals you may also use the values of:
Aperture f1.4 f2 f2.8 f4 f5.6 f8 f11 f16
Shutter Speed 1/4000 1/2000 1/1000 1/500 1/250 1/125 1/60 1/30
ISO 400 400 400 400 400 400 400 400
Aperture, shutter speed and ISO are parameters in creating an exposure. Each parameter can be adjusted to compensate the increase/ decrease of stop/s of light. In the example above you can see that if you change each parameter the other parameters can be adjusted to produce the same exposure but with a different perspective effect to your images. ISO can be also adjusted in the example above, if you need a shutter speed of 1/500 sec with an aperture value of f8, your ISO will be 1600. The shutter speed was decreased by 2 stops therefore you need to increase the sensitivity of your sensor by adjusting your ISO by 2 stops so that the exposure will be the same. The rule of thumb is whatever you decrease/ increase to each parameter, you should also decrease/ increase to other parameters equally to obtain the same exposure. Below is a video from Bryan Peterson, a photographer and an author who explains that you can create different images with the same exposure.
Understanding Creatively Correct Exposure with Bryan Peterson
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