Now that we’ve talked about aperture, shutter speed, and ISO, it’s time to think about achieving balance. The Tao of using our cameras, so to speak.
To achieve what your camera considers to be correct exposure your aperture and shutter speed need to balance to let in enough light to expose your image. The exposure is the image created by the light entering the camera and being recorded onto the digital sensor. Most cameras these days have a built-in meter to give you the correct exposure.
Yes, your camera gives you the correct exposure but you still have choices to make. Remember your f/stop controls the depth of focus and your shutter speed controls movement.
(depth of field/focus)
4 4.5 5 5.6 6.3 7.1 8 9 10 11 13 14 16 18 20 22 25 29 32
60 80 100 125 160 200 250 320 400 500 640 800 1000
ASA/ISO 100 200 400 800 1600
All the numbers in bold are considered full stops. The f-stop, shutter speed and ISO go hand-in-hand to set the correct exposure. The meter tells you what the light in the room is and you manipulate the f/stop, shutter speed and ISO to give you the look you want.
Stay with me now. You may need to refer to the guide above. If your camera meter reads ISO 400, f/8 @ 125. This is a great standard exposure. But what if you are photographing someone running. 125th of a second won’t stop the action. Your runner will be blurry. You need to increase your shutter speed 2 stops to 500 but if you go up on your speed you have to go down the same amount(2 stops) on your f/stop so the exposure is still correct. That means now your exposure is ISO 400, f/4 @ 500.
So now let’s do a hard one. Your meter reads ISO 400, f/8 @ 125 for a group shot of 20 people. You want 2 stops more depth of field so that’s f/16 but you can’t shoot people 2 stops less 30th of a second because you will likely get blurry people. So how do you make this work? That’s right you change your ISO 2 stops. So your exposure is ISO 1600, f/16 @ 125.
Give it time and practice, practice, practice.