The problem with understanding aperture, exposure, f-stops, shutter speed is that you need to think on 3D.
Yes, 3D. And no, I’m not nuts. Just imagine three separate levers that will control how fast a bucket gets filled with water.
Try to imagine you need to fill in the bucket with a determined amount of water. You keep the funnel open too long and it will overflow. You shut it down too soon and it won’t be filled enough. The same for the funnel size, too small and it won’t let water go through easily and will take much longer to fill the bucket. You open too much and it will fill the bucket to fast.
Replace F-stop with the size of the funnel, shutter speed with how long we’ll keep the funnel open and light for water. You’ll have the exact same challenge, set the correct amount of shutter speed and f-stop to obtain the desired exposure.
Because a picture is worth a thousand words here is one…
Now is when the triangle comes into picture. And no, it’s not a 3D triangle.
At this point you’ll probably deduced that both settings are inversely related, more shutter speed-less aperture=correct exposure. And less aperture-more shutter speed also=correct exposure.
So, why a triangle? Because we also have sensor sensitivity. This is similar to the volume knob in your stereo, only it increases or reduces sensitivity of the sensor. If we make the sensor more sensible to light it will require less shutter speed or allow for a smaller aperture. Hence the triangle.
Sensor sensitivity is measured in ISO. This is because we photographers are very nostalgic and we carry on using the same term as in film photography. will require less shutter speed or allow for a smaller aperture. Hence the triangle.
There are some considerations when setting these three parameters, each one has a different effect on the picture which we should understand.
Too slow shutter speed (below 1/60 handheld) will cause blurry shots. Too small aperture will have a very shallow DoF reducing the focus area dramatically. To high ISO will render pictures with a lot of noise.
One way to simplify our lives is to decide to set one parameter to a fix value and play with the other two to obtain the desired, not always correct, exposure (after all we ARE artists). Lets say I want my pictures with very low noise, I would set ISO to 100. Next I’ll decide on shutter speed and aperture depending on the type of shot I’ll be taking. If it is a portrait I will want to blur the background then I’ll set a big aperture and modify shutter speed to obtain desired exposure. If, on the contrary, I’m shooting sports I might want to freeze the action setting high shutter speed and modify aperture to also get the desired exposure.
Have you noticed I’m not using the word “correct” when I describe exposure? There’s not such thing as a correct exposure. Well, it is but is all mathematical and ruins the art side. I believe the exposure is a result of your vision as photographer. You see and interpret light and use your tools to render a picture that will reproduce your vision. And this is the tricky part. Not the math, the numbers, the histogram. Nope, it is to learn the limits of your tools, to experiment long enough so you’ll develop the ability to express your vision. An in this process you will be braking all rules.
Well, I ranted enough for this article-less blog. I hope you enjoyed it!