Controlling Exposure in Photography

How do we control exposure in photography?

Exposure is controlled by 3 things:

  1. Shutter speed
  2. Aperture
  3. ISO

These all work together to control the amount of light that is recorded by your digital sensor. If we decrease one, we can compensate by increasing another.

Lets look at an example to demonstrate this relationship.

If we take the images above and start at 1/60th second as properly exposed. Lets say the the aperture is f8 and the ISO is 100. Lets not worry about ISO at this stage, so we fix it at a constant 100.

Properly Exposed Image

Properly exposed:
T=60
A=f8
ISO=100 (fixed)
T = Time = Shutter Speed
A = Aperture = Size of the Aperture/Hole


Lets say we increase the shutter speed to 1/125th second.
This means the shutter is open for half the time, therefore half the light enters the camera.
This will under-expose our image by 1 stop, because less light is allowed to enter the camera.

Under Exposed Image

How can we compensate for this under-exposed image?

By opening the aperture by 1 stop, which will let in more light (bigger hole).
So we increase the aperture hole from f8 to f5.6, (have a look at my diagram below, notice the bigger hole).

 

Properly exposed:
T=125 (was 60)
A=f5.6 (was f8)
ISO=100 (fixed)

What did we do here?

We increased the shutter speed (1/60th sec to 1/125th sec), thus decreasing the light that enters the camera.
To compensate for less light, we opened the aperture more (f8 to f5.6).

Can you see how aperture and shutter speed work together?

This also works the other way around too.

If we decrease the aperture (size of the hole), we will need to increase the shutter speed (increase the time that the shutter is open, and lets light onto the sensor) to compensate.

Make sense? If not then read it again, or comment below.

 

Next we look at histograms.

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