Exposure is simply a matter of how dark or light a photograph is.
Too dark is termed underexposed, too light and it’s referred to as overexposed. Just right and it’s called even or neutral exposure.
In its simplest form, exposure is a function of three factors: shutter speed, aperture and ISO. We’ll go into these in more detail in a future post, but for now just know the following:
Shutter speed is how long light is able to enter the camera for.
Aperture is the size of the opening through which light enters the camera; the wider the opening the more light that can come in.
ISO is the camera’s sensitivity to that light. Making it more sensitive without changing either of the other two factors will result in lighter image.
Leaving out ISO for the moment, let’s just look at the combination of shutter speed and aperture.
The way I lie to think of it is to imagine I’m trying to fill a bucket with water. The tap I’m pouring the water out of is how I control the water. The wider the diameter of the hole the water is coming out of (Aperture) the more water can come out in a set period of time, and the longer that set period of time is (shutter speed), the more water will come out as well.
The next step is to set a specific amount of water I want (exposure). Let’s say we set that level to the middle of the bucket, and we’ll call this even exposure.
If I have a very narrow apertured tap, only a thin stream will emerge, and I will need to run the tap for longer to get the level to the middle, ie. I will need a slower shutter speed.
If, however, the tap’s aperture is very wide, I will literally only need to open and close the tap and a large volume of water will come out, thus reaching the desired level in a much shorter time, ie. a faster shutter speed.
I hope this is making sense so far.
If you’re following, it should be becoming evident that the same exposure level (water in the bucket) can be achieved in different ways; a slow shutter speed and narrower aperture or a fast shutter speed and wider aperture. Many combinations of the two will give the same end result.
In photography however, photographs are going to look very different depending on which option you select to achieve your desired exposure level.
A faster shutter speed will freeze the action, while a slower one will result in motion blur. Both are great, so long as you understand which is going to do what.
Most of the time in wildlife photography you are wanting to freeze action, so the wider aperture/faster shutter speed combination is best.
Lenses have a limit to just how wide their apertures can open though, which brings us to the third and final part of what is known as the Exposure Triangle: ISO.
ISO is a measure of your camera’s sensitivity to light. More sensitive means it can achieve higher shutter speeds. The trade-off is that the image quality will degrade slightly as the ISO is increased, but this is a price you have to pay to achieve fast enough shutter speeds to not have a blurry image.
“Trade-off” is the key thing to remember here, as the Exposure triangle – comprised of shutter speed, aperture and ISO – is a constant compromise between the three, in which one or the other is generally prioritised to achieve the desired result.
We’ll delve a little deeper into Shutter Speed, ISO and Aperture do in future posts.
Please comment down below if you have any questions about the subject, or would like to hear about any specific photography topic that is particularly relevant to safari.