I have talked in the preceding posts about three key factors in taking photographs, or “making an exposure”. These factors were the Shutter Speed, the Aperture and the ISO Sensitivity. For a refresher, you can click on each of these terms to re-load the respective post explaining the term in detail. Otherwise, I’ll assume you’re familiar with what each of these factors is doing to your final image, both in terms of how much light is let in or “detected” by your camera, as well as in terms of the effect it has on your final image.
This post is a first in a series that will look at the three factors again, focusing on how these work together. After all, if you want full control over your final product, you will need to have each of these factors under control, or at least working within parameters that you want these to be. To this end, this post will talk about getting a “correct exposure”, in other words – an image whereby the “right” amount of light has struck the film or sensor. In more layman terms, the image must look neither too dark, nor too bright – think Goldilocks for comparison purposes! How do we go about this? Read on…
First, we need to understand how to “read” our camera, as that will tell us when our settings (choices) will result in a correct exposure. You might have noticed that your camera can display a horizontal line with numbers written from left to right, typically going from say -3 to 3, with zero in the middle. On my Canon 70D (and pretty much on several other Canon DSLR models), the exposure meter looks like this:
That is an important gauge and one that you should be very familiar with if you want your images to look OK after you press the shutter. That gauge is the “exposure meter”. Think of it as a thermometer – instead of detecting heat, however, it detects how much light is going to be registered in the final image. If the camera detects that just the right amount of light is coming in, the meter will read zero (0). If less light is coming in than that needed, the indicator will be on the negative numbers, and vice versa. Your job to get the correct exposure is to get as close (or on) the zero in the meter. In most cases, at least. But let’s forget about the exceptions and the artistic choices – in general terms, that zero is good. But, what exactly is it telling you?
What the zero is saying is the following- the camera’s processor (call it its brain, if you wish) is showing you the result of a very quick computation that mixes together all the light coming in. Given that light carries different colours (in different degrees of brightness), mixing all these up leaves the camera with just one colour – much like when you mix together different paints. The result, with paint, is that you end up with just one colour of paint, and depending on the colours you mix together, that shade is either dark, light, or somewhere in between, right? Same happens with the light coming into the camera. When this is all mixed up, the camera knows that the correct amount of light for a “correct exposure” should result in one predetermined shade of grey – no pun intended here! Depending on how far off the resulting shade is, the exposure meter will show you a number that is either negative (for under-exposed, “dark” images) or positive (for over-exposed “bright” images), respectively. Therefore, if the grey is darker, you need more light to come in for you to get the correct exposure, and vice versa – if the grey is brighter, you need to reduce the amount of light coming in.
So, the next quetion arises – where do the three factors come in, in all of this? This question will be answered in Part 2 of this series, which will cover how we can manipulate one or more of these factors to get as close to the desired exposure, which, as hinted above, is generally the “correct exposure”, a reading of zero on the exposure meter that is.
So – let’s recap to conclude:
- The “Correct Exposure” is based on a calculation done by the camera that should give you an image that looks “right” – that is, neither overly bright nor too dark.
- There are circumstances where the “correct exposure” as given by the camera is in fact NOT what you’re after – but this will be discussed in later posts.
- An exposure reading on the negative side means your image is under-exposed – you need more light.
- An exposure reading on the positive side means your image is over-exposed – you need less light.
See you again for Part 2 and thanks for following my blog!