Correct Exposure | an endless conversation
Sometimes trying to achieve the best exposure in your photography can drive you mental while you fight with the various settings wandering what should be where.
In this article I want to give you a very basic understanding of how you can achieve the correct exposure in your pictures.
There are two key elements that work together in a variety of combinations to let the right amount of light into your camera. Your SHUTTER SPEED and your APERTURE.
These two elements act as the guards standing at the front of the castle and restricting access to the king inside the castle (your SENSOR.)
Just a brief comment on the SENSOR:
Your sensor takes the light that is flowing into your camera and converts that light into a picture. The more light that flows in – the whiter/brighter your picture is going to be. The more the shutter and aperture restrict the light coming in – the darker your image will be. If the sensor isn’t given enough time to gather light then it is like trying to build a puzzle without all the pieces – the sensor will just fill in the missing pieces with a black square. If you leave the shutter open for too long the sensor will try and build a puzzle with too many pieces and will just start to layer those pieces on top of each other, the more pieces of light the camera puts on top of each other the brighter and brighter the puzzle will be at the end! (a brilliantly simple but detailed explanation of how the sensor works can be found here.)
Your SHUTTER SPEED
The shutter acts like the front door to your camera. When it opens, light can flow inside like a welcome guest, the longer the door is open – the more light can flow inside the camera and onto your sensor.
The shutter is very simple to understand: leaving the shutter open for a longer period of time with a longer shutter speed will allow your camera more time to gather light. Leaving the shutter open for a short period of time with a short shutter speed will only leave a short moment for the camera to gather light.
On a bright sunny day outside in the garden, there is plenty of light in the environment which means that your camera isn’t going to need a lot of time to gather light – so a shorter shutter speed is ideal (around 1/250 + should do it)
But on a cloudy day photographing indoors, the lighting is dim and your camera will need more time to gather what little light is available in the environment. Setting a slower shutter speed is going to give your camera more time to send light to the sensor so that it can be translated into a picture.
If your shutter was an eyelid – think of your aperture like the pupil of your eye. When it’s dark or dim, your pupil will open wide to allow more light in at a time. If it is really sunny outside your pupil will shrink so that when your eyelid opens and the light hits your pupil, it is a small opening that the light has to go through to get into your eye, so less light can flow in at a time even thought the eyelid is open.
In your camera you have full control over the size of your pupil.
Your aperture is made up of 7 metal petals which interlap each other and fan in and out to increase or decrease the size of the aperture opening.
A small aperture allows less light to enter at a time, a big aperture will allow much more light to enter.
Numbers with your aperture can be confusing.
The size of your aperture is measured in F-stops (F followed by a number: F5 or F29 etc)
An aperture of F5 is a very wide open aperture. An aperture of F29 is a very small opening. Confusing I know because 29 is much higher than 5!! The reason for this is that 1/5 if much bigger than 1/29 (Yip! Fractions! Taking you back to your school days J)
F doesn’t stand for Fraction though – it stands for Focal. Your Focal ratio is measured in Fractions.
Note: these numbers are a guide and depending on the available lighting the numbers will need to change, but it will give you a good starting point when trying to find the ideal exposure in a given situation
Late afternoon at the park, the sun is sinking low and there is a light cloud cover. You have already taken off your sunglasses because the light isn’t strong enough to bother your eyes. What setting should your camera be on?
There is still some light in the air with the sun not all the way down yet, so a shutter speed of around 1/125 and an aperture of around F8 – should get you what you need. If it’s not right then slowly decrease your F-stop (widening your aperture opening) and then begin to decrease your shutter speed until your test shot shows the best lighting.
A very bright and sunny day outside would require a faster shutter speed of 1/500 and an aperture of F8 or higher.
So what happens when it’s dark, you can’t use your flash, your aperture is as wide as it can go and your shutter is as slow as it can go without causing blur?
Your only option now is to turn your ISO up. Note how I haven’t chatted about ISO until now. The reason for this is that it is not a key element in achieving best exposure. Even though it comes in handy at the best of times – your ISO is your last resort. Only start playing with your ISO once your aperture and shutter speed are as good as they are going to get. The reason for this is that a high ISO adds noise to your images which can ruin them. On a sunny day outside – your ISO should never be above its minimum setting. By default your ISO should live on its minimum and only go up when you need it to.