What is a ‘Stop’ of Exposure in Photography?
In today’s episode I am going to explain what a ‘stop’ of exposure is and how knowing this can help you to expose your images quickly and accurately!
Well it’s been a while hasn’t it??!! Sorry for the long pause in podcast episodes. I have been super busy working on my Manual Exposure Masterclass which I just launched on Monday. You can find out all about it right here . But that is not what today is about. I am back with a bang and a whole list of new episode ideas!
So without further ado lets dive right into ‘stops’! You might have heard other photographers talking about stops and it is easy to think they are just talking about their f-stop (their aperture width). However, the word ‘stop’ in photography is not just used when talking about apertures. A ‘stop’ of exposure is, like everything in photography, all to do with light. So what is a stop of exposure?
Let me explain.
Every time you double the light coming in to your camera this is called a ‘stop’ of exposure.
So, for example, when your shutter speed decreases from 1/250 or a second to 1/125 of a second you have doubled the light coming in. That is one stop.
When you increase your ISO from 200 to 400 you have doubled the light. That is one stop.
When you widen your aperture from f/8 to f/5.6 you have doubled the light coming in. That is one stop. With apertures the numbers don’t double – they are ratios so it doesn’t work like that. We have to think of the size of the opening doubling. And opening from f/8 to f/5.6 doubles the size of your opening.
Same goes for halving the light. When you go from a shutter of 1/250 of a second to 1/500 of a second you have halved the light coming in. That is one stop.
When you decrease your ISO from 200 to 100 you have halved the light. That is one stop.
When you narrow down your aperture from f/8 to f/11 you have halved the light coming in. That is one stop.
So when you hear people referring to a stop that is all it means. Doubling or halving the light.
So why does this matter?
Well if you understand exposure stops then you will actually be able to make adjustments to your exposure settings very quickly and accurately.
That is because the dials that you use to adjust your aperture, your shutter speed and your ISO are linked to stops of exposure.
For example, if you turn your dial one notch and your shutter speed goes from 1/125 of a second straight to 1/250 of a second then you are working in whole stops. Every turn of your dial equals one exposure stop.
And guess what? That means when you are adjusting your aperture, every turn of the dial is also one stop. So when you turn it one notch your aperture either doubles or halves in size.
And yes you guessed it, same goes for when you are adjusting your ISO. When you turn your dial one notch to the right or the left you are either doubling it or halving your ISO setting. You are doubling or halving the light.
However, my camera dial doesn’t work in whole stops. When I speed up my shutter speed from 1/125 it doesn’t jump from 1/125 to 1/250. It takes me three turns of my dial to get from 1/125 to 1/250. Mine jumps to 1/160 to 1/200 and then to 1/250. My camera works in thirds of a stop. So every turn of my dial is a third of an exposure stop.
Some cameras will need just two turns of the dial. They might go from 1/125 to 1/180 to 1/250. A camera like this works in half stops. So every turn of the dial is half an exposure stop.
So here is the thing.
If it takes you one turn of your dial to double the light with your shutter speed then it will take you one turn of the dial to double the light with your aperture and with your ISO.
If it takes you three turns of your dial to double the light with your shutter speed then it will take you three turns of the dial to double the light with your aperture.
Now be careful in this scenario because it might be that it will take you three turns of your dial to double the light with your ISO too but with some entry level DSLRs it might just be one turn. You will know, of course, by simply turning the dial and checking how the ISO jumps so just be sure to check this.
You will notice that the numbers are not always exact halves and thirds. There is some rounding up and down used by camera manufacturers so don’t get hung up on this.
The important thing to understand is that a stop of exposure is the same regardless of whether you are changing your aperture, your shutter speed or your ISO.
So let’s put this into context
I am sure you are wondering where this is going. Let’s say you are shooting some fun portraits outdoors with a group. Let’s say you start with a very wide aperture to shoot individual portraits with a very shallow depth of field. You go through the process of metering the light and finding the perfect exposure and then you shoot for a while like this.
Now let’s say that the light you are shooting in has not changed at all. You are in the same location with the same light. But this time you want to group everyone together on some steps. Lets imagine that you use 10 steps to group your subjects so they are all at different distances away from your lens – some are in front, some are at the back and some are in the middle. There is depth to this image and you want everyone to be in focus so you will need a narrower aperture to increase your depth of field. So let’s say you narrow down your aperture from f/2 to f/8.
For me that would be 12 turns of my dial. Every turn of my dial is 1/3 of a stop so that means I have decreased my exposure by four stops. If every turn of your dial is one exposure stop then that would be four turns of your dial. Now it doesn’t matter whether your dial works in 1/3 stops or whole stops. All this means is that I can refine my exposure a little more. It is four exposure stops regardless of how many times you turned the dial.
Now if the light you are shooting in hasn’t changed then you know that all you need to do is add four stops of exposure somewhere else to balance this exposure.
So you might choose to add four stops of exposure using your shutter speed. If you narrowed down your aperture with four turns of your dial then you will simply need to slow down your shutter by four turns of the dial and that will give you the exact same exposure.
Maybe you don’t want your shutter speed to get any slower. Then you will simply increase your ISO by four turns of the dial and that will balance your exposure too.
Take a stop away here, add a stop there. Add two stops there, take two stops away here.
You are just balancing the light.
When I am shooting you will hear me counting away all the time. What I am doing is counting the turns of my dial so that I can just adjust my exposure quickly without having to meter the light again. Because if the light hasn’t changed then why should I have to right?
Give it a try!
I go into this much further in the Manual Exposure Masterclass but the difference with the masterclass is that all of the learning is reinforced with lots of practical tasks.
With the podcast you can listen any time you like and you can multi-task. The masterclass is still audio but it requires you to make time (20-30 minutes) and you must have your camera with you. You simply play the audio through some headphones and I walk you through practical exercises with your camera which really develop your skills in manual exposure. You can play, pause and rewind and just take everything at your own pace.
The masterclass is not for everyone, some people are just self-starters and like to find their own way around after undertaking some learning. However, some of you have told me that you need that extra practical coaching and I have listened. This is as close as I can get to being with you without actually being with you. After these nine practical sessions you will have a very sound knowledge of manual exposure indeed.
This is launch week so there is an introductory offer available until Sunday 20th December at midnight. It’s only $59 until then (that’s only £38 for those of us in the UK).
next week I am going to be talking about ISO again. There was a great question in the facebook community the other day about digital noise and I am going to share with you the secret to less digital noise in your images, even at high ISO settings.