AS we all know, photography is all about controlling the light. How much light you let in. Depending on situation, you either let in less light or more light. And you can do that by controlling the main three exposure controls and they are (Aperture, Shutter and ISO). Now you can see how confusing it can become when a photographer want to explain to someone the amount of light he/she let in by having three different ways of doing it. And for this, the terms “STOP” came into existence.
So for example instead me saying sentence such as “ I have allowed twice as much light by reducing my aperture value from 2.8 to 2. Or I have reduced the light by half by increasing my shutter speed from 1/500 to 1/1000”. All this I can say it by one word, which is STOP.
So I can easily say I have increased my light by one stop or two stops etc etc. Or reduce my light by one stop, two stops etc etc. So how does STOPS relates to Aperture, Shutter and ISO. Simple and here is how:
– Aperture is valued internationally in this sequence (0.95, 1.4, 2, 2.8, 4 etc – See Figure). So if you go from 2 to 2.8, i.e. you have reduced the light by One Stop and same thing if you go from 5.6 to 8 you have reduced the light by ONE STOP and from 11 to 5.6 you have increased the light by TWO stops and so forth and so on.
– Shutter is the same concept (See figure). So if you reduce the shutter from 1/125 to 1/60, meaning you allow more light in, so you have increased the light by ONE Stop and so forth and so on.
– Same with ISO (see figure). If you increase your ISO from 400 to 800, it means you have increased the light by one STOP and so forth and so on.
They key thing to remember and accept here is that Aperture, Shutter and ISO are arranged in a fixed sequence and its there in most camera. There is a formula that dictates that sequence, but I won’t be talking about that formula here today. You just need to accept and memorize that sequence, as shown in the Figure.
So now, you should be in position to talk in STOPS of which it more or less summarize what you are trying to do in terms of light. So if you tell me that I have increase the light by ONE STOP, I don’t need to bother to know how you have done that, you may have done that by using Aperture, shutter or ISO. But as far as I am concern it only matters to me and you that you have increased it by ONE STOP.
I hope this is clear, go through the writing again and refer to the figure, is very easy really and if you have any questions let me know below. Thanks