STOP is the word used to measure the change in amount of light in photography. The Exposure , ie the amount of light captured in the image sensor is addressed in STOPS.
A change in one STOP means the amount of light has been doubled or halved.
In photography Exposure( the amount of light captured in an image) depends on the three factors Aperture, Shutter speed and ISO. Each of these factors have a numerical set of values as measurement. A change in the value is addressed in STOPS and refers to the change in amount of light.
Let us look at the STOP value changes in Aperture, Shutter speed and ISO available in your camera. There is full stop values and in between the full stop values there will be the 1/3 stops. Before you read further , we assume that you have knowledge of Aperture, Shutter speed and ISO. We will now look into the full stop and 1/3 stop values !
Full STOP values
A full stop change in exposure means the amount of light is doubled or halved. Let us look at the full stop values of Aperture, Shutter speed and ISO :
- Aperture values : The values are called f-numbers and below is the sequence of values of aperture with 1 Stop difference:
- Shutter speed : range from 30 seconds to 1/8000 of a second.
- ISO speed in full stops range from 100 to 6400.
Also there are extended values below 100 and above 6400 in some of the advanced cameras.
So when you change camera settings from one value to the adjacent full stop value, the exposure of the image is doubled or halved depending on the camera settings.
⅓ STOP values
We have already read about the full stop value changes for Aperture, Shutter speed and ISO. Now we will discuss the ⅓ stop values, which is in between the full stop values in the exposure scale. These values will be available in your camera in between the full stop values for Aperture, Shutter speed and ISO. Let us look at them one by one with an example.
- Aperture ⅓ stop value: Let’s take the full stop values f4.0 and f5.6. In between the f4 and f5.6 you will be able to find values f4.5 and f5.0. These values are ⅓ stop values each. So when aperture value is changed from f4.0 to f4.5 it is a ⅓ stop change in exposure. Now when the change is from f4.0 to f5.0 , it is called a ⅔ stops change in exposure.
- The Shutter ⅓ stop value: We have shutter values as a measure of seconds or fraction of a second. Let us take shutter speed values 1/125 and 1/250 which is a full stop change in shutter speed. Let’s say we have set the shutter in your camera to be 1/125. Now when you try to adjust the shutter speed dial in your camera so as to make it 1/250 , you will notice that there will be shutter speed 1/160 and 1/200. These two values are ⅓ stops each. So when the shutter speed is changed from 1/125 to 1/160 its called as ⅓ stops change in exposure. Similarly when it changes from 1/160 to 1/200 , again from 1/200 to 1/250 , the exposure change is ⅓ stops.
- ISO values of ⅓ stops: If you check your camera ISO settings, you can find values getting doubled in full stop changes. In between two full stop values there will be two values representing ⅓ stops. For example we will take ISO values 200 and 400, we can see 250 and 320 which are ⅓ stops change in exposure. So when we change values from 400 to 320 , it is ⅓ stop decrease in exposure and similarly when we change from 200 to 250 it will result in ⅓ stop increase in exposure of the image.
From the above explanation of STOP values and their change in values you should now be having an idea of how the camera controls are to be utilized so as to change the Exposure in photography.