Videography Tutorial – Exposure
In this series videography 101 we are going to dive into all the basic videography terms and tools for the beginner videographer, so let’s get started and today we take a look at what is exposure.
The term exposure refers to how much light is in your footage.
It could have a little light like the video on the right or it could have more light like the video on the left.
The camera exposure is set by three parameters:
- The sensors sensitivity to light or ISO,
- The shutter,
- and the Aperture.
Let’s start with the sensor sensitivity to light (ISO)
Your camera has a sensor. That sensor is what captures the light coming in from the lens and records that as frames.
The sensor could be more sensitive to light which will make the footage brighter or darker. You can change the sensor sensitivity to light (ISO) by going into the camera menu and move the ISO up and down and you will notice the screen becoming brighter or darker.
Different cameras have different ISO options, some, like the Canon beginner line cameras, will have ISO of between 100 to 1600 and some like the more advanced Sony A7S will have ISO of between 1600 to 409,600.
The higher you go with the ISO the brighter you footage is but high ISO also introduces noise into the footage as you can see here.
I can’t tell you at what numbers of ISO your footage will become noisy but as a rule of thumb, when shooting video you should try to leave the ISO at low numbers in order to prevent noisy video.
The second factor that sets the exposure for your video is the Lenses Aperture.
The aperture in simple words is the hole in the lens through which the light travels.
Without going into too much lens mechanics, your lens has blades that open and close when you change the aperture. The opening of the blades will permit more light to travel through the lens and hit the sensor and closing the blades of the lens will use less light to go through the lens and hit the sensor.
When you increase the aperture, the lens blades will close, and when you decrease the aperture, the lens blades will open up.
Depending on the camera and lens you are using you will be able to control the aperture form the lens or from the camera. In more advanced cinema lenses you will have mechanical control over the Aperture from a ring on the lens itself.
Another important factor for Aperture is the Focus plane which is – the size of the area the lens can focus on.
At high Aperture settings that focus plane is big, sometimes a few meters and sometimes up to infinity and at low aperture settings that focus plane is very narrow, sometimes up to an inch or two.
Here is an example, the footage of the right is with a low aperture setting you can see that the focus area is small. The footage on the left is with high aperture settings cause the focus plane to be big and mostly everything is in focus.
Now… let’s talk about the shutter.
The shutter is a little disk imprint of the sensor. That disk has on opened area and a closed area. The disk rotates infant of the sensor permitting light to travel to through it only in the opened area of the disk.
With different cameras, the setting will be different but in most consumer cameras you will see numbers ranging from 30 to 4000. These numbers means the fraction of time out of a second.
So 30 will be 30th of a second and 150 will be 150th of a second. The lowers the numbers the bigger the opening of the disco and the higher the numbers the smaller the opening of the disk.
At lower numbers, more light will go through to the sensor making the footage look brighter and at lower numbers less light goes through as the opening on the disk is smaller.
The lower the numbers and the bigger the opening of the disk the more blurriness will be introduced into the footage as the sensor is being exposed more time to each frame and the higher the numbers the sharper and more ‘video like’ the footage will be as each frame is exposed less time as you can see here.
The video on the left shot with lower shutter speed and the video on the right is with higher shutter speed. You can see that the video on the left has more motion blur to the moving object which gives it a dreamy look. on the other hand, the video on the left has a very sharp look.
The best setting to use regarding shutter speed is to double the frame rate. If you are shooting at 24 frames per seconds, you will need to set the shutter to about 48. if you are shooting at 60 frames per second, you’ll need to put the shutter on 120 and so on to achieve the best results.
One last thing that you have to keep in mind with regard to exposure is that if you are out in a sunny day and want to shoot your subject with a low aperture and have your shutter set to about 50 because you are shooting 24 frames per second then your video will look like that as you have too much light come into the sensor.
The solution for that is a natural Density (ND) filter. This acts as eyeglasses for your camera. all you have to do is mount it on the lens and adjust it as needed and you are done.