Exposure is, in my opinion, the second biggest thing you need to know how to accomplish properly when shooting. The first being composition and you can read more about that in my article The Angle of Your Dangle.
Shooting in an automatic mode on you DSLR or video camera is not something I’d suggest, however if you’re using a consumer camcorder, many times they will not have manually adjustable features. In an automatic mode, many times you will blatantly see the auto-exposure adjustments being made in the shot by the camera. Now, of course, there are exceptions to this, especially in a budget-film situation. One example is going from a shot out a window on a bright sunny day to an interior shot of a guy sipping his coffee. In a high-production scenario the light would be mitigated with more interior lighting and diffusion on the window.
ISO is the first form of exposure we will talk about. ISO stands for the International Organization for Standardization and this mostly means jack to us because it was created back in the days of film and had to do with film speed. Unless you went to film school and know how to shoot with film cameras and/or have an enormous budget, you won’t be shooting with film.
What you do need to know is what the range of ISO numbers mean. Basically, the higher the number, the more light you will let into the sensor, it will be “brighter.” The lower the number, the less light you can let in. The caveat is that the higher you go in number, the “grainier” the image will look; it will lose sharpness. There are optimal ISO settings for certain cameras and most Canon DSLRs work best around 800 ISO.
Different models of cameras have different ISO ranges. Know what range your camera has on it and how far you should push it.
Shutter speed plays the second role in exposure. Put simply, there is a mechanical door that opens and closes every time you snap a photo. This door, the shutter, can move faster or slower depending on your needs for the shot. The faster the shutter speed, the better you will be able to capture fast-moving objects without any blurring effect. The slower the shutter speed, the more blurring and “ghosting” you will get.
In sports photography they always use higher shutter speed to “freeze” the action in the image. In many time-lapse applications, you “roll” the shutter by slowing it down to get some blurring to avoid a staccato look.
In addition to speed, light allowance for shutter speed follows the opposite rule of ISO. The higher the shutter speed (i.e. 1/1000), the less light is let in and the lower the shutter speed (i.e. 1/60), the more light is let into the image.
Aperture, also called f-stop or Iris on true video cameras, is the final setting you must know to get your exposure correctly set. If you look down the barrel of your lens you can see a star-shaped hole. It’s made up of six overlapping blades that create the star-shape. This “hole” can open and close to various diameter sizes. When the aperture is fully open, more light comes in. When the aperture if closed, less light comes in.
Again, the light allowance rule is opposite of ISO. The higher the aperture (i.e. f/22) the less light is let in and the lower the aperture (i.e. f/2.8) the more light is let into the image.
The sole function of the aperture is light allowance. Now different lens have different aperture/f-stop capabilities. The lenses that are “faster” than others have a lower aperture/f-stop ability (i.e. f/1.4).
Knowing these functions forward and backward and how they apply to your shooting situations is key, especially when shooting guerrilla style. Which happens a lot in adventure filmmaking. Practice up and happy light-letting!