As Bill Brown Says
The human eye is an amazing thing because it can adjust to all different kinds of light. You can adjust to dim as well as bright lighting with relative ease. Film and video are not that flexible: too much light will lead to overexposure and the loss of detail in the highlights of your video. Underexposure will result in a "muddy" looking image and likely have video noise.
The range of exposure for film and video is called latitude, and the idea is to try to make a scene look how you want it to within the confines of video or motion picture latitude.
In Bill Brown's chapter, he talks about light meter readings, because the crazy thing about shooting film is that you actually can't see your image until someone dumps it in a bunch of chemicals. That means you have to expose it correctly without seeing the image
Above there are a few light meters that are videographers and filmmakers use for either still or film photography. An incident light meter measures light that falls on the subject, so it is the most accurate in many situations.
A spot meter measures light reflecting off of a subject, but at tiny points. A meter like this can be helpful if you are trying to figure out if there is one section of your video that is over or underexposed. You can also use it to determine the f-stop range in a scene and correlate that with the latitude of your film or video camera.
A flash meter is kind of cool and is used by still photographers. You hold it up in front of your subject and point it back to the camera. While doing so, you trigger a flash to go off, and the meter tells you how to adjust your exposure properly on your camera.
The primary meters that you have to know about are reflective versus incident light meters.
A reflective meter is pretty much what everyone has in their camera. Even if you are using a camera that has all auto settings, it is still measuring light that is coming from a light source and reflecting off of your subject and into the lens.
So, why aren't these cameras as accurate as incident light meters? It's something called middle grey.
What you see above is a photo student using a grey card. All reflective meters have an internal reference point for determining exposure. The easiest way to look at it is that they see everything as middle grey. That means if your light meter is measuring light reflecting off something else, then it won't be a proper exposure.
For instance, if you use a reflective light meter to measure light reflecting off of a white shirt it will see it as middle grey and underexpose your shot. If the photographer would have used a gray card like above, then the shot would have been properly exposed.
So instead of seeing the white shirt as a highlight, it sees it as gray, so the image is only made up of all of the shades from 40% to the right.
Conversely, if you meter off of a black pinstripe suit, it will read it as middle grey and overexpose your shot. The grayscale of this shot goes from about 40% up to white.
So that's why people use incident light meters because it cuts out the middleman. (Middle grey man?) OK, that was weird.
If you have it handy, pick up your smart phone and turn on the camera.
- Hold it up to something with black in it and tap on that black object and you will likely see an overexposed image.
- Tap on something white and watch the image get too dark or underexposed
Your smart phone is metering off of either white or black and it is seeing it as middle grey.
Bill Brown gives a great example of metering in a difficult situation and some of the fixes he would use. What happens if you are shooting a scene and you have one character in the shade and another in the sunlight? You figure out based on your meter reading that if you expose for the person in the shade, then the person (or robot) is overexposed. Bill Brown gives three possible fixes:
- Split the difference (choose an f-stop in between the two exposures) If your film or video camera has enough latitude then you may end up with a decent exposure
- You could use a reflector, a big piece of material or cardboard that can reflect some of the light back onto the person in the shade.
- Probably the easiest solution would be to find a location where the light is more even on both of your subjects.