Ordinarily in photography, shutter speed could be used to adjust the exposure. A long shutter speed allows more light to enter, and a slower shutter speed can darken the exposure. However, for video our shutter speed is not as flexible because it affects the fluidity of motion in our video. So we’re left with ISO and aperture to help us obtain the correct exposure.
What’s great is our DSLRs come with a built in light meter so your camera can evaluate if you’re at a proper exposure. DSLRs have made things so much more easier that finding the right exposure is more like playing a video game, where the object is to line up the pointer in the middle of the screen by dialing some knobs and pushing some buttons. Ok well, it might not be quite so simple. Canon cameras come with an exposure level with a moving index mark. As you make adjustments to the aperture, ISO, or shutter speed, the index mark moves accordingly to reflect the exposure level. When the index mark is matched up under the 0 arrow, your camera perceives the image to be correctly exposed. If the camera thinks the image is underexposed (too dark) the marker line will be off to the left. Too bright, and the marker will be off to the right and you’ll need to adjust your aperture or ISO.
Adjusting the Exposure
For beginners, you can start out with exposure compensation and then come back here when you’re comfortable with the whole process. For those of you who like control you can manually adjust the exposure. If your image is underexposed you can either increase your ISO and/or open up your aperture. However, either one comes at a price. Increasing your ISO could introduce noise (we’re talking about graininess here and not audio) into your footage. On the other hand, opening up your aperture (bringing the f number down) will change your depth of field. It’s up to you as the cinematographer to find the right balance and compromise. Now, if the scene is overexposed you can lower the ISO and/or close down the aperture (increase the f number). If you’re new to the whole process you might want to check out my exposure cheat sheet to get you started.
There may come a point where you’ve pushed your ISO all the way down but the scene is still overexposed. But you don’t want to change your aperture because you like the bokeh at that aperture. What now? Filters are the solution to our problem!