When you're working quickly one of the first things that gets left at home is a your giant complicated lighting kit. And if you're working outside unless you've got a Hollywood budget the only source of light you'll be relying on is the sun. Which is ok! When Hollywood does it, it looks something like this. But let's start small. Here's how to light an interview using just a camera and stuff around the house.
A natural light set up. - Spherical Image - RICOH THETA
The most important thing about any natural light set up is knowing where your main source of light is and how much light your getting out of it. If you're inside that source is going to be a window and if you're outside it's always going to be the sun. So for me the source was the large window behind me and the camera set up. I tried a few other set ups in the room behind my subject, but the light was fluctuating too dramatically as a result of the sun being covered by passing clouds. It goes without saying, natural lighting setups do not give you much control. Even for a Hollywood feature like The Revenant, you can only shape and manipulate the light that exists. No amount of money or gear will let you control the weather - keep that in mind!
The next step is controlling the light once you've picked a source. In the set up above the first thing I did was determine where to place to my subject relative to the window. The closer your subject is to the window the more light will hit them. The great thing about window light is that it's extremely soft. You're essentially diffusing the harsh sunlight through the window and as a result you got soft light that has a beautiful fall off. It also means the further you back your subject away from the window the less light hits your subject. So you have to factor the light ratio into your composition. In other words, you're going to need to place your subject somewhere that proves illuminates your subject and works for your framing.
Finally you'll need to adjust the amount of light hitting your subject with blinds/drapes/whatever to get it just right. The key is to have your subject be brighter than your background, but not so much so that your background goes black.
It really helps to have a camera with high ISO performance like a C100, A7S, etc... These setups can actually work great in situations where the room appears dark to your eye. The interview in this video is a great example of that.
The interview in this video was shot at ISO 8000 in front of a large window. I could've turned on a bunch of lights in the house and tried to raise the ambient level, but what I would've ended up with is a bunch of different colored light creating unflattering shadows. It was better to shut everything off and just use the sole window, because even though to my eye it looked too dark to my C100 it was totally fine. Sometimes the best thing to do when it comes to lighting, is start removing it.