The numerous articles out there that are specific to a small majority of shots that the majority of sound ops will never encounter is staggering. What the average sound op needs in day-to-day productions on corporate, industrial, documentary, behind-the-scenes and news-type shoots is a basic understanding of shotguns and useful techniques that work.
Simply enough, recording "on axis" by pointing the mic directly at the sound source will give you the most gain (volume) and maximum cancellation of ambience that a shotgun mic can produce. So, if you point the mic at the talent’s mouth, the voice will be loud and the ambience will be pushed back. That’s what most of us have been taught—but it’s not how it should be done on almost all video production today.
Recording on axis is a technique for feature films that are slow-moving, scripted, blocked-out, rehearsed and followed by multiple takes. This technique yields poor results for the majority of run-and-gun-type shooting situations that most location sound operators work in. There’s not a snowball’s chance in hell you’ll be able to nail an unscripted group chatting away, a multi-person interview or a made-up, on-the-fly scene booming this way. When you have no idea who will say what, you need a booming technique that will give you the best chance of recording intelligible quality dialogue. That’s something I call the "lobeing technique."
Lobeing is when you point the axis of the mic’s pickup pattern at the talent’s sternum (the chest for those anatomically challenged) while still keeping the talent’s mouth in the lobe portion of the pickup pattern. This mitigates tone and volume changes to the voice when unexpected head turns occur. When recording multiple talkers, use the lobes to engulf the talkers and move the axis more toward the softer-spoken talkers to even out volume. I use the lobeing technique all the time. Very rarely do I record "on axis" and point the mic at the talent’s mouth. Even for sit-down interviews, lobeing yields a more consistent tone and volume.
For motion shots, lobeing is an absolute must. Since the lobe is the largest part of a shotgun’s pickup pattern, there’s less chance of missing when you or the talent start moving. Watch how people move while they talk. Notice how much more they move their head as compared to how much they move their chest. By keeping the axis of the pickup pattern focused on a single surface, the tone of the voice and the ambience are more consistent. The lobe engulfs all unexpected head turns so you’re not chasing them with the mic.
Now, regarding how closely you need to boom the talent, again, the "this is how it’s done" technique needs some updating. I was told in my film days as a boom op to get as close to the top of frame as possible without getting the mic in the shot. The bigger the shot, the longer the shotgun you’ll need to record quality dialogue. Well, again, this doesn’t really apply in today’s video world. How closely you boom isn’t dictated by the top of frame or the size of the shot, but by the perspective of the framed shot.
If the framing is ECU (extreme close-up), you want it to sound like the person is standing very close to you. The sound should be warm with noticeable bass in the voice and the ambience should be minimal. If it’s a medium-framed shot, create that perspective with sound by booming from farther away. You want the ambience to increase a bit and the voice to thin out for less bass. I’ve had close-ups where I boomed from more than a foot off the top of frame with a short shotgun to add more air to the shot, so it didn’t sound like talent was sitting on my head!