Fire in the Sky
Filming at night is difficult, but when there are unruly blasts of bright lights attacking your clean imagery, there are only few experienced videographers that are not going to have a problem. Filming fireworks can be great for your family reel or local promotional material, but if you do not do it correctly you can end up really damaging your project.
The first thing is you have to prepare your equipment and your camera. Get a good quality tripod with a rotating head that can move quickly and smoothly enough. This is so the camera will not shake the captured image when moving from object to object quickly.
Turn off all of your “auto” settings on your camera because these will just go haywire once the mock bombs begin flying into the sky. Something like auto focus would not know which one to focus on and almost all images would end up at least partially out of focus.
You may also want to use a wide angle lens so you can get in the most light as possible.
Dark Side of the Moon
What you are going to try to do is darken the image significantly so that you end up with a detailed pictorial of each fire web. To do this, you want to direct your camera toward the night’s sky and lower the iris to one of its lowest settings. This will likely darken out all stars as well as most of the ambient light from urban surroundings. You may even have to use Gain or an ND filter, but try to test this out by focusing in on a bright object in the dark ahead of time, like a lamp in a dark room or the light in a window from outside at night.
Retain Your Focus
Before the fireworks begin, try to focus in on an object that is far away but approximately below where the blasts will be. This can be anything, but the higher it is, the more prepared you will be. Focus in on that and you will have a better chance of getting each blast at that location and forward in focus.
When the fireworks begin, try to keep them in the frame and shut out most of the other objects. If you are getting things or people in the frame try to only get them from the backside. This is in attempt to minimize the amount of surface reflection and excess light that will alter your camera’s focus. Never allow any surface to reflect the light from the fireworks. Also try to position yourself so you are not getting any other type of background light from behind the fireworks.
You do not have to keep the camera faculties static during the whole shoot. There are going to be a lot of blasts and you can try slightly different angles and depths of view. Try zooming in and out a little. If you calibrated your zoom far enough this should not present much of a problem.