I thought I would share may photography experience with you in regards to shooting fireworks. I tried about three different techniques last night, seeing what would work on my camera, and what does not. So I tried several different combinations with my Sony A77ii, and found some really weird issues. Remember, your are shooting at night, so longer exposures, are kind of what you are going for.
So, what worked: Setting the camera into Manual Mode, adjusting the focus to infinity, and shoot with an ISO of 100, at f1.4, using a wide lens, like 28mm. With this set up, I found that anything from 1.5 to 4 seconds worked great for the actual fireworks. Anything longer, you just get a bunch white light with little detail. The low ISO gives me little noise, and the wide open shutter lets in as much light as possible, and focusing to infinity, makes sure everything is in focus. And the most important piece of equipment, besides the camera, is a good sturdy tripod. I more or less played around with the exposure times, by programming it, and then using my 2 sec. timer for the shutter release, so to avoid camera shake.
What did not work: Using an high ISO, and setting the camera to Auto. None of the camera’s Auto functions would give my anything close to what I wanted. Even in Aperture Priority Mode, the camera was unable to focus and set the correct exposure as the fireworks were going off.
So setting everything to Manual Mode, including the Focusing, is obvious, but playing around with the exposure seemed to yield me a best verity of results. To long if an exposure, you get white light and too much “busy” in the shot, and to short, you seem to lose the brilliance/volume of each explosion. And fireworks are really unpredictable, unless you are the one setting them off. So every shot is basically a surprise. Also, every camera seems to be different too, I noticed. The guy across from me (Canon) was shooting in manual mode too, but his exposures times were a lot longer than mine, but getting somewhat the same results.
Anyway, I hope this helps you.