Fireworks are one of my favorite subjects to try and get creative with. I typically don't have much of a systematic approach and generally just use bulb mode with manual exposures and keep shooting until something looks nice! This is a real huge advantage of digital, where you can get immediate feedback and also not worry about burning through film.
For this shot, however, I had just read about a fascinating technique that involved altering the focus during the exposure. It took several tries, but this was by far my favorite shot of the night. I set up my Canon 5D IV on a tripod with the 17-40mm lens pointed in the general direction of a nearby fireworks display and readied my wired remote trigger. I would follow the path of each launch and trigger the shutter right before detonation, holding it down for an arbitrary amount of time to make sure I capture the full bloom (and keep it in frame). This part was the key, however: I pre-focused to the nearest distance the lens allowed and manually turned the focusing ring to infinity during the detonation, trying to be as smooth as possible while timing it just right. This particular exposure was 1.8 s at ISO 160. I used the widest aperture (f/4) to make the bokeh effect at the beginning of the exposure as strong as possible.
I honestly couldn't believe my eyes when I saw the rear screen after this shot--somehow it had all come together just right! You can even see at the very tips of the trails where focus went just beyond the plane of the fireworks, adding nice little frills to the tips of this fire flower's "petals." I've taken plenty more photos of fireworks since this one--mostly more standard (i.e. boring), some more abstract--but this was just the perfect balance of each for me!
