focal length depends on the angle of view you want to capture and that of course depends on how far you are away and how big the display is

fireworks are quite bright but in order to capture streaks instead of bright dots you need long exposures

you need a tripod (yes you can do some hand held work but to get really good stuff a tripod is nessecary)

A remote release would be good.

Generally what you want to do is to shoot at say F8 or F11 or so.

Shutterspeeds should be long. 1, 2 or 3 seconds. Use bulb if you have a remote release.

Try not to get something very bright into the picture otherwise it will overexpose

Now when something goes up you start the exposure until at least one is finished. Generally you want to combine multiple pops on one frame. Dont do too many though

Anopther option is to go to long exposures and use something to cover the lens (black baseball cap). open up when you want to expose, close when you do not want.

Then there are all kinds of neat tricks such as combining the fireworks with background stuff, using flash to manually illuminate people or things in the foreground,...

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Michael Salzlechner
http://www.PalmsWestPhoto.com