The long-exposure NR takes one shot when you push the button and then takes another shot - just as long - with the shutter closed and it subtracts what it gets from that 2nd exposure from what it got with the "real" exposure. That gets rid of a lot of the hot-pixels.
But you miss half of the fireworks show or lightning, or whatever, while waiting for it to do the 2nd exposure every time.
So one other thing you can do is to shoot with the long-exposure NR off and then do this:
Take one shot every so often throughout the show using the same long shutter speed and ISO. But shoot it with the lens-cap on and the aperture stopped all the way down.
Then, later, you can use Photoshop or whatever to subtract THAT single dark-frame from all of the neighboring similar shots. In effect, you've made one correction frame to use for a bunch of shots and you don't have to be annoyed by missing the best fireworks while waiting for the camera to make a dark-frame shot for each exposure.
Supposedly, you should make one of these "home made" dark frames for each ISO and shutter speed that you'll use and also any time the camera's temperaure changes significantly (whatever that means).
I guess for me, it's more agonizing to be missing the fireworks than it is to have some hot pixels. The "spot healing brush" in Photoshop takes care of those with great ease anyhow. And using the home-made dark frame method works quite well too.
But the in-camera long-exposure noise reduction does do a good job of eliminating the hot pixels. I just find it frustrating for lightning, meteor, or fireworks shooting because it always seems that I end up missing "the big one" when I use it
--
Jim H.
