This was taken on Blackpool beach, facing north towards Fleetwood, at around 9pm last Friday evening. We'd been down on the beach photographing this year's International Fireworks competition (which was a bit disappointing in comparison to some of the other display's I've seen in recent years) and then decided to hang around and do some night photography.
If you've already taken a look at the original you'll see that a) I used two images, and b) that the final version is quite different to both of them.
I did plan on shooting this as a single frame (the image on the left) but the sky in the upper-right section ended up being very bright and featureless. The reason for this is that the clouds were drifting across the sky during the two minute exposure (f/5.6, ISO 100). The other shot started out as a test image, taken to calculate the exposure time I'd need for the longer exposure. There are different ways to do this, but I typically shoot at f/2.8 and ISO 6400, and then work out the exposure from there. The benefit of doing this is that you can easily calculate the exposure you need, but you can also check the composition (often difficult when it's very dark).
So, the exposure for the test shot was 0.6s at f/2.8 and ISO 6400, which translates to 2 minutes at f/5.6 and ISO 100.
Anyway, to cut a long story short, the sky looked better in the test shot, but the detail in the lower section was compromised through shooting at f/2.8 and ISO 6400, so I merged the two and then noise reduced the sky from the test shot. I also changed the white balance of both shots (to almost blue), tweaked the contrast, then added shifted the saturation and tone to produce a darker, colder shade.