You need three things that actually matter: to be there for the window, a camera that can do a few seconds of exposure with the flash off, and something that does not move. A remote or a two-second timer helps. Everything else is preference.
Timing
Look up the place and date on this site before you leave. Evening: be on the spot at sunset, compose, then wait for the blue. Morning: be there at the start of morning blue hour, in the dark. The useful part is short. I treat the calculator as the alarm, not as a suggestion.
The subject
Blue hour likes lights. A dark hillside against a blue sky is just a silhouette. Bridges, riverfronts, stations, harbours, a tower with windows, a street with wet asphalt — those hold. Watch the corners for a streetlamp that will flare, a pole that cuts the frame, a billboard that blows out. Walk two metres if you have to.
Tripod
At ISO 100 and a few seconds, handheld is a wish. Put the tripod on solid ground, hang the bag if it is windy, and do not extend the centre column. Turn off image stabilisation on the lens once the camera is locked down — on many lenses it hunts during a long exposure and softens the file.
Exposure
Manual is easier than fighting auto. A starting point I still use:
- ISO 100 or 200
- Aperture around f/8 (f/7–f/11). Higher numbers make spikes on point lights; too high and you lose sharpness and time.
- Shutter 1–8 seconds, adjusted until the meter reads about −1 to −2 EV
The camera LCD lies toward the bright side at night. If the sky looks medium-grey on the back screen, it is probably right. If it looks already deep blue on the LCD, you are underexposing and you will lift noise later. If you need more than a couple of stops of correction in the raw file, change the shutter next time rather than pushing the file.
Compact cameras: night mode or a long-exposure scene mode, flash forced off, exposure compensation around −1 if you have it. You will still get a usable sky if the camera can hold 4–8 seconds.
White balance
Shoot raw. Set a Kelvin value around 4000–4800K so the preview looks like the scene, then finish it later. Auto white balance at blue hour often goes magenta or too warm because it tries to “correct” the blue. If you are stuck on JPEG, lock a cloudy or tungsten preset and leave it for the whole series so the frames match.
Weather
Clear air or high, thin cloud is ideal. Low grey stratus kills the colour. Rain can be excellent after it stops — pavement turns into a second set of lights. Wind is the enemy of long exposures on bridges. Fog on a river can be better than a postcard sunset if you want atmosphere more than sky colour.
Take a frame at sunset (still warm), two or three in the middle of the blue, and one when the sky is almost gone. You will know which minute was the one.