CALCULATE LONG EXPOSURES
It’s important to ensure that you know what image you’re going to end up with after a very long exposure. Save time by working with shorter exposures, then calculate the correct long exposure time
1 EXPERIMENT WITH SETTINGS
Use relatively short exposures (30s or less) and high ISOs (3200 or more) to gauge the light. If you feel that your image is too dark, increase the exposure time or the sensitivity, or make the aperture larger (a smaller f-number).
2 TAKE SOME TEST IMAGES
Working with shorter exposures saves time, as you are establishing what levels of light your camera is capturing. Check back on the image review screen and adjust the settings until you are happy.
3 WORK BACKWARDS Now reduce your sensitivity by a stop (say 6400 to 3200). At the same time, double the exposure time. Keep doing this until you get to a low ISO number (400 or less) and a long exposure time (four minutes or more).
4 LONG EXPOSURE NOISE
REDUCTION Make sure that you turn on LENR. Once the shot is taken, the camera will take another shot with the mirror down, working out where the hot pixels will form and removing them from the final image.
5 WAIT FOR THE IMAGE If you’re confident in your settings, you can pack your camera away, without turning it off, and go to your next location. However, it may be worth staying until the camera has performed LENR to make sure everything is okay.
6 CHECK THE SHOT If you’ve waited a long time for the image to be processed, it is worth checking everything is okay. Zoom in on the image, make sure it is in focus, and check that the camera hasn’t moved during the exposure.