We have always been impressed by images of star trails over static subject matter such as mountains. A couple of years ago we tried it in Yosemite as the skies there are good and dark, but our approach was amateurish and so the results were nice but not perfect. Our reasonably successful attempts in Lakeland a couple of weeks ago gave us the incentive to try again.
So, with the promise of a couple of clear nights and with a plan in mind for subject matter, we headed out into the black of night. 6 hours later, with feet covered in sheep dung and frozen fingers, the shots were on the card and confidence was positive. Results were ok but not ideal, so we did it again the next week.
We had one main issue - fogging up of our lens. Possibly this was due to the atmospheric conditions and time of night, and the second attempt did not suffer so badly from it : the temperature was close to zero and we went out after midnight. Even so, the one 'fogged' image that we have post-processed has some atmosphere when mono-toned!
We shot all images using a 24mm lens at f7.1/8 and ISO's between 125 and 800 to give exposure times of anything from 5 to 30 minutes. The main subject was a local windmill, which we had to light using a torch - a bit odd doing such a thing at 3am in the morning but that's the job. Frankly we were surprised the police didn't turn up.
We'd urge you to give this a try as the results are very satisfying! We'd love to try this with static unlit aircraft or other transport subjects as we like the idea of objects which are designed to move being static with the sky above in motion.
A few tips in case you decide to try this :
- these are long exposures. We initially shot high ISO test shots to gauge the exposure needed to balance star trails, depth of field and light needed on the mill before we attempted any longer exposures. So for any given shot, expect to take at least an hour setting up and getting your ONE SHOT.
- stars rotate around the pole star and the further from it the faster they move. So you can get away with shorter exposure times away from the pole. We shot 8, 16 and 30 minute exposures with the longer ones where the pole star was in frame.
- all images were shot using a 24mm lens but a wider angle may be useful, depending on the ground subject you use if any.
- using an aperture of f7.1/f8 provided depth of field for both the mill and sky. Sky only shots don't need this so shorter exposure times and higher ISOs could be used and the images stacked. If you do this you need also to shoot dark frames - this becomes a complex job and there are many references elsewhere on the web which can guide you on this. We've not yet tried it.
- take a powerful torch and a small one. Using a bright torch to fiddle with camera settings destroys your night vision. Ideally get a smaller torch with a red filter.
- have a couple of lens clothes to hand to wipe your lens in case it fogs up. We removed our UV filter, which may also help. If fogging is an issue you may have to shot with shorter exposures and accept some depth of field loss or extra noise from a higher ISO.