We discussed photographing star trails last month. That particular technique meant keeping the camera shutter open on B (Bulb) for a very long period, so that stars would register as lines of light. The problem with the technique is that a very long exposure gives issues with light pollution, stuck pixels and noise.
This technique means just shooting at relatively short exposures but shooting lots of them and then using software, effectively, to join up the dots, ie the stars.
The software I used is freeware and downloadable from www.startrails.de
and is Windows only. A very short tutorial on this software is featured at the bottom of this page. It is possible to do make a composite manually, using Layer Blend modes (Lighten) but it is obviously time-consuming. The Startrails software took about an hour to process my shots.
The final shot here is made up of 360 individual exposures each lasting 30 seconds with a four second gap between each one. You can appreciate that this took over three hours, so the first thing is to find a spot where you are prepared to babysit the camera so it does not get nicked, or use your garden. This is what I did.
|On the left, a single 30 second exposure. On the right, 360 exposures merged into one, thanks to Star trails freeware.
A tripod is essential, so too is a torch to help you set up. The other essential is a remote release
. You can do each exposure manually with a remote release allowing a few seconds between each shot but realistically given the cool evenings this might not be practical or comfortable. You would have to be very dedicated too.
So you need an interval timer or intervalometer. I have just bought a Nikon MC 36 multi function remote
that enables interval shooting. My Nikon D700
has an intervalometer built-in so I could have done it without the MC 36, but I had other reasons to buy the remote.
You will need a clear, moonless night – there was a moon due the nights I did my shots, but I checked moonrise/set times (www.timeanddate.com
) and knew it would not be a problem.
Over the past ten days, I have had four goes – two nights were failures because high clouds drifted over and messed things up. But on two nights, I had success.
You also want a night that is not going to be frosty because over three hours ice will form on the lens. This is less of an issue now but worth bearing in mind if you try this technique later in the year.
If your house has security lights, turn them off.
It also helps if you have an idea of where you are going to shoot from. In my garden, I set the tripod and camera up when it was still light and brought the camera back indoors until it got dark, but left the tripod still set up in position.
You need a fully charged battery, so this give me time to top up the charge in readiness.
I had done some homework first and I knew roughly where the pole star or Polaris would be in the night sky. I also knew that a 14-24mm lens
was not wide enough to include my house as well as Polaris. The importance of Polaris is that stars in the northern hemisphere appear to rotate around it, and it is easily found. Find the constellation of the Plough (or the Big Dipper) and follow the two end stars to Polaris. Google finding Polaris for more info or go to www.synapses.co.uk/astro/bearings.html
. At the moment the Plough is almost directly overhead.
When it was dark – an hour or two after twilight is fine – I fixed the camera onto the tripod, screwed everything down but before I set the intervalometer going, I did a couple of tests.
I winged it and guessed the exposure at 30secs at f/4 using ISO 400. That seemed fine. It did pick up light pollution of nearby Peterborough but the stars recorded as tiny pinpoints of light, which is all you need. Do your own tests for your chosen location. This was also long enough to record the interior lights of the house. I wanted them to add some atmosphere.
To be fair, this is not a technique that suits city dwellers because the light pollution will drown out the light from the stars anyway. I am a few miles out of the city.
A powerful torch shone on the subject will help you focus – manually, do not use autofocus - on the foreground. If you want to focus on the stars, don't assume that the infinity setting will focus on infinity. Just focus on something terrestrial but is some distance from you so the stars will also be sharp.
Do not bother with long exposure noise reduction. It is not practical to use and the benefits minor.
You have done your exposure test, focused up and now you are ready to shoot your run of long exposures. Just push the button and let the intervalometer do its thing.
In my case, I popped back inside and went back to the television and checked up on the camera during the odd ad break to make sure it was still working – I had to do this without the torch because it would have registered on the image.
Much, much later I came out and retrieved the camera and started work on the images – it was a very long night.
Startrails software is easy to use.
Open up the software, select the pictures you want to use and off it goes. As you can see here, the trails build slowly as each exposure is merged. The software has refinements like you can use a dark frame to help identify noise but I have not had the chance to explore the software fully yet.
Once the image was merged, I opened it in Photoshop. I used Hue/Saturation to get rid of some of the light pollution and I did clone out a light in the downstairs loo because it was too bright.
Close inspection also revealed that sharpness was not brilliant but easily good enough to allow me to make an A3 print.
You've read the article, now go take some fantastic images. You can then upload the pictures, plus any advice and suggestions you have into the dedicated Photo Month forum for everyone at ePHOTOzine to enjoy.