One of the topics I did not have time to discuss during last week’s presentation on photographing the Milky Way was making images of star trails. Ian Johnson has published some good tips and techniques for star trail photography over at Digital-Photography-School.com . It’s well worth a read if you are interested in this type of photography. Johnson discusses the basics of star trails, as well as composition, processing, light painting, and the effects of focal length and exposure times. It’s clear that this is an approach that is ripe for lots of experimentation and creativity.
I’ve learned one trick that works well for star trails if you don’t have an intervalometer, or like me, you are too lazy to use the one built into your camera. You do still need a cable release, though. Once you have your camera set up to capture the scene you want, set the camera’s shutter speed to the longest possible, without going into bulb mode. On my Nikon, this is 30 sec. Then, set the camera for high-speed continuous shooting. This is the mode that allows you to press the shutter button down and take photo after photo until you let up. Start the star trail sequence by locking the cable release to “on”. In this mode, the camera will take a 30 sec exposure, then another, and repeat until you unlock the cable release. The camera will fire away, shot after shot, until you stop it (or the battery dies). Using a wide angle lens, you probably want to let it go at least half an hour, and longer is often better. With a 50 mm or longer lens, a shorter time will give you good trails. Johnson walks you through the steps for combining the photos as layers, using the “lighten” blend mode in Adobe Photoshop. This will work in any software that uses layers and has the proper blend mode. I use a dedicated app called StarStax, which has several features such as gap filling (for the brief time between sequential images) and the ability to save out intermediate steps to create a time-lapse movie effect. StarStaX is free, but if you like it, the software’s author would appreciate some money for beer or coffee as a donation.
Another consideration is that you can control the apparent density of trails using the ISO setting on your camera. ISO 1000, for example, will give you many trails close together. ISO’s of 200 to 400 would give you fewer trails, mostly from the brighter stars. It’s another way to control the look of your image.
As with all nightscapes, knowing a little about the stars, planning for a foreground, and using some creativity will help you make great images.