Star trail images can make a welcome break from shooting deep space, lunar or planetary. They don’t require a lot of equipment and you don’t have the inherent headache of a lot of technical stuff to get right. In fact, you can shoot good star trail images with an absolute minimum of gear. Pretty much all you need is a DSLR capable of bulb mode, a kit lens, a static tripod, and an intervalometer, or at worst a remote shutter release. You can also do these at the same time as shooting deep space objects if you have a spare DSLR that isn’t tied up imaging other stuff.
It’s often best to still have decent dark skies, but you can capture some pretty impressive images in your back garden in the city.
Composition
Although star trails on their own can look pretty awesome, I find it’s best to have some sort of foreground. This can be almost anything you want – a tree, a rock formation, even your car (if it’s interesting enough!). As I’m writing this I have my stock Canon 60D sat outside propped up on top of the kids guinea pig hutch shooting away, and it’ll do this until the battery goes flat. The foreground for this image is a tree to the left of centre, and a row of houses down the right side.
It helps too if the weather is crystal clear, although you can get some interesting effects with the odd passing cloud. Low humidity helps as well as the last thing you want is the lens fogging up halfway through. And make sure that there is either no moon, or if it’s out that it’s minimal and in the opposite direction to the one you’re shooting, ie behind you. Like all things astro, unless we’re shooting the moon itself, we don’t like it much!
Settings
I’ve found that 1 minute exposures are good for me using an 18-55mm f/3.5-f/5.6 kit lens, at ISO 100. I don’t like a lot of noise in my images so this works for me in light polluted skies of class 5. Make sure you turn off in-camera noise reduction as well as this will introduce breaks between the images and you’ll end up with concentric dots instead of solid lines.
Too low an ISO or exposure length and you won’t get a great deal. Perhaps the brightest few stars if you’re lucky enough. Too high an ISO and you bring more noise into the images. The same if you shoot exposures that are too long. In fact, go too long and the light pollution will likely overwhelm the images and you’ll be left with not much more than a blown out set of images that were a waste of time shooting. As with anything astro-related it’s a bit of a trade-off.
Ideally you want to shoot wide open as well, to get as much light as possible onto the sensor. Wide open shots also help with the framing. And use manual focus! It’s a waste of time letting auto focus even try. Stars aren’t that bright and with the best will in the world, AF just isn’t going to cut it. It’s also pretty pointless stopping down as you’ll lose some of that essential starlight if you do.
The above image was taken at ISO 800 using a stock Nikon D5300 and is a stack of ninety 30 second exposures. I’ve managed to keep a lot of the star colour and although there’s some light pollution, it’s not too bad, and in fact I feel it adds something to the overall image.
The great thing as well about shooting star trails is that you don’t need to worry about taking the calibration frames that you do with DSO work. Just think, no darks, no flats, no dark flats, no bias frames.
Of course, you don’t necessarily HAVE to centre on Polaris either. We just do that because we’re quite fond of that “wormhole effect” it produces.
The above image was taken looking in a more north westerly direction, using the same settings as the previous shot.
Post Processing
This is down to personal taste as much as anything else. To stack the images I use a free tool called Star Stax. This is a great, and fast, free resource that comes with a handy little thing called “gap filling.”
Generally I’ll load all the frames as RAW files into Adobe Lightroom, where I’ll make any edits necessary. Usually this will only be pretty basic stuff such as highlights, clarity, some dehaze, a bit of sharpening and noise reduction, as well as vibrance and saturation adjustments to enhance the colours in the stars. You only need to do this to one image. After you’ve made your edits, go to Loupe view and copy the settings to the rest of the images you’ve taken.
From there, export all of the images as JPG’s (I usually do this into a different folder) as Star Stax doesn’t like RAW files. This part will take some time, especially if you have a lot of images, which you should have, so go and make a coffee.
Once this is done, quit out of Lightroom and load the JPG’s into Star Stax. You have a number of options to go with at this point, but I tend to keep it pretty basic and keep settings etc to their default, only really making sure that “gap filling” is selected. Then sit back and watch it do it’s magic!
Once that’s done, and it generally only takes a few minutes, make sure you save the finished file before quitting out and returning to Lightroom where you can import the stacked image and do the editing to your taste.
Why Not Make a Video?
Using the JPG images, you can also use your favourite video editing software to make a pretty cool time lapse video of the movement of the stars across the night sky. Just make sure the images are in sequential order on the timeline and render. Et voilà!
Hope this was useful to some. As always please feel free to leave constructive feedback and comments. For now, clear skies!
AstroHeart UK Photography 