A Guide to Startrails
One of my favorite things about photography is it allows us to see things we would never be able to with other media. To actually see the movement of stars over the course of hours is really incredible. If done right, startrail shots will be some of the most beautiful images you will ever capture.
The thing about startrails is you’ll never know exactly how the image is going to come out until you’ve finished editing the shot at home, long after the actual exposures were captured. It takes a real leap of faith to devote so much time and effort towards creating an image without knowing if it will be usable.
But startrails can be incredibly rewarding – of all the images I’ve captured over all the years I’ve been shooting, one of my favorites is a shot of startrails over a get in Terelj National Park, Mongolia. It took a lot of time to learn how to create the image, a lot of effort to set up the camera equipment, and a lot of patience and work to finally reach the end result. I’d like to simplify that process for you. Let’s get right to it.
Required Startrails Equipment:
Wide angle lens
Remote shutter release
A half decent sense of direction to find the north star (or a compass / smartphone)
Fresh camera battery or a battery grip with two batteries – this stuff is energy intensive
For you – warm clothes and a flask 🙂
Turn long exposure noise reduction OFF. Shoot jpeg to save memory space and time in post processing. Auto white balance is okay but if there are a lot of tungsten city lights you may want to consider setting it manually.
Compose the shot
Just like any other picture, frame and compose the shot. Use your compass, your smartphone, or your own ingenuity to determine the location of the North Star. It’s not always necessary to include the north star in the image, but be aware that the final results will vary drastically depending on how you compose your startrails.
Focus on the subject:
The light will be low and the camera will have a hard time autofocusing. Use your flashlight to illuminate your main point of interest and allow the camera to autofocus. Be sure your focus point is far enough away such that the stars will also be in focus. You are basically focusing on infinity. Once the camera has obtained focus, switch into manual such that the focus won’t accidentally wander later on. Be careful not to nudge the lens focus ring as you continue to set up the shot. If autofocus proves impossible due to low light, manual focus will be necessary. Use the LCD screen to verify focus in your test shots (next).
Throw your camera into very high ISO. Take a few short exposure test shots to get a feel for what kind of exposure will allow you to best see the stars. Don’t worry too much about the foreground just yet, but make sure your point of interest is in focus by zooming in on the LCD screen. This is your chance to lock in your settings – white balance, aperture, shutter speed, etc. The above test shot was at 12800 ISO, 3.2sec, f4.0. Foreground was “painted with light” (read on).
Expose for the foreground:
Set your camera to an adequate exposure value and take your high quality (low ISO) shot of the foreground. Camera meters weren’t designed to work in such low light conditions – you can use the in-camera metering as a rough starting point but don’t rely on it. Often times significant overexposing is necessary over the camera’s guesstimate. Some trial and error may be required; use the histogram to ensure your exposure is correct. If the foreground is VERY dark, you’ll have to “paint it with light” (fancy talk for “point your flashlight at the damn thing”).
For my Mongolia startrails picture, I overexposed by nearly 3 stops over what the in-camera meter suggested. Oh, and don’t worry about how the sky looks – at this point just get the foreground looking good. The above shot was 500 ISO, 24 sec, f4.0. Discerning eyes will be able to see the difference in quality over the test shot, even in this small web-sized version.
Setup for your startrails
Based on your test shots, setup your camera for the high quality (low iso) star trails. Remember that long exposure noise reduction is OFF (this is absolutely essential) so you’ll want a short enough exposure such that sensor noise is minimized, yet a long enough exposure such that the movement of the stars can be captured with minimal interruption. I’ve had success with exposures around 25-30 sec at 500 ISO. Take a few test shots first – play around with your aperture setting and make sure you can see the stars on the LCD after your exposures. Don’t worry if the image is dark or poorly exposed. As long as you can see stars, you’ll be okay. As you test the exposures, take note of what settings work.
Photograph Your Startrails!
Throw your camera into Bulb mode and connect your remote shutter if you haven’t already. Set your aperture and ISO values in the camera. Set your shutter speed and interval in the remote shutter. Interval is the time between shots. On my release, the minimum value is 1 second. I’d prefer a shorter time, 1/2 sec perhaps, but 1 second is adequate. I wouldn’t recommend any more than that because you’ll see gaps in the startrails. Set the number of shots to infinity and let it rip. Wait 2-4+ hrs, depending on how much rotation you want in your final image. For this image I actually went back into the Ger and slept till sunup (I do like my sleep). Of course, you won’t have ANY images if somebody grabs your camera while you’re sleeping…
Capture some blue in the sky
I prefer my startrails shots with some blue in the sky. The ONLY way to do this is to capture the startrails beginning at dusk after the sun sets, or to finish shooting at dawn before the sun rises. You’ll see a nice, deep, dark blue in the final shot. But make sure it’s just a hint of blue – capture too much light in the sky and your stars will be washed out by the bright sky (just like in real life)! Note that in the above image, you can still see the stars clearly.
Capture some dark frames
If you are shooting at the shutter speed/ISO settings recommended by this guide, this step is not necessary (but you can do it anyways if you like). At the end of your shooting, put the lens cap on and let your camera shoot 2 or 3 additional exposures at the same setting. With the cap on, your camera is essentially taking a picture of it’s own sensor. This will allow any sensor noise to show up, and you can later subtract this noise from the final image in post processing. This is called dark frame subtraction – it’s the same thing as long exposure noise reduction, except that you can do it manually instead of in-camera. I did not use dark frame subtraction in the Mongolia image.
At 25-30 sec a shot for 2-4+hrs, you’ll have somewhere in the range of 250-500 shots to process. This is why you shot in jpeg, remember 😉 Load up your star shots and foreground shot in Startrails.exe, a totally free program. Let startrails.exe do it’s thing, then edit the final image as you normally would. Consider using layers and masks to fine tune the look of foreground against the stars. You can also blur the stars with a gaussian/radial blur to add an extra feel of motion to the sky (I did). With any luck, your startrails will come out looking great.
But wait, there’s more
Stacking vs Long Exposure:
The technique suggested by this guide is called stacking, in that you create multiple images then add (stack) them together. Stacking is beneficial for many reasons. For one, if you have a problem with one shot (somebody walks in front of your camera with a flashlight) your final image won’t be ruined. The worst case scenario is you lose 30 sec out of a 2-4hr exposure… not too big a deal, and easily compensated for in post processing. The above image was an actual shot in my final startrails image – somebody opened the ger door as the camera was exposing. I blacked out the door light in photoshop and used the stars as part of the image. This would not have been possible with a single exposure.
The other benefit to stacking is you can more easily balance a bright foreground (like a city skyline) against the dark sky. Creating 400 twenty five second exposures of a city skyline won’t increase the brightness. Creating one 3hr exposure of a city skyline will washout everything else in your image, especially the relatively dim stars.
The argument for a single long exposure (as opposed to stacking) is that you don’t get gaps in your startrails. Gaps are a result of the short delay between shots inherent to using the remote shutter release. However by using radial and gaussian blurs you can minimize or hide the gaps entirely, and the overall image is likely to be superior.Keep in mind that a single long exposure will almost certainly require the use of Long Exposure Noise Reduction. This doubles your exposure time so if you’re shooting 2hrs worth of startrails be prepared to sit for 4hrs.
Cold weather shooting:
Cold weather: it’s great for your sensor, bad for you, and bad for your batteries. The colder the temperature, the less noise a digital sensor will gather at a given ISO. So feel free to jack up that ISO if need be. I personally recommend 500-800 ISO. Just remember a couple things: You’ll be cold – wear warm clothes. Your batteries won’t last as long – make sure they’re charged up and ready to go. After you’re done shooting, your cold soaked camera will gather condensation when brought back into a warm environment – turn the power off and put your camera in a plastic ziplock bag before you take it back inside.
Most of all, have fun and enjoy!
Airplanes and Stars over Chicago, IL. May 2012. Canon 5D Mark III, 260 x 25sec exposures @ 500 ISO, f9.0. Canon 17-40 f4L lens. Reverse graduated ND filter used to dim city lights. Image created using stacking technique described above.
Do you have more tips on creating beautiful startrail images? Share them below!