By Ron Coscorrosa. Left: Upper Yosemite Falls and Polaris. The falls were front lit by a full moon. Many landscape photographers concentrate their efforts during sunrise and sunset, the two so-called golden or magic hours, but there is a third magic "hour" that is often neglected: night! With digital photography it's now easier than ever to take high quality night photographs, and this is especially true of star shots, including star trails and (the relatively less common) still star shots, such as those of the Milky Way. While digital has made most aspects of night photography easier, it does present its own unique challenges, mostly in the form of noise. This tutorial will address that issue, explain how to take star shots in the field, and how to post process them when you get home. Keep in mind that many of the techniques described are applicable to night photography in general and not exclusive to star photography.
Right: 14 minutes, f/5.6, ISO 320 at 45mm. This shot was taken just before dawn allowing some colors to creep in. Go where there are stars The first requirement for star shots is probably obvious: you need to go somewhere where you can see the stars! In general, this means away from the city and its corresponding light pollution. Higher elevations are generally better as well. There should be minimal to no cloud cover (though clouds can add interest for general night photography). Bland skies with no clouds generally make for uninteresting sunset and sunrise photos, but they're perfect for stars. Start shooting when it's completely dark An hour after sunset is usually too soon. An hour before sunrise is usually too late. In general, you'll want to shoot between astronomical dusk and astronomical dawn, when the sky is at its darkest. It's also best to shoot when there is no visible moon. Of all the rules, this one is meant to be broken. It is possible to take star shots with the moon, as long as it is out of your frame and is front lighting your subject (the stars will just be more subtle) such as the Yosemite Falls shot above. It's also OK to take shots as twilight transitions to night and night transitions into twilight (in fact, this can be a great way to get a little color in the sky, such as the shot in this section taken just before dawn). Buy a remote timer or remote switch For still star shots, where the exposure time is under 30 seconds (the typical maximum exposure time allowed in camera), you can get away without either of these, but they will make your life much easier. Prefer a remote timer over a remote switch, even though they're more expensive, as it will allow you to specify the exposure time and shoot continuously which is very handy for star trail shots. Carry an extra (charged!) battery The combination of long exposures and typically cold temperatures necessary for star trails shots drain batteries quickly. If you plan on combining your night photography with a sunset or sunrise (or both!) having an extra battery around is essential. Bring a flashlight or headlamp This will make it easier to see your camera, adjust the focus and other settings, and even better, find your way back to the trail head. Keep your camera warm If you are shooting exposures over 10 minutes at night, your camera may become colder than the air around it, causing the relatively warmer air to condense on the colder camera, so it's important to at least try to keep the camera warm. How? One technique that seemed to work was rubber banding hand warmers to the lens and wrapping the camera in a towel. Another possibility would be a battery powered hair dryer that you fire at regular intervals. Astronomers face the same problems with telescopes and they have specialized equipment for dealing with it, though some of it is quite pricey. Use manual focus and manual/bulb exposure modes When it's dark, auto-focus doesn't work, so use manual focus. Exposure meters are also often incorrect at night (sometimes varying wildly from shot to shot) so you should use manual exposure mode (for still shots or test shots), and bulb exposure mode for shots over thirty seconds. When shooting in bulb exposure mode, be sure to disable mirror lockup. Use the histogram, not the LCD When your eyes adjust to the darkness, images on the LCD may appear brighter than they actually are, the histogram is a more reliable representation of the exposure. Remember, star photos are landscape photos too! This means that you still need to be concerned with composition, subject, and sharpness. Unless you have a bright moon, it's very difficult to see at night, so it helps if you're familiar with the area and already have a composition in mind.
Left: 23 seconds, f/2.8, ISO 3200 at 18mm. Trees often make good foreground subjects. Composition and Focus Now that those requirements are met, you're ready for some star photography! First I'll explain how to take still star shots, and then later how to take star trails shots. You're obviously not limited to these two extremes (there is a lot of room for experimentation between 20 seconds and two hours), but once you know how to do both, you can do any type of star shot. For moving and still star shots, and night shots in general, you need to make sure your composition and focus are both correct. It's hard enough to see with your eyes when it's dark out, and nearly impossible to see through the viewfinder. Fortunately, since you're shooting digital, you can cheat. Take some sample shots (at a really high ISO and wide open to save time) and verify that your composition looks correct on the LCD. Make sure that the stars are prominent in your composition and complement your other subjects. Now that you have your composition, you need to ensure that your primary subject is in focus (as most night photos are shot with a large aperture it's critically important to get your focus correct as you have little depth of field). Make sure you're in manual focus, and start just shy of the infinity marker, and take another sample shot at a high ISO, and then zoom in on it on the LCD and verify it's sharp. You should then take a sample shot with the focus marker a few millimeters to the left and another a few to the right, just to be certain you have the optimum focus. It can often take me 6 shots before I'm sure I have the correct focus. Try doing that with film!
Right: 25 seconds, f/2.8, ISO 3200 at 16mm. If you get lucky, you may capture a shooting star, this photo has two. Minimizing star movement Most people associate star shots with star trails, but with digital, it's now possible to take good quality shots of still stars too. When shooting still star shots, the most important consideration is to minimize star movement. Minimizing the star movement requires four things: 1) Keep the exposure time down. 30 seconds is pushing it, I generally aim for 25 seconds or less. 2) Shoot at a wide angle (16-35mm on a full frame camera). If you shoot at a longer focal length, you will magnify star movement. 3) Shoot at a high ISO, this will allow you to capture more light in a shorter amount of time. You will generally want to shoot at least ISO 3200 and possibly higher. 4) Shoot at a wide open aperture (on most wide angle lenses this will be between f/2.8 and f/4). Again, this will allow you to capture more light in a shorter period of time. If you can meet the 20-25 second requirement at a lower ISO, then you definitely should. Now that you know how to minimize star movement, take a few sample shots and verify that the exposure looks good on the the histogram. If it's too dark, you'll probably need to increase the ISO. Remember, memory cards are cheap, you should experiment with different ISO and exposure lengths while you're out in the field. To minimize noise, you should err on the side of over exposure, if you try and take an underexposed (and already noisy) image and brighten it in post production, the noise will become even worse than it already is. If you're feeling adventurous, you can light paint your foreground element if it is close by (using a headlamp, flash light, or whatever else you have at your disposal).
Left: 20 seconds, f/2.8, ISO 4000 at 29mm. A heavy dose of noise reduction was applied for the stars, which also caused a corresponding loss of foreground detail. Noise Reduction So now that you have a few properly exposed, composed, and sharp photos of the stars, you must be done, right? Unless you like a lot of noise in your photos, then there's still some more work to do. I've found that liberal application of good noise reduction algorithms (such as Noise Ninja, or the Luminance Noise Reduction in Lightroom 3, unfortunately the built in noise reduction in Photoshop is notoriously awful) can all work quite well on stars which usually don't have a lot of detail or color.
Right: 6.3 minutes, f/2.8, ISO 500 at 29mm. The purpose of this shot was to get a low noise version of the foreground mountain. Shoot a better foreground If your foreground is a silhouette (such as a tree), then after applying noise reduction somewhere in your normal post-processing workflow, you should be done. However if you need to preserve detail in your foreground (such as for a mountain), then you probably just got rid of all detail when you did the noise reduction (d'oh!). At this point, you have three options: 1) Live with the loss of detail 2) Apply the noise reduction only to the stars 3) Take another exposure in the field at a lower ISO and longer shutter speed, and use that as your foreground blended with the star shot. The best results are with the third method, which I'll describe. The second method is similar, but instead of using a new exposure you re-use the original one before you applied the noise reduction. While still out in the field, and obviously without changing your composition or focus, take a longer shot at a lower ISO (for best noise performance, keep the exposure less than 6 minutes). This shot will now be used for your low-noise high-detail foreground.
Left: The final shot, a blend of the stars on the first and the foreground mountain of the second. I also cloned out the climber head lamps and did some curves and saturation adjustments. Better Together So now you have two exposures that you need to combine together, using layers and masks in Photoshop: 1) A short exposure at high ISO with heavy noise reduction used for the still stars 2) A long exposure at a lower ISO with less noise and more detail in the foreground Open the two shots as separate layers within a single Photoshop document, with the shot of the stars as the top layer and the shot of the foreground the bottom layer. You then want to add a layer mask on the top layer. Your goal is to mask out the foreground by selecting it and painting the layer mask black, this will allow the high-detail version of the foreground to show through. There are several ways to do this (selections and masks are a complicated topic worthy of their own tutorial), for this example I used the magnetic lasso tool and then zoomed in and fine tuned the selection afterward with the normal lasso tool.
Right: 5 minutes, f/2.8, ISO 500 at 18mm. A sample exposure of the 25 exposures used for the final star trails shot. You can see the big dipper on the upper left of the mountain, and the fixed position of Polaris 1/3rd from the right near the top. Star Trails There are two ways to take star trails shots: a single long exposure, or multiple shorter exposures blended together. For digital photography, blending shorter exposures together is preferable. Why? 1) Less noise. Any exposure over five or six minutes, even at a relatively low ISO, will have a lot of noise on a digital camera. By limiting your exposure time you likewise limit the noise. 2) Risk mitigation. What happens if you run out of battery one hour into shooting? Or if your lens fogs up after thirty minutes? Or an airplane flies through your exposure ten minutes into it? By taking multiple shorter exposures you can still end up with a usable result. For your composition, most long star trails shots look better with Polaris (the north star) in the frame, other stars will form concentric circles around Polaris. Polaris is almost true north (not magnetic north), it forms the end (handle) of the little dipper, also the last two stars in the big dipper point to it (you can use this picture for reference). You'll want some buffer around Polaris to show the stars moving on all sides. As with still star shots, you'll want to take a few sample exposures at a high ISO (to save time) to verify composition and focus. I like to shoot each individual exposure from 4 to 6 minutes, no higher than ISO 500, at an appropriate aperture (if it's really dark, that might be wide open, if the shot is front lit by the moon, you can shoot at a smaller aperture or lower ISO). As long as you keep the exposure under 6 minutes the noise shouldn't be too bad.
Left: The final blended exposure, approximately 2 hours of shots. Blending multiple exposures Next you want to take a 4-6 minute test shot, to verify your exposure and to verify the star movement around Polaris looks correct. Then set your timer to fire continuously (on my timer this is shown as "--") with 4-6 minutes for each exposure and with no delays between exposures (any delay between exposures would show up as gaps in the star trails). After that, set an alarm for on your watch or cell phone so you know when to stop. Note that you could set your remote timer to stop after a set number of exposures, but I prefer to let it fire continuously, that way if an airplane flies in, or something else gets in the way, all I have to do is reset my alarm and not mess with the camera or timer again. How long of a duration should you capture? That's up to you, but for shots with Polaris in them I aim for 90 minutes to two hours. If you want, you could take a longer brighter exposure for the foreground so that you can possibly blend them in later using the same technique described above for still star shots. Now you have a bunch of 5 minute exposures sitting around, what do you do with them? Open each of them as a layer within a single Photoshop document, and set the layer blending mode to lighten (this will take the brightest area of each shot, which is typically the stars). If you zoom in at 100%, you might notice some small gaps between the stars, if that's the case, you can use the screen/lighten blending combination as described in Floris van Breugel's excellent star trails tutorial which will eliminate those gaps. The resulting image will have noise in it, but not nearly as much as the still star shots. A normal application of noise reduction should do the trick. Two hours is a long time to devote to a single shot, so you'll want to make sure you're comfortable, and you'll also want to make sure you don't bump the tripod!
Right: 6 minutes, f/5.0, ISO 400 at 28mm. If you can't beat light pollution, join it. This is a shot of Mt. Baker facing west to the town of Bellingham. Many photographers pack up their gear after sunset, but with digital, taking night photographs has never been easier, it's now possible to get the exposure, focus, and composition correct even when you can't see what you're photographing! Noise is still a concern, but as digital camera sensors improve, it will become less and less of an issue. Huge improvements have been made in the last few years and I'm optimistic that in the future it will actually cease to be an issue altogether. After a few outings at night you'll soon realize that sunset through sunrise is one large photo opportunity. Unlike during the middle of the day, night time light, even with a full moon, is much more diffused and soft, and unlike sunset or sunrise, night time light is a lot more predictable. If the conditions are right, you can end up with stellar shots. Yeah, I went there. Discuss this on Digital Grin Forums.