By Peter Zelinka
The Milky Way “season” is generally considered to run from April through October. By that we mean that the galactic core, or center, of the Milky Way galaxy is visible in the Northern Hemisphere and astrophotographers have the best chances of capturing, well, stellar images. But there’s a lot more to successful Milky Way photography than that. This article excerpts some tips from a NANPA webinar I did a while back. The complete webinar is available in the Members’ Area of the NANPA website.
Where and when
The Milky Way rises in the southeast sky early in the morning during Spring. I’d recommend waking up at 2 or 3am and driving to a nearby dark sky to enjoy the view! In the fall, the Milky Way will already be high in the southwestern sky by dusk. If you want to get a Milky Way shot, you’ll need to be on location at sunset. The sweet spot for Milky Way photography, however, is during the summer. The Milky Way core will be shining bright in the southern sky all night long. For those living at high latitudes (50◦+) you may want to try heading south for a trip. The further south you travel, the higher up in the sky the Milky Way core will be. Once you reach the equator, the entire Milky Way will span overhead.
When planning a night of Milky Way photography, you’ll want the darkest sky possible. You’ll have to take the position and phase of the moon into account and look for a date when there is a new moon or the moon is below the horizon during the time you’ll be shooting. I use the website TimeandDate for a quick overview of the upcoming moon cycle. Of course, moonlight isn’t the only problem we have to worry about.
By far the biggest challenge with astrophotography is finding a dark sky, away from city lights. I use Lightpollutionmap.info, which shows a nice overlay of light pollution across the world. Ideally, you can travel to a Black or Blue zone on the map for really dark skies. However, even if you can only get a Yellow region, that would be fine. You should still be able to see the Milky Way with your naked eye in a Yellow area.
The only thing left for your planning is the weather forecast. In addition to weather reports and your favorite weather app, I use Clear Dark Sky. It was created for telescope users but gives us a lot of valuable intel. The website can be a little confusing at first, but just remember – you want to see as many dark blue squares as possible. That indicates that you’ll have good conditions – calm wind, minimal humidity, no clouds, good “seeing”, etc…
I prefer a full-frame DSLR or mirrorless camera. You can certainly use a crop sensor or micro 4/3 camera, but full-frame sensors have several advantages (more on that later). You’ll also want a fast, wide-angle lens, something like a 24mm or wider lens with an aperture of f/2.8 or larger. It’s dark out and the light from stars is faint, so the more light that reaches your sensor, the better your photo. A tripod is a necessity because of the long shutter speeds you’ll be using. A remote trigger will be helpful for the same reason.
I highly recommend getting a headlamp with a red light function. A red light preserves your night vision. You can turn on your red headlamp, adjust your camera, and still maintain your night vision. That wouldn’t be possible with a regular white light. A white light could also mess up the photo of anyone else shooting near you, where a red light won’t be as obtrusive.
Make sure to bring backup batteries. I can’t tell you the number of times I have gone out and shot with other people, and they only have one or two batteries (both half dead) and we’re going to be out there shooting for hours. Make sure you have fully charged backup batteries! When I was on my road trip, I had a car charger. I could take my batteries, pop them in there, plug it in my cigarette lighter, and always have a battery charging as I’m headed to my next location. That’s really huge thing for me.
Focus: One of the most frequent questions I get about Milky Way photography is, “How do I focus at night?” A lot of people have trouble with that, but here’s the trick. First, I set my camera (and lens, if necessary) to manual focus and set my lens to infinity. Then I switch on Live View. I find the brightest star I see and zoom in on it (magnifying it in Live View, not zooming the lens). I move the lens focus ring back and forth very slowly until I think I have it as sharp as possible, step back, and double check. This process usually takes about 20 seconds. I keep turning the focus ring back and forth very slightly, until the stars are as small as possible. Then I know I’m set for the night. A very wide lens, like 14mm on a full-frame camera, has a large enough depth-of-field to also maintain reasonable sharpness in a foreground that’s a couple of feet or more away. In other words, if your stars are sharp, your foreground should be sharp too! Alternatively, you could turn on a flashlight very briefly to illuminate your foreground. Then use Live View to focus on the foreground.
If you’re still having trouble focusing at night, a Bahtinov Mask can really help! These are pretty simple, but effective filters. A Bahtinov Mask is usually just a piece of plastic with a specific pattern of slits in it. This pattern produces a diffraction spike on bright stars. With the Bahtinov Mask placed in front of your lens, you can aim up to a bright star like Polaris. Then, either use Live View or take test photos to check the diffraction spike. Generally, the diffraction spike should have 3 lines. Once the middle line is directly in the center, you know your lens is perfectly focused. A quick google search will demonstrate this diffraction spike pattern clearly, and clear up any confusion. In general, I only recommend a Bahtinov Mask when shooting 70mm+. They aren’t as effective when using a wide-angle lens unfortunately.
Finally, remember to turn off auto focus! There’s nothing worse than finally getting your focus perfect, only to have the camera automatically try to focus when you click the shutter button. All that hard work gone in an instant.
Aperture: The wider the better. If your lens only opens up to f/4 shoot at f/4. I’ve seen plenty of people take good Milky Way photos at f/4, but I highly recommend getting a lens that can open up to at least f/2.8. An f/4 lens transmits only half the amount of light of an f/2.8 lens, and you want to make sure you’re getting as much light into the camera as possible.
There is one important caveat here. A wider aperture isn’t always better. For example, I have a Sigma 35mm Art f/1.4 lens. f/1.4 lets in 4 times more light than f/2.8! That’s a big deal! Unfortunately, I don’t ever use my Sigma lens at f/1.4 due to Coma and Vignette. The Coma (star distortion) is so bad at f/1.4, that my stars look like birds flying through the sky (wings included!) This is especially prevalent with the cheap 50mm lenses from Canon/Nikon, etc… The only way to get reasonably sharp stars with the Sigma 35mm lens is to stop down to f/4. Now I have pinpoint sharp stars, but I’m capturing 8 times less light! This is always the tradeoff in astrophotography – do I want sharper stars or more light?
Shutter speed: The shutter speed is mainly dependent on the focal length of your lens. The wider the focal length, the longer you can shoot without star trails. Think of it this way, the stars are continuously moving overhead. If you had a big telescope and zoomed into the moon, you’d see it moving very slowly in real-time. However, if we stare up at the moon with our naked eye, we can’t see any discernible movement. The same principle applies to our lenses. You can usually shoot about 15-20 seconds with a 14mm lens before noticing any significant star trails. However, if you use a 100mm lens you will see star trails within 5 seconds!
The 500 rule: This was developed back in the film days as an easy way to calculate exposure in the field. Take 500 and divide it by the focal length of lens. This will give you the max shutter speed without star trails. For example, using a 15mm lens we get 500/15 = 33.3 seconds, where a 35mm lens give us 500/35 = 14.3 seconds. For me, these exposures still show considerable movement in the stars, which makes them look slightly elongated, so I don’t recommend using the 500 rule. Instead, use the 300 rule, so 300/15 = 20 seconds and 300/35 = 8.6 seconds. Like I mentioned in the Aperture section, do you want sharper stars or more light?
If you’re on a crop sensor by, there’s something else to keep in mind. Generally, you multiply a crop sensor lens by 1.5 (1.6 with Canon) to get a full-frame equivalent. So, an 18mm lens on a crop body is equivalent to a 24mm on a full frame (18 x 1.5 = 24). You need to include that same calculation in your “500” or “300” Rule. For the 500 rule, the calculation is 500/(18 x 1.5) or 500/24 = 20.8 seconds. To put this very simply, a crop sensor camera will see star trails faster than a full frame camera.
Since cameras don’t have options like 14.3 or 20.8 seconds, always round down to the nearest setting.
NPF Rule: Today’s digital sensors have a greater dynamic range and better resolution than film, so the old 500 rule doesn’t work as well. In addition to the 300 rule, I also use the NPF Rule, a calculation created for digital cameras that takes into account the sensor being used. There are several NPF calculators online and in apps like PhotoPills.
Histogram: As you’re shooting, you’ll want to look at the histogram on your camera. When you look at your image on the back of the camera at night, all your photos are going to look really bright and you’re going to think all your photos came out great, or maybe even look overexposed. (This is especially true if you don’t change the monitor brightness. I recommend reducing monitor brightness by -4 or -5 when photographing stars. Most cameras include that function in the menu. Check you user’s manual or Google it.) When you look at the histogram, it’s always going to tell you what’s actually going on, whether you’ve nailed the exposure or not.
ISO: Don’t get too worried about ISO, it’s not that important in the grand scheme of things. However, there are a lot of misconceptions about ISO, especially in regards to astrophotography. Here’s the way I think about ISO – I set my Aperture and Shutter Speed first, based on the criteria we discussed earlier. Let’s say f/4 and 20 seconds. Then I adjust my ISO based on the light pollution. If my image is too bright, I lower the ISO. If the image is too dark, I increase the ISO. It’s that easy.
Let’s say I’m out in the desert, with no major cities around for 100 miles. I can put my camera to f/2.8, 20 seconds, and ISO 6400. This should give me a nicely exposed image. If I still think the foreground is a bit too dark though, I could increase the ISO to 12,800.
On the other hand, maybe I’m back in Ohio shooting on farmland in the suburbs. If I use f/2.8, 20 seconds, and ISO 6400 my image will be very bright! There’s too much light pollution here, so I need to lower my ISO accordingly. I can try ISO 1600 and see if that looks better.
Regardless of your location, I’d recommend starting at ISO 6400. That’s the one I use most of the time. Experiment with different ISOs when you’re out there to see what works best for your specific camera and lens.
There’s one final point I want to make about ISO – it does not change your camera’s sensitivity to light. ISO simply “amplifies” or “brightens” whatever light you captured in your image. The only way to capture more light, and have a cleaner image, is to use a wider aperture or longer shutter speed. For example, if I take an image at f/2.8 and 20 seconds with ISO 100 the image will be very dark. If I increase the ISO to 6400 the image will be much brighter! However, the amount of light captured has not changed. We still captured 20 seconds of light at f/2.8. The light was amplified by the higher ISO after the data was captured.
Here’s a good test to try one night. Take a series of photos using the same Aperture and Shutter Speed, but increase the ISO by one Stop each time. So – take a photo at ISO 400, 800, 1600, 3200, and 6400. (Make sure the Aperture and Shutter Speed stay exactly the same throughout though). Now you can load all 5 photos into Lightroom or Camera RAW. Increase the “Exposure” slider by +1 for the ISO 400 image. Increase the “Exposure” slider by +2 for the ISO 800 image, etc… Now compare all the photos. They should all have the same brightness and look identical up close!
This leads us into ISO Invariance, which is enough to fill an entire article. The short version is that every camera performs differently at night. Nikon and Sony cameras generally have better sensors, with more dynamic range. Canon sensors tend to perform worse at night, especially if your ISO is too low (and you need to brighten your image in post-processing.) That’s why I recommend you try my test described in the paragraph above. You should learn how your camera sensor performs so you can make the best ISO choices.
White Balance: The white balance you choose is very important, as it will have a big impact on the mood of the photo. If you want to have accurate colors at night, use daylight white balance. This will create an oddly warm photo though, especially if you’re shooting in a light polluted area. In fact, most people will find that the natural sky colors aren’t very pleasant. The “real” colors of the sky are surprisingly orange, even in dark skies with no light pollution. However, almost every photo you’ve seen of the night sky has a nice blue/purple color cast. While these colors are atheistically more pleasing, they aren’t exactly “real”.
Astrophotography is an art, so feel free to use any White Balance you prefer! I generally set mine around 3700K. If you forget to set the White Balance in-camera, no big deal. You can always adjust the White Balance in post-processing without any quality loss, so long as you are shooting in RAW.
You will want to include a foreground in your Milky Way shots to anchor your composition. I always try to find something interesting to compliment the Milky Way overhead, whether that be a simple dirt road, massive sandstone arch, distant mountain, or lone tree.
When I was learning astrophotography in Ohio, we didn’t exactly have many interesting foregrounds. That meant I had to get creative. Some things that worked for me are – light painting, having someone standing in the foreground, steel wool spinning, even car taillights streaking through the foreground can make for an interesting composition. Now that I’m living in Utah I have a lot more options! There’s plenty of unique desert landscapes that nicely pair with the Milky Way.
A few bonus tips
Hot Pixels: The longer the exposure and higher the ISO, the more heat builds up on your sensor and that can lead to hot pixels. These show up as bright, colored spots all throughout your image. If you’re not careful, these can ruin an otherwise good photo. One way to deal with this in the field is to use Long Exposure Noise Reduction (LENR). This setting tells the camera to take two exposures. The first exposure is your normal photo, but the second exposure is a “dark frame”. This dark frame has the same settings but the mirror stays down, so no light reaches the sensor. You could always put your lens cap on, and cover the viewfinder to make sure no light enters the camera. The dark frame is used to map out all the hot pixels. Then, the camera automatically identifies the hot pixels in the dark frame, and subtracts them from the original exposure. From your point of view, a 20 second image with LENR turned on will take 40 seconds to complete. At the end, you’ll have a single image with no hot pixels!
I would only recommend using LENR on very hot nights (70F+), or if you are shooting 1+ minute long exposures. In both cases, you’re likely to see hot pixels. Turning on LENR is the fastest and easiest way to remove them.
Return your settings: This is one I’m still trying to make myself learn. Make sure you change everything back to your normal settings before you pack up and leave. There are few things more frustrating than going out the next day and seeing a bear by the roadside or a bald eagle flying overhead and, when you go to take your photo, your camera is set to f2.8, ISO 6400, 20 seconds LENR, and manual focus. You want to shoot wildlife but your camera is ready for Milky Way photography! By the time you reset everything, the moment is gone. Just remember to set everything back to your normal settings, because forgetting will invariably mess you up the next day.
I know I’ve thrown a lot at you in this article today! If there’s one point to remember, it’s this – the best way to get better astro images is to capture more light!! There’s two main ways to capture more light – a longer shutter speed and a wider aperture. Both have drawbacks, as we discussed today. If you want to overcome both problems, then I’d highly recommend looking into a Star Tracker. This simple device will move your camera along with the motion of the stars, allowing you to shoot 5+ minute exposures without star trails! You can now have the best of both worlds – a long shutter speed to capture a lot of light, and a smaller aperture (f/4) for sharper stars. Out of all the things I’ve learned about astrophotography in the past 7 years, the star tracker revelation has been the most important one.
Peter Zelinka is a nomadic nature photographer originally from Ohio. In 2016 he quit his full-time IT job to pursue a photography career. It wasn’t easy though, and he spent the next 4 years living out of his car, traveling around the country to capture the beauty of the West. In 2020 he finally settled down in Kanab Utah, a great place for astrophotography! Now he spends his days creating astrophotography tutorials, writing articles, and going on the occasional hike. You can follow his work on his website, YouTube, and Instagram.