Photographing Milky Way - A Tutorial


You probably have seen some awe-inspiring Milky Way pictures on the Internet or local stores, and wonder if you could take such majestic images using your own gears. In this article, I'm going to share some of my experiences of how to consistently shoot milky way photos. In fact, milky ways are relatively easy and predictable to photograph, as long as you take into consideration of these key factors: time, location, equipment/techniques. This article helps you to understand each of these factors. Using properly, I'm sure you will produce milky way photos as good as those you see over the Internet. If this article is too long to read, you can jump to the last section for example images and instructions of how these were made.



Time

The Milky Way consists of a bar-shaped galactic core region surrounded by a disk of gas and stars. It looks best in photos when the galactic core becomes visible in the sky. However, depending on the time of the year, the core isn't always visible. In the northern hemisphere, the core is only visible from late February to early September. Not all months are equal in terms of the core visibility. Starting in late February, the core becomes visible just before sunrise throughout the daylight time. The core then becomes increasingly visible for a longer time each day, peaking in June and July, when the Milky Way is up in the sky for all night. After the peaking months, the core becomes less visible again. In August or early September, the best time to view the Milky Way shifts to right after sunset. There are many apps you can use to find the milky way even before it rises in the sky. The one we used most often is called SkySafari. It tell you exactly when and which direction the milky way will show up in the sky - an extremely useful feature when you do the planning during day time!

The core is not always visible every night even in the peak months because there is another key factor that can make it unlikely to see it - lunar phrases. When it's a full moon, the moonlight is too bright such that it "washes away" the stars in the sky. A moonless night or new moon will be best to shoot  photos. We use this website to check moon phases. In other lunar phases, you need to find a time when the milky way is up but the moon has set or has not risen yet.



Location

Apart from how scenic difference places can be, light pollution is important in determining whether a place is good to shoot the Milky Way. I still vividly remember my childhood time counting stars in the evenings sitting in my grandma's backyard. Unfortunately, these days are long gone because of light pollution from cities. A research shows that 80% of Americans cannot see milky way under the sky where they live! Like moonlight in full moon phase, light pollution from cities can severely wash away the stars in the sky. That's why you wouldn't see many stars in cities nowadays. Most wilderness locations, such as national parks or national forests, are excellent locations to avoid light pollution. When you're arrived at a dark location, it will probably take you a bit time to have your eyes adjusted to the dark so you can actually see it.

While picking a specific location, we always like to have an anchor object in the foreground to contrast with the starts, placing the sky into a perspective. 

Milky Way over Devil's Golf Course - Death Valley National Park

Equipment/Techniques

With the right time and right location, you need to have the right tools to capture the grand scenes! First of all, you should realize that camera sensors are much more sensitive than our naked eyes when capturing the dim lights from those remote stars. Combined with sufficient exposure time, your sensor can capture a lot more stars you can possibly see through human eyes. That's why you can't see the astounding array of stars like those on photos even at the right location and time. With just naked eyes, it's more like a faint band consisting of light dots stretching the sky - but even that is awe-inspiring.

Amount of Lights

Apparently, under the dark sky, you want to capture as much lights as possible from those remote astronomical objects. Two factors are in play here: aperture size and exposure time. Of course, the two settings are important in any photography scenarios, but for night photography, we want to maximize the lights that reach to the camera sensor. This means a lens with a larger aperture is always preferable than one with a smaller aperture, and you should set the exposure time as long as possible without creating visible star trails (discussed later). A lens featuring at least f/2.8 aperture is highly recommended. We mainly use two lens to shoot the Milky Way -  Rokinon 24mm F/1.4 Aspherical Wide Angle Lens for Canon and Canon EF 16–35mm f/2.8L III. Read this article to learn more about equipments we use. For exposure time, you need to consider the Earth's rotation around its axis as well. Because of this, any exposure time that is longer than 20 seconds will produce star trails (more on this later) when pictures are zoomed in or printed large formats. Therefore, there is always a balance a photographer need to strike when setting the exposure time - maximizing the light and minimizing star trails. One exception of this is to use a star tracker (discussed later).

Star Trail over Upper Yosemite Fall - Yosemite National Park

Sensor Light Sensitivity (ISO)

In a nutshell, ISO is the level of sensitivity your camera is to available light. The higher the ISO number, the more sensitive it is to the light, and vice versa. Although increased sensitivity can capture images in low-light scenarios, it comes with an expense - added noises. Different cameras offer varying high-ISO capabilities. In general, to avoid using a exposure time over 20 seconds, you may need to bump the ISO up to 1600, 2000 or even 2500 when shooting the stars, depending on how good your camera for under high ISO settings. In general, a full frame camera performs much better in this regard. Unfortunately, cameras costing less then $1000 usually don't come with good high ISO performance. But this doesn't mean you can't shoot a milky way photo with such cameras. It's really up to your needs. For example, if you don't need to print your photos using large formats, it will be fine to use a cheaper camera and high ISO.



Star Tracker

Star tracker is an astrophotography tool used to capture sharp night sky images by enabling longer exposure without creating star trails. The way it works is to mount the camera on a star tracker, which in turns mounts to a tripod, and point the tracker to the Polaris star so the shooting direction is in parallel to the Earth's axis. This is essential for capturing trail-free photos. Once it's set up, the tracker will rotate at the same speed of stars moving across the sky. It allows you to expose you image as long as you want with no annoying star trails. In addition to this, you will be able to use lower ISO settings to reduce noises. I have to admit that setting up a star tracker is a pain in the neck but once it's set up, results are extremely awarding. Another challenge with using a star tracker is that if your image has a foreground, it will be blurry because the foreground will not rotate like the stars and the star tracker itself. In such cases, I would take two images, one with the star tracker on and one off, and combine the two in post processing.

Analysis of Example Images


This Milky Way rising over the Bonsai Rock was taken in early September 2015 at Lake Tahoe. At that time of the year, the best time to see the core is right after the sun completely sets and the sky turns into dark. We used Rokinon 24mm F/1.4 and Canon 6D. The settings of the photo are f/2.0, ISO 2000, and 20 seconds exposure time.


This picture was taken in early Jun 2016 at the Joshua Tree National Park using the same lens and camera as the picture above. You probably have noticed that his picture is significantly sharper, less noisy with much more details in the galactic core and areas around it, compared to the earlier one. This is because the image was taken with a star tracker, with the settings being f/2.0, ISO 1000, and 184 seconds exposure time. It has approximately 3.5 stops more lights than the above image, allowing the camera to register much more details. More importantly, it doesn't produce any star trails!



Star trails are not necessarily always bad. Star trailing is a pretty popular technique to create images like the one above. There are two approaches to achieve this. The first one is to have a single shoot exposed for an extended period of time, e.g. one hour, whereas an alternative approach is to shoot a large number photos with each exposed for a minute or so and combine them int a single photo using software like StarStaX. The above image was taken in May 2017 at the Rocky Mountain National Park using the second approach. Star trailing could become a boring exercise when you do enough of them. The key is to find interesting foreground as an anchor of an image.

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