Night Sky Photography - Aaron Priest Photography

Night Sky Photography

2012-07-11-67877

What Is Landscape Astrophotography?

There are many kinds of night sky photography: deep space objects with telescopes, wide field, moonlit and long exposure landscapes, timelapse and star trails, panoramas, and many others. This article is mostly about what a DSLR can capture on a tripod with a wide angle lens and proper exposure, combining landscapes with wide field astrophotography for a compelling image that has a strong composition with interesting foreground elements and a dramatic view of the sky—particularly the Milky Way.


Article Index


Terminology

There are some basic terms that should be defined to help you know which time of night is best to photograph different subjects, such as the Milky Way. Generally speaking, night is between sunset and sunrise, but of course it does not get suddenly darker like a light switch! There are some transition periods between day and night that are good to know. This transitional period is known as twilight, and can be dawn (morning) or dusk (evening). Most photographers are familiar with the phrases “golden hour” and “blue hour”. They are rather broad terms without any real scientific measurement, but they are the coveted times of day with beautiful light before, during, and after sunset or sunrise. We’ll try to define them a bit more accurately in a minute. But first, let’s look at the scientific terms.

Twilight is defined in three distinct phases, and is based on the elevation of the sun: civil, nautical, and astronomical. Sunset and sunrise are when the sun is at 0°elevation on the horizon. To see the sun at this measured time you would have be at sea level and observe the sun rising or setting over the ocean with no obstructions. If you are higher on a mountain, you will see sunrise earlier. If you are in a valley, you will see it later of course. For example: Cadillac Mountain in Acadia National Park throughout most of the year is the first place in the United States to see sunrise because of the elevation and how far east it is. Other times of the year it is Mars Hill in Aroostook County.

Twilight Phases

Civil twilight is when the sun is between 0°and -6° below the horizon. Nautical twilight is -6° to -12°, and astronomical twilight is -12° to -18°. Twilight at dusk or evening begins with civil twilight at sunset, dims through nautical twilight, and ends after astronomic twilight when the sun is -18° below the horizon. At this time the night sky is as dark as it will be for the rest of the night until dawn when the process will reverse with astronomic twilight beginning when the sun reaches -18° below the horizon, climbs through nautical twilight, and ends after civil twilight at sunrise. Blue hour and golden hour overlap some of these twilight phases and definitions of them vary, but you could consider golden hour to be when the sun is 6°above the horizon to -4° below the horizon, and blue hour from -4° to -6°. This website is a great resource to bookmark for more details.

The Milky Way is best photographed during the darkest period of night between the end of astronomical dusk and the beginning of astronomical dawn, particularly during a new moon in an area with no light pollution and during the seasons where the photogenic galactic core is still visible above the horizon. More on that subject later. The brightest stars and a few planets are prominent during the darkest period of blue hour and nautical twilight. This is my favorite time to either start a star trails timelapse, or end one, with some rich dark blue colors in the sky.

To translate these twilight terms into specific times for our geological location we have to use apps and almanacs. Two of my favorite mobile apps for this on both iOS and Android are PhotoPills and PlanIt! for Photographers. Both are powerful all-in-one programs that I’ve found no equal for and every photographer should own, but there are several other programs you can jump between to get some of the same information.

Weather Underground is good for looking up current weather and sky conditions, moon phase, and start/end of each twilight phase for your location, particularly in the astronomy section.

Stellarium is free for Windows, Mac, and Linux and a great tool for looking at constellations, planets, sun, moon, and Milky Way positions for a specific location and date.

Light Pollution

With the advent of electricity, increasingly brighter and more efficient lighting like LEDs, and people moving into densely-populated places like large cities, artificial light pollution has become a very real problem. A century ago almost anyone could look up and see billions of stars with the naked eye, but today there are millions of people who have never seen the Milky Way. There are organizations like the International Dark-Sky Association that are working to educate others and help preserve our night skies.

For photographers, this means we have to find an area away from artificial light pollution to photograph the night sky. In 2001, astronomer John E. Bortle created the Bortle Scale to measure the brightness of the night sky. It ranges from Class 1 to Class 9, with Classes 1 through 3 being ideal for Milky Way and night sky photography. https://www.lightpollutionmap.info is one of the best online maps to chart the Bortle Scale and light pollution around the world. There are a number of overlays you can choose from for data, including local SQM/SQC reports if any have been made by other users. You can measure your own location with Dark Sky Meter (iPhone only).

Two of my favorite mobile apps for light pollution are Dark Sky Finder and PlanIt! for Photographers 

Dark Sky page of PlanIt! for Photographers

Tide & Weather

If you are shooting around the ocean, this is a critical subject you must be aware of—potentially life-threatening and certainly hazardous to unattended camera equipment. It’s easy to lose track of time and get stranded at a place you easily walked out to at low tide, or leave a camera running for twenty minutes or more and find the tripod legs under a foot or more of water unexpectedly. Like weather or anything else, it is wise to plan ahead and be aware of circumstances, such as the times of high and low tide, and the amount of rise. Storms further out in the ocean can make it surge higher or faster than expected too, even if the weather is clear where you are.

Most GPS units will give you tide estimates for your location. One of my favorite iPhone apps is Tide Charts Near Meit only requires cell phone service once for an area so load it up when checking the weather before heading out in the field where you might not have service. Weather Underground has a great marine forecast section that includes current heights of waves based on marine buoys.

A few of my favorite websites and apps for weather and sky conditions are:
http://clearoutside.com Also has a really good mobile app. I've found this to be one of the best for cloud cover predictions.
https://www.ventusky.com Look at temp, precipitation, clouds, wind speed, snow cover, etc.
Storm Radar by the Weather Channel for general weather reports, Apple & Android versions.


Astronomical Events

Moon Phase

One important consideration for good Milky Way photography is the moon phase. It is best to shoot during a new moon, as the brightness of a quarter moon or more will wash out the Milky Way, and it is impossible to capture the Milky Way during the weeks the moon is sitting in the middle of the galactic core. This is easily predicted with software like PhotoPills and Stellarium though. Often the week before and after a new moon can still be useful for Milky Way photos as the moon rises or sets during the night and still leaves a few hours of shooting. Also, moon rises and moon sets are beautiful for timelapses, and a quarter moon or less behind you makes for some great foreground lighting. A quarter moon or more will give very strong foreground lighting and interesting shadows for timelapses. With the correct white balance it can look like a daytime photo, but still have several stars in the sky. The sky will be quite blue like nautical twilight, and timelapses or star trails can be very beautiful with fewer stars and brighter foregrounds.

It is very difficult to shoot a proper exposure of the moon and a landscape after golden hour and blue hour; the dynamic range is too great for current sensor technology, and even with HDR it is difficult to process and make it look natural. It’s usually better to have the moon at your back after nautical dusk. If shooting the moon with a telephoto lens and no landscape you’ll find the craters have more details around half moon when they are side lit from the sun with more contrast. The moon moves very fast though, so you’ll need a quick enough shutter speed at long focal lengths to get a sharp photo, preferably from a tripod to avoid camera shake. Xavier Jubier made a pretty nifty online Moon Exposure Calculator for calculating the brightness of the moon during different moon phases with suggested shutter speeds for specific camera sensors and focal lengths: http://xjubier.free.fr/en/site_pages/astronomy/MoonExposureCalculator.html

PhotoPills has a great article on shooting the full moon: https://www.photopills.com/articles/how-plan-next-full-moon

Handheld photo of a crescent moon taken on September 23, 2017, 18:57 in Lee, Maine with a Nikon D850, 200-500mm f/5.6, and TC20E-III 2x teleconverter at 1000mm, f/18, ISO 800, 1/60sec.

Aurora

Aurora Borealis (Northern Lights) and Aurora Australis (Southern Lights), like the Milky Way, are best seen during a new moon with little artificial light pollution, although I have seen them strong enough to photograph during a full moon (that is rare where I live). Both take place over the polar regions and the closer you get to the equator the less visible they are. The Northern Lights are more popular due to more geographical land masses to view them from, but the Southern Lights are no less intense or beautiful. Similar to the weather, they are not predictable very far out in the future (a week at most really, and only accurately to a few hours). This is mostly because the intensity of the lights are heavily dependent on Earth’s magnetic field, which fluctuates unpredictably. There are three measurements used for aurora reporting: Kp, G-scale, and Bz. Kp is an index from 0 to 9 and measures the intensity or strength of the aurora and how far the oval reaches on the globe, with higher numbers being further distances from the poles. There is a G scale of five levels indicating storm levels with G0 being none at all and G5 being an extreme storm. G1 through G5 equate to KP5 through KP9, and you’ll find either number reported with various apps and websites. Finally, there is the Bz, which is the strength of the Earth’s magnetic field in the north-south direction. Positive numbers are northward, and negative numbers are southward. For the northern hemisphere, this means that a positive Bz will deflect most solar activity before it has a chance to interact with our upper atmosphere, resulting in a weak Aurora Borealis. A low Bz in the negative numbers means a weaker magnetic field on the northern pole, and thus much stronger northern lights. Many aurora apps only report the Kp or G-scale, which is not very useful without the Bz. In fact, I find the Bz to be more important for my area than the Kp. I’ve seen strong Kp7 and higher with a positive Bz that resulted in no observable aurora with my camera, and I’ve seen very weak Kp2 or Kp3 with a very negative Bz that resulted in beautiful blue and red spikes in the camera!

Northern lights seen from the base of Mt. Kineo on the North Bay of Moosehead Lake in Maine, October 8, 2013, 20:37

The camera captures a lot more than the naked eye can see. The human eye does not see a lot of color at night. We see green aurora the best, but it looks faint white. Red and blue really can’t be seen at all, although the camera will capture it. So you really have to take some test shots with your camera to see what’s out there and don’t rely on just your vision. A good friend and fellow night photographer, Mike Taylor, wrote an excellent article on this topic that I recommend reading:
http://earthsky.org/earth/will-you-see-colors-in-an-aurora

Camera settings vary wildly depending on the moon phase and brightness/speed of the aurora. When it is moving rapidly, you need a very wide aperture and shorter shutter speeds of 5 seconds or less. A prime lens of f/1.4 or f/1.8 is best in those circumstances. When the aurora is moving slowly you can get away with f/2.8 to f/4 and longer shutter speeds. ISO will range from 400 to 6400 depending on all the rest. It’s a good idea to experiment and try several exposure combinations as the brightness and speed of the aurora will likely vary while you are shooting.

For more information on the Kp index, G-scale, and latitudes they reach, check out these sources:
https://www.spaceweatherlive.com/en/help/the-kp-index
http://darksitefinder.com/reading-aurora-charts

Here are some good resources for aurora reporting and predictions:
http://www.aurora-service.org 
http://www.softservenews.com
http://www.solarham.net

And my favorite mobile app for alerts (screenshot):
Northern Lights Aurora Alerts

Northern Lights Aurora Alerts

Airglow

Airglow is similar to aurora and often confused for it, but instead of forming in a ring or oval around the magnetic poles it is uniform across the entire sky, often in large, sweeping bands. It is also less structured without spikes and moves much more slowly because it is not caused by solar wind. It is too dim to be seen by the naked eye, but can appear in ripples of alternating green and purple in a long timelapse. You’ll often capture it in typical Milky Way exposures during a new moon.

Here is a good article detailing the differences between airglow and aurora:
https://www.realclearscience.com/articles/2016/11/05/whats_the_difference_between_an_airglow_and_an_aurora_110077.html

Meteor Showers

There are several notable and predictable meteor showers every year, and they are a lot of fun to observe and photograph! Some years are better than others with the moon phase, and of course the weather is always a factor. PhotoPills has an excellent guide and calendar that they update every year so I recommend starting there: https://www.photopills.com/articles/meteor-guide

Meteor Shower Guide (iPhone only) is a great app for looking up meteor shower dates, intensity, and conflicting moon phases. 

PlanIt! for Photographers also has a great meteor showers planner.

Meteor Shower Guide

Eclipse information on the Planner map of PhotoPills

Eclipse list in PhotoPills

Solar and Lunar Eclipses

PhotoPills has a solar and lunar eclipse module that can help you plan the best time and location. Since they already have detailed articles on the subjects, I’d recommend starting there:
https://www.photopills.com/articles/lunar-eclipse-guide
https://www.photopills.com/articles/solar-eclipse-guide


Discovering the Night Sky

Here are a few prominent features of the night sky, to help you orient yourself during any season and find the Milky Way. The galactic center is not always visible during every hour of the night or every season of the year, as we shall soon see. These constellations will help you identify the direction and location of the Milky Way in the northern hemisphere, even if you don't have a compass, GPS, or smart phone with you.

Big Dipper

Most people know what the Big Dipper or Ursa Major looks like. It is one of the most visible and easily located constellations in the night sky. It is visible every night of the year in most of the northern hemisphere, but can be behind trees and obstacles near the horizon during the fall and winter months.

Little Dipper

If you draw an imaginary line from Merak and Dubhe, the two stars forming the right side of the Big Dipper, to the next brightest star in the sky, you will find Polaris, or the North Star. It is also the first star of the handle to the Little Dipper, or Ursa Minor. The night sky rotates counter-clockwise around Polaris. This is good to know for star trails later on. It's also an easy way to get a bearing without a compass.

Cassiopeia

Cassiopeia sits in the middle of the Milky Way, between Polaris and AndromedaIt is shaped like a W and the left middle segment is aligned with the Milky Way. The middle star of the constellation is often nicknamed Navi, in honor of astronaut Virgil (Gus) Ivan Grissom. It's his middle name spelled backwards, and was one of 36 stars used for navigation during the Apollo lunar missions.

Following the second star on the left side of Cassiopeia through Navi in the middle will point you toward the photogenic galactic core of the Milky Way, closer to the horizon in the northern hemisphere. You can almost draw an imaginary line from Shedir and Navi in the right middle segment and extend it to Polaris in one direction and the Andromeda galaxy in the other direction (it's not really that straight a line, haha!). You can’t see Andromeda with the naked eye, but it will show up in photos with the right exposure and dark enough skies.

Teapot

In the constellation Sagittarius is an asterism called the Teapot. It’s a great method of locating the galactic core or center of our galaxy, the Milky Way. It sits at the mouth of the teapot, like steam drifting upward! It is usually close to the horizon in the northern hemisphere, and not visible during the winter months.

Orion

During winter when the core of the Milky Way is not visible, Orion the Hunter and the Winter Triangle are visible, making great photographic subjects.

Winter Triangle

The Winter Triangle is another asterism, made up of stars from several different constellations. It consists of Procyon, Betelgeuse (the left shoulder of Orion), and Sirius (the brightest star in the night sky). All three of these are great stars to manually focus on during the fall and winter, roughly October through April in the northern hemisphere.

Summer Triangle

There is also a Summer Triangle that is nearly directly overhead all night long during the summer, but it is visible for some hours along the horizon throughout the spring and fall in the northern hemisphere. It rests in the middle of the Milky Way between Cassiopeia and the Teapot, and consists of Altair, Denob, and Vega (the third brightest star in the northern hemisphere, Arcturus is second). These also make great stars to manually focus on.

Putting It All Together

Taking what we now know of these constellations and how to find the Milky Way, here is what the sky looks in summer and winter in the northern hemisphere. South is at the bottom of the circle, and north is at the top.

Summer Sky

Winter Sky

Milky Way

The Milky Way changes orientation and elevation throughout the year as the earth pivots on its axis during our seasons. Here in New England, the galactic core rises from the horizon around 132° on the compass dial in the early morning hours before astronomic dawn in the spring, and the Milky Way forms a nice low panorama in the sky. By summer it is visible for much of the shorter nights but is oriented up and down and passes directly overhead around midnight or a little later, about 165° to 212° on the compass dial. In the fall the galactic center is visible right after astronomic dusk and sets below the horizon very quickly, still standing straight up and down and passing directly overhead, from 206° to 228°. In the winter, the dimmer portion of the Milky Way (one of the spirals we live in), passes directly overhead and settles into a very wide arch around 180° of the horizon. Quite often light pollution on the horizon prevents you from getting a very good panorama of it though. It’s easier to see this by changing dates and times in Stellarium or PhotoPills than capturing it in a photo, but here are some examples.

March, 4:17 AM

June, 11:24 PM

September, 8:26 PM


In the Field

Camera Equipment

Photographing the night sky is not difficult, but it is one field of photography where the right equipment absolutely makes all the difference. Getting sharp photos of dim moving objects like stars and the Milky Way is a lot more demanding than well-lit subjects during the day or with artificial light. A good baseline exposure for the Milky Way on a full frame sensor with dark skies is 14mm, f/2.8, ISO 4000, 25 seconds, and then tweak your settings from there.

Full Frame Sensor

Sensor technology continues to improve with every new generation, getting more sensitive with less noise at high ISOs. Generally, full frame cameras have an advantage over crop sized and smaller sensors due to the size of each pixel being larger and able to capture more photons in the same time frame. Sensor size, pixel density (number of megapixels), and in-camera processing all determine the quality of image at high ISO. You want a camera that can shoot cleanly to ISO 2500 at least, and preferably ISO 3200 to 6400 for very dark skies. Some newer mirrorless and crop sensor cameras are quite capable of this, particularly by Sony and Fuji.

Focal Length / 500 Rule

Wide angle lenses let you use longer exposures at night without stars streaking. A frequently used rule of thumb is to divide 500 by your focal length for the maximum number of seconds you can use for an exposure and still get acceptably sharp stars. It’s a relative figure—stars don’t appear to move as fast near the north star, but the further away from Polaris and the closer to the equator you get, the faster the stars appear to move. If you don’t have a 35mm full frame sensor, divide again by the crop factor (1.6 for Canon crop sensor DSLRs, 1.5 for Nikon crop sensor DSLRs, and 2 for some mirrorless cameras). 14mm to 35mm on a full frame sensor is best for Milky Way photography. 50mm and higher usually need a tracker to avoid streaking at long enough shutter speeds.

Here are some examples:
500 ÷ 14mm on a full frame sensor = 35 seconds
500 ÷ 24mm = 20 seconds
500 ÷ 18mm ÷ 1.6 for a Canon crop sensor = 17 seconds
500 ÷ 50mm ÷ 2 for a mirrorless sensor = 5 seconds

I often subtract another 5 to 10 seconds from these estimates to ensure sharp stars when shooting along the horizon, especially when printing larger than 12" x 18" from a high resolution sensor. For timelapses and star trails a small amount of streaking won’t matter.

NPF Rule for Sharp Stars

There is a much more complicated and accurate exposure rule for those that are interested called the NPF Rule. As sensors get more dense with more megapixels, or larger such as medium format, the “500 Rule” falls short. This is why I often subtract 5 to 10 seconds from the result. A more accurate formula would be: (35 x aperture + 30 x pixel pitch) ÷ focal length = shutter speed in seconds

To figure out the pixel pitch of your camera, divide the sensor’s physical width in millimeters by the number of pixels in width, and multiply by 1000 to measure it in microns. For example, a Nikon D810 is 35.9 x 24mm and 7360 x 4912 pixels. 35.9 ÷ 7360 x 1000 = 4.88 μm (rounding up).

Therefore, a 20mm f/1.8 lens on a 36MP D810 would equal about 10.5 seconds: (35 x 1.8 + 30 x 4.88) ÷ 20 = 10.47 (rounding up)

The 500 Rule would say 500 ÷ 20 = 25 seconds, which has significant streaking in the corners on a 36MP camera if you zoom in or print large. You could probably get away with 15 seconds though and look acceptably sharp.

Don’t forget your “order of operations” from high school math class for the above formula: solve the multiplication before the addition or you won’t get the correct results!

Check out this dedicated article on the NPF Rule for screenshots of how to use it in qDslrDashboard and PhotoPills (no complicated formulas necessary!): http://galleries.aaronpriestphoto.com/Articles/NPF-Rule-for-Sharp-Stars

Aperture

A wide aperture of at least f/4 is best for Milky Way photography, preferably f/2.8 unless your camera is capable of extremely high ISOs. Not every lens is sharp at f/2.8, and many f/1.4 and f/1.8 primes are not sharp enough until stopped down to at least f/2. Many lenses produce oblong and pear shaped stars in the corners at wide apertures, this is known as coma and is not easily fixed in post-production. Distortion and vignetting are much easier to fix.

A few notable lenses are exceptional at wide apertures with very little coma, particularly the Nikon 14-24mm f/2.8, Tamron 15-30mm f/2.8 VC, Rokinon 14mm f/2.4 SP (manual focus), and Tokina 11-20mm f/2.8 Pro DX (for crop sensors). Generally speaking, lenses with an aspherical lens element have better coma control.

ISO

As mentioned previously, ISO 2500 to 6400 is a good ISO range for the Milky Way with dark skies. Conventional wisdom would dictate using as low an ISO as possible for less noise, but night photography is very different. Unless you are using a tracker or stacking images for longer exposures, we have to use very high ISOs to capture enough detail of the Milky Way. Ideally you are aiming for -6 to -7 EV exposures for good Milky Way details with no light pollution or moonlight.

http://photonstophotos.net/Charts/PDR.htm is a good resource for suggested low light ISOs of various cameras. 

Ian Norman has an excellent article on finding the best ISO to use for your camera too:
http://www.lonelyspeck.com/how-to-find-the-best-iso-for-astrophotography-dynamic-range-and-noise

Many Nikon and Sony cameras are highly ISO invariant, where the ISO doesn't really matter very much. You can adjust exposure in post-production and get about the same amount of noise as adjusting the ISO in camera, at the expense of dynamic range. Here is an article by Spencer Cox on that topic: https://photographylife.com/iso-invariance-explained

White Balance

White balance won’t affect RAW files, just JPEGs, TIFFs, and the preview image on the camera’s rear LCD display. I find a proper white balance is useful when shooting in the field though to get a better preview of my image and exposure, since the histogram won’t be of much use for really dark scenes. A manual white balance of somewhere between 3000° and 4000°K is best for the Milky Way. I’m usually around 3450° or 3570°K on my Nikon. It doesn’t have to be precisely accurate, you can change it in Lightroom or Camera RAW later. If shooting timelapses and editing using LRTimelapse, a manual white balance is preferred for consistency over auto white balance.

LCD Brightness

The brightness of the rear LCD on your camera will probably be way too bright for reviewing images at night. It will fool you into thinking your photos are exposed brighter than they really are, and it will annoy others shooting near you! I dial it down until I can barely see the difference in shade between the two darkest colors (black and dark gray) in the sample palette, about -2 to -3 on a Nikon.

Viewfinder Cover

It’s a good idea to cover your viewfinder or close the curtain to it for long exposures at night. During the day stray light through the viewfinder usually only affects your meter reading and not the image itself, but during long exposures at night it can show up on the edges of your frame, particularly if you have a light source behind you or a headlamp or flashlight hits the back of your camera. Many cameras ship with a little plastic cover (that soon gets misplaced), sometimes on the camera strap. You can also cover your camera with a hat, coat, etc.

RAW vs. JPEG

RAW files store much more data than JPEGs, which is important for good post-processing later of night photos, particularly the Milky Way. If your camera has a choice between 12 or 14-bit RAW files, go with the highest quality and image size possible for better noise reduction and shadow boosting later.

Noise Reduction

There are two types of noise reduction in your camera’s menu: high ISO noise reduction and long exposure noise reduction. High ISO noise reduction doesn’t apply to RAW files, only JPEGs and the embedded preview image, so I leave it disabled to avoid extra processing time by the camera. Long exposure noise reduction applies to all file types and removes hot pixels from sensor heat during long exposures (typically 8 seconds or more on most cameras). It doubles your exposure time and shoots the second photo with the shutter curtain closed, then removes any exposed pixels it finds in the second shot from the previous one before saving the file.

For a 30 second photo, a minute isn't a long wait, but for a 4 to 8 minute ground exposure, it can feel like eternity! Night photography is a craft that takes a lot of patience to master though, and I usually leave long exposure reduction enabled unless I’m shooting a panorama or timelapse.

If you are shooting a panorama or especially a timelapse for star trails, you can’t have a long interval between shots for long exposure noise reduction. Instead, you can shoot a “dark frame” at f/22 with a lens cap on to capture nothing but hot pixels, and then apply it to your light frames later.

Pixel Fixer is a great program for this if it supports your camera model because it can work on RAW files. Other programs like Sequator, Starry Landscape Stacker, and StarStaX can also use dark frames as TIFFs. More dark frames make for better analyzing, but not every program can do this. I usually shoot somewhere between 10 and 30 dark frames for every shutter/ISO combination that I used during the night, if I’m not using long exposure noise reduction in camera.

Image Stabilization

Disable any image stabilization features your sensor or lens might have. Nikon calls it VR for Vibration Reduction, Canon calls it IS for Image Stabilization, Tamron calls it VC for Vibration Compensation, Sony calls it OSS for Optical Steady Shot, etc. Typically you want this feature turned off when using a tripod, and it won't work with the long exposures we shoot at night anyway.

Pentax is the exception as some of their DSLRs have a unique feature for astrophotography called Astrotracer. It couples the SR or Shake Reduction sensor stabilization system with their external GPS unit to rotate the sensor and track the stars during a long exposure. It sounds like a marketing gimmick, but it actually works! I have seen 5 minute exposures that were tack sharp without a tracker. 

IBIS or In-Body Image Stabilization on some new mirrorless cameras might be the exception to this, you'll have to experiment and see if it helps or hurts image sharpness.

Focus

Critical focus is necessary for sharp stars. Infinity is usually not where it is marked on your lens. Autofocus on most cameras will not work on dim stars. The best method is to manually focus on a very bright star using live view on a tripod. If you have good enough eyes, you can roughly center a star in the viewfinder and then switch over to live view. Live view won’t see any stars until at least 5x usually, and then you can pan around a bit until you find it and zoom in again to 10x or higher. Don’t zoom with your lens, most zoom lenses have “focus breathing” where they shift focus slightly as you zoom. Manually adjust your focus until the star in live view is as small a pixel as you can get it with no soft edges or halos around it. Make a note of where this point is on your depth of field scale and tape your lens down for the night with masking tape or anything that won’t leave a sticky residue, unless you are going to do focus stacking later.

If you use qDslrDashboard on your smartphone or tablet, there is a live view filter called Canny that can help focus the outline of stars. Make it as small a circle as you can. I find this easier than using the smaller LCD screen on the camera and trying to see a pixel.

The best method is to use a Bahtinov Mask filter. It's very fast and easy to set your focus with no guess work. Ian Norman sells them on his website here: http://www.lonelyspeck.com/sharpstar/

Focus Blending and Exposure Blending

Often a single exposure of the Milky Way does not have enough depth of field or a long enough shutter speed for ground details. To get around this you have to shoot a longer exposure that is sometimes refocused for a closer object. I often lower my ISO or narrow my aperture by a stop or two and shoot very long exposures of the ground to combine later in Photoshop. The exposure difference varies on light pollution, ground details (woods, snow, grass, water, etc.), and moon light, but sometimes it is 3 or 4 stops more than the exposure of the stars, which can mean a shutter speed of several minutes if I also lowered my ISO for less noise or closed my aperture for more depth of field.

Exposure Stacking and 10x Rule

One method of reducing noise for the night sky is by shooting several [relatively] short exposures at very high ISOs and then averaging them to reduce the random noise. By masking out the ground details, and aligning the stars in each frame, you can achieve a much longer shutter speed without using a tracker and still have pin-point stars. A starting point for this is what I like to call the "10x Rule" to make it easy to remember: 10 exposures @ 10 seconds apiece & ISO 10,000. As with the 500 Rule, you'll want to experiment with this to get the best results for your camera sensor and focal length. If you use the NPF Rule in PhotoPills, choose Accurate instead of Default for the recommended shutter speed.

The more images you use, the more signal-to-noise ratio (SNR) you will get and thus less noise, but you will get diminishing returns--quadrupling the number of images will double the SNR. So the difference between 1, 4, and 16 frames is quite dramatic, but you have to get to 16 to be appreciably better than 4, and 64 to be better than 16, and so on. The sweet spot is somewhere around 9-12 images (without a tracker anyway): too many and you have difficulty aligning the stars, too few and you won't have enough data to average out the random noise.

The post-processing of all this is obviously far more complex than a single image, or blending two exposures of sky and ground. You should still take a separate long exposure of the foreground for this technique, and you can even average several long exposures of the ground if you have the time to take them, but you won't have to worry about aligning the ground shots of course. Fortunately there are two programs that have been made in the last few years that make the post-processing and alignment of the sky images much easier: Sequator for Windows and Starry Landscape Stacker for Mac. There are many tutorials and videos on how to use them that are beyond the scope of this article.

Low Level Lighting

Light painting with a flashlight or bright Xenon light used to be a pretty popular technique for lighting a foreground and avoiding the need for long exposures at low ISO to reduce noise. It is disruptive to wildlife and other photographers however and the practice of light painting is generally frowned upon today, even banned in some places. A much better method with newer technologies like LED panels is called low level lighting, where you use a constant light source turned down low so it is barely perceptible to the human eye but quite dramatic in camera with 15-60 second exposures. If it's done well, you can capture sharp stars and a well-lit foreground in a single image without the need to blend two different exposures. You can still combine it with the above techniques for even better image quality however--stacking or tracking sky shots for less noise and averaging several ground exposures at the same time to reduce noise. Royce Bair and Wayne Pinkston have put together an excellent website and resource on this topic with recommendations for LED panels and other gear: http://lowlevellighting.org/

Camera Support

A sturdy tripod is a must for long exposures, particularly in the dark where you are bound to bump it or knock it over. Pay close attention to those shooting around you and give them space, both for this reason and to avoid stray light from ruining their shots. I recommend not raising a center column at all if you can avoid it to keep your center of gravity low and your tripod less likely to get knocked over, especially if you are leaving it for a while for a timelapse.

A good ballhead is easier to compose with in the dark than a geared video head, where you might not be able to tilt high enough very easy or use in portrait orientation. Panning/gimbal heads on a leveling base also work very well and are my preference as I often shoot panoramas of the Milky Way. A major advantage over a ballhead is that you have independent control of each axis, so you don't have to worry about leveling your camera again if you want to change your composition a little bit left/right or up/down. I use a Nodal Ninja RD8-II and RD16-II indexed rotator underneath my panning head so I can feel the click-stops in the dark and don't have to turn on a headlamp as often when shooting a panorama at night.

Whatever you use, it’s a good idea to be comfortable using it during the day before struggling with it at night and turning the wrong knob, throwing a camera or lens off balance and damaging something. Everything is more challenging in the dark, particularly if it’s cold and you are wearing gloves!

Trackers

Once you graduate beyond single exposures, blended exposures, and stacked exposures, inevitably trackers are the next level in the pursuit of image quality. It takes some extra time to set them up as they have to be polar aligned so they move with the sky and counter Earth's rotation, letting you shoot long exposures of the stars with longer focal lengths at low ISOs--no need for the 500 Rule or NPF Rule anymore! Polar alignment is easier to achieve in the northern hemisphere because we have Polaris or the North Star as an aid and it's quite close the north celestial pole (NCP) and easy to find. Two affordable and popular trackers are iOptron's SkyGuider Pro and Sky-Watcher's Star Adventurer. They have several tracking speeds for stars, moon, and sun (never point a long lens at the sun without a proper solar filter!!!). You need to disable tracking when shooting foreground exposures of course, or they will be blurry from the tracker's movement.

Dew / Frost

The bane of night photography: dew and frost! Without getting too scientific, dew forms when an object radiates heat faster than it can absorb it, causing water vapor in the air around the object to condense on it. If the dew point is below freezing, you get frost instead. Practically speaking, the front lens element of a wide angle lens is the perfect candidate! Dew and frost will form on your lens before you see it on anything else and you won’t even notice it until you see your photos starting to get fuzzy and dim later at home.

The best solution is to keep the lens warmer than the ambient air around it so dew can’t form in the first place. Hand warmers rubber-banded to the lens barrel and close to the front lens element are a good solution, as are electric dew heaters like astronomers use. Once dew has formed, it is hard to wipe it off or get the lens warm enough to dry out off with just a hand warmer. Wrap a sock or scarf around the hand warmer to keep the heat close to the front lens element. You will undoubtedly knock your focus out while doing this, so either focus afterward or tape your focus ring down first.

I use a Dew-Not heater strip (you can get different lengths from Amazon.com) plugged into a DewBuster controller. 

Filters

UV and “protective” filters make matters worse as you are adding another very thin layer of glass with an air pocket behind it. They dew up faster than your lens will. I recommend taking them off at night to avoid dew and glare, unless you are shooting near sea spray or in ocean fog, in which case a filter is sometimes easier to clean afterward.

A lens hood will also help prevent dew on longer lenses. Many wide angle lenses have a fixed lens hood already.

There are a couple filters that can be useful for night photography however:

Didymium glass can reduce the color or wavelength of light from sodium vapor lamps to cut down on light pollution. It's not a magic pill to fix light pollution, but it can help.

A fog filter like the Tiffen Double Fog 3 can reduce the dimmest stars and enhance the brighter stars to give you better star glow. You will lose image sharpness of course, but you can mask a foreground exposure without the filter in Photoshop to add back landscape detail. Royce Bair has an excellent example on his blog: http://intothenightphoto.blogspot.com/2014/03/increasing-star-glow.html

Battery Power

Long exposures will eat up battery life quickly. Don’t be surprised if you get far fewer shots than you would normally get during the day before your battery dies. Cold temperatures make batteries even less efficient. It’s a good idea to carry a couple spares in your pocket or inside a coat near your body to keep them warm. During the winter you can swap out batteries more often and you’ll find an almost dead battery has quite a bit of juice left over after it has warmed up again.

A vertical grip with a second battery makes a big difference at night, particularly when shooting long timelapses. If you want to shoot a single timelapse that is longer than 3 or 4 hours without interruption you will probably need to run off external power. There are several ways to do this. Some newer mirrorless cameras can be powered via USB. Others need a dummy battery with attached power cord inserted from the manufacturer. Tether Tools makes an excellent Case Relay Camera Power System for many cameras, just choose your manufacturer and model to get the right camera coupler part number. You'll still need a battery, which Tether Tools also sells, as does Goal Zero and Anker if you need even more power.

Since I often use a dew heater, motorized head, slider, and other electronics for overnight shoots I standardized on 12v power to run all my devices. I have a 100Whr Goal Zero Sherpa 100 that weighs 1.9lbs and is easy to hike with but has a lot of power, with a Nomad 20 solar panel to charge it during the day (daisy chaining two or more panels charges even faster). I put Anderson Powerpole connectors on the ends of all my cables and I use a power distribution block to plug in whatever devices I want to use for the night. My Nikon won't run off 12v though so I bought a DROK 12v to 7.5v step down converter to power my camera. With this method I can power everything off a much larger lead acid battery for several days without needing a USB port. You'd have to see what voltage your camera uses if you go this route and make your own cables.

Intervalometer

An intervalometer allows you to shoot a photo in regular intervals to speed up later as a video, a.k.a. timelapse. Most Nikon cameras have a built in intervalometer in the menu, but it’s limited to 999 frames on all but the most recent models. That should be plenty for most scenarios.

Canon users can try out Magic Lantern firmware, if you are brave and your model is supported. There are also many external remotes that offer an intervalometer feature, too many to list here in detail, from simple to complex.

Promote Control is one of the more popular complex remotes for HDR bracketing, focus stacking, timelapse, and bulb ramping.

Timelapses

Timelapses are a lengthy discussion and deserve a dedicated article, so this is only a brief introduction with a few resources to check out if you are interested. Timelapses are easy to shoot between astronomic dusk and dawn because the exposure remains consistent. Any intervalometer with manual exposure will work. However, shooting sunset into Milky Way or the opposite into sunrise is considered the holy grail of timelapsing due to the complexity. It usually involves some form of exposure ramping or bulb ramping (shifting ISO/exposure in bulb mode). Here is an article on exposure ramping: http://galleries.aaronpriestphoto.com/Articles/Manual-Exposure-Ramping

DslrDashboard is a good app for “easy” holy grail timelapses and worth investigating, especially if your camera has built-in WiFi. There is also a cheap battery powered wireless router that can be used for cameras without WiFi on that website.

LRTimelapse is a powerful program for gradually changing Lightroom/ Camera RAW edits over time (such as white balance or exposure) for both panoramas and timelapses.

Ramper Pro is a new, high-end timelapse controller with motion control, interval fairing, light sensor, histogram monitoring, 3D support, and more.

Dynamic Perception and eMotimo build some very affordable and easy-to-use sliders and motion control robotic heads.

Star Trails

Star trails are very closely related to timelapses, in that you capture the images with the same process, but instead of playing them back fast for a video you stack them into a single image to see the star movement. You can also use a single long exposure instead of stacking multiple short exposures. There are merits to both methods. I wrote a longer article detailing why I prefer stacking over a single long exposure:
http://galleries.aaronpriestphoto.com/Articles/StarTrails

I find that using the same exposure as you’d use for the Milky Way produces too many stars to look good when stacked. It’s better to knock your ISO down 2 or 3 stops. This also means that star trails look good with a little bit of moon light as that also reduces the number of visible stars. I like starting or ending my star trails timelapse during astronomic twilight to get some of the cobalt dark blue color in my skies. I’ll let it overexpose at the beginning or end and choose how many frames I want to use later when stacking to get the brightness I like.

A short interval is important to prevent gaps in your star trails. This means disabling long exposure noise reduction.

StarStaX is an excellent free program for stacking stars. It supports dark frames and has features for gap filling, comet trails, reverse trails, and more. Currently it cannot export a 16-bit file, only 8-bit, but it does support TIFFs (both import and export).

Advanced Stacker Plus is a photoshop plugin, and lives up to it’s name. It’s my preferred method of stacking star trails. I recommend taking Steven Christenson’s online workshop from his website on how to get the most out of it.

Photoshop’s stacking modes can also be used natively, but the two programs mentioned are much faster.

Star Tracer (Windows only) is a great program for extending star trails if you didn't shoot enough frames, and also for gap filling.

Sathya Narayanan has made a couple Photoshop scripts that are great for creating vortex star trails and creative effects: http://liketheocean.com/night-photography/scripts-to-make-your-star-trails-awesome/

Outdoor Equipment / Safety

Obviously a flashlight or headlamp is a necessity for night photography shooting. I recommend one with a red LED mode to preserve your night vision. Spare batteries and an extra flashlight are very wise precautions.

Here are some more recommendations for extended night photography:
• Whistle (many headlamps and camera backpacks have one already)
• SOS and slow blink modes on flashlights (cell phones don’t always have service and batteries die)
• Trash bag, plastic bucket, etc. to set your backpack on or in to prevent dew, mud, mist, etc. from getting your gear wet
• Rain jacket during the summer or scarf / small blanket during the winter to wrap around the camera and keep dry / warm during long timelapses
• Extra layers as it can get very cold at night: boots, hat, gloves, extra jacket, etc.
• Water, snack, and a first aid kit are always a good idea to have nearby, or on you for a long hike


More Night Photography Resources

Antoni Cladera of PhotoPills interviewed several well-known night photographers and put together an excellent resource on shooting the Milky Way: http://www.photopills.com/articles/how-shoot-truly-contagious-milky-way-pictures

Two more good articles on using the PhotoPills app to shoot the Milky Way:
http://www.photopills.com/articles/how-plan-milky-way-using-2d-map-centric-planner
http://www.photopills.com/articles/how-plan-milky-way-using-augmented-reality

David Kingham has a great eBook on shooting the night sky that I highly recommend:
http://craftandvision.com/products/nightscape

I keep a list of my favorite apps and websites for iPhones, iPads, Androids, Windows, Mac, etc. on my own website here

Workshops

Visit my workshop page for a schedule of upcoming workshops. I'm also available for one-on-one sessions and small groups.


Thanks for reading and feel free to share this page with others! Happy shooting!!!

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