Night photography, especially star trails and milky way photography are becoming much more accessible. Once upon a time you needed the latest best full-pro camera body and an expensive fast pro-level lens to to have a hope of capturing the milky-way in all its glory. Technology has marched on and just about any current generation camera body, whether full frame, DX, APS-C, or Micro 4/3 can do a competent job.
Lenses are different story.
Note: This article is designed for people diving into milky way photography for the first time (for example, taking my class) who need helping picking a beginner milky way lens. For those looking for a much more technical and in-depth article, check out Lonely Spec’s milky way lens article. It gets as technical… They also offer first hand recommendations for lenses for various situations.
TL;DR: Picking a Beginner Milky Way Lens
Aperture: You need a lens with an aperture of at least f/2.8 to reasonably take milky way photos.
Focus Length: Because you can’t back up, you will need a lens with a 70 degree field of vision or wider. On full frame, you need a 24mm or wider, on DX or APS-C you need an 18mm or wider and on Micro-4/3 you need a 12mm or wider. For beginner milky way photography, wider is usually better.
Focusing: Focusing at night is hard. Auto-focus doesn’t work most of the time.
- Kit Auto-Focus Lenses: avoid if possible… Their focusing rings are usually terrible and they normally don’t have focus scales so you just have to guess and check.
- Fly-by-Wire Lenses: Can work great or can be terrible. I’ve seen some of the kit level Sony lenses for the A-6XXX series be absolutely impossible to focus at night consistently. I’ve seen others higher end fly-by-wire lenses (Sony included) work great. The only way to know is to test in the real world at night…
- Manual Focus Lenses: Usually work great at night since their focusing ring is designed to be used by hand and they normally have an accurate focus scale.
- Pro Auto-focus Lenses: Workable normally. They normally have a focus scale that might or might not be accurate. Their focusing ring is designed to be used some of the time at least.
Picking a Beginner Milky Way Lens
Photographing the milky way is demanding. Light levels are extremely low and, the milky way is a fixed size. You can’t back up to make it smaller in the frame.
From experience here are the core criteria that are needed:
- Fast Aperture
- Consistent Manual Focus
- Wide to Ultra Wide Field of View
Lets start by defining what we mean. A fast aperture means an aperture that lets in a lot of light. Smaller f numbers are “faster”. On a given lens, a smaller f number means a bigger hole in the lens to let in more light. So, f/22 is a slower aperture than f/2 because f/22 is a smaller hole than f/2.
In this case we are interested in your lens’ fastest (smallest f number) aperture. So, for example, I have a Nikon 14-24mm f/2.8 lens. The name of the lens normally contains the fastest aperture the lens can handle. I can use my Nikon 14-24mm f/2.8 at an aperture of f/2.8 at any zoom setting (at 14mm, at 24mm or anywhere in between).
Variable Maximum Aperture
Some lenses, in particular entry level “kit” lenses and less expensive non-pro upgrade lenses have variable maximum apertures. The lens model will list a range of apertures as a part of it. For example, many companies sell a kit level 18-55mm lens. Most are sold as 18-55mm f/3.5-f/5.6. That means that at some zoom ranges the “fastest” the lens can go is f/5.6. At other zoom settings it can go to a faster aperture of f/3.5. Normally, you can access the faster end of the range at the wider end of the zoom range.
If you are curious why this is the case, it is because it is more expensive (i.e. more difficult) to design a lens with a constant aperture. Thus, most consumer level gear (“kit lenses”) have variable apertures.
There are other considerations if you want to get more technical. It turns out for astrophotography we want to gather the maximum number of photons possible. The f-stop just tells us how big our aperture is relative to our focus length, not how big it is in absolute terms.
The “clear aperture” is what tells you how many photons are gathered in an absolute sense. The super simplified version is that for a given aperture (say f/2.0) the longer the focus length the physically larger the aperture and the more photons will hit the sensor even though both lenses at a given aperture produce the same exposure.
See the Lonely Spec article for the technical details.
What You Need
For the purposes of learning milky way photography, you should have an f/2.8 lens at least. An f/2.0 or f/1.4 lens is even better. We are working in extremely low light. You can get away with an f/4 lens by increasing your ISO if you have one of the latest full frame cameras and are willing to accept considerable noise.
Consistent Manual Focus
Focusing at night is hard. Auto-focus is usually useless unless you have a foreground subject you can light up and focus on. That means, we will be focusing manually and this is where things get a little more complicated. First things first: lets talk about manual focusing in general.
Manual Focus Lenses
Once upon a time, there were only manual focus lenses. These lenses were designed to allow the photographer to quickly and accurately acquire focus by hand. Their focus rings had a long “throw” (that is, they turned a long way from closest to furthest focus allowing finer control of focus). Manual focus lenses (generally) had accurate focus scales on their focus ring too. You could actually focus by measuring the distance from the lens to your subject and then dialing the lens to that distance on the sale. And finally, manual focus lenses usually have a calibrated infinity stop. That means, if you turn the lens all the way to the furthest focus where the focus ring stops turning, you are focused to infinity.
If you have a manual focus lens, antique or modern (such as the Rokinon 14mm lense), then your lens will likely be reasonably easy to focus at night (as easy as it can be anyway).
Pro Auto-focus Lenses
Modern auto-focus lenses are a different beast entirely. Most modern auto-focus lenses still have a physically coupled focus ring (see fly-by-wire below for the alternative). When you grab the focus ring you are mechanically moving the lens elements around. In that way, they are similar to manual focus lenses. From there, things diverge and will depend on the particulars of the lens in question.
Pro level auto-focus lenses usually have a (somewhat) accurate focus scale on them. Their focus throw is usually shorter than manual focus lenses but still usable, especially on wide lenses where tiny changes in focus are less critical. Auto-focus lenses generally don’t have a hard infinity stop. Modern cameras allow the auto-focus system to find focus at infinity. That means, you can focus PAST infinity. Without a calibrated infinity stop, you can’t simply turn the lens to infinity and get the stars in focus.
All that said, modern professional auto-focus lenses are quite usable, especially with a little experience of how to use the (usually tiny and somewhat inaccurate) focus scale. I use a number of modern auto-focus lenses for milky way photography.
Kit Auto-focus Lenses
Like their higher-quality (and more expensive) brethren, the pro auto-focus lens, kit lenses usually (but not always, again see fly-by-wire below) have a mechanically coupled focus ring and no infinity stop. Unlike pro lenses, most kit lenses don’t have a focus scale and their focus throw is tiny. They are designed not to be used in manual focus.
Kit level lenses can usually be made to work, but they can be quite frustrating for milky way photography due to their limitation and especially for first time milky way photographers.
A recent trend that is likely to continue are fly-by-wire lenses. These lenses do NOT have a mechanically coupled focus ring. Some (pro level in particular) may have a focus ring to grab, but it is just a switch that tells the camera to change the focus distance. Other lenses, especially the kit level lenses, may not have a focus ring at all. Focus is set from the camera screen by touch or with buttons on the camera body.
There is nothing wrong with fly-by-wire in principal and I’ve seen fly-by-wire lenses that make focusing at night easier than any of the other types of lens mentioned above. You simply dial the lens to the exact distance you want (including infinity) and it is right. In effect, good fly-by-wire lenses (and camera bodies – they are an integrated combo) are like having the most accurate focus scale possible with a calibrated infinity stop and super precise focus ring. The camera tells you the focus distance and it is repeatable making incremental changes in focus easy.
I’ve also seen fly-by-wire lenses that make it impossible to consistently focus at night due to basically terrible implementation (looking at your Sony and your terrible crop frame kit lens for the A6**** series).
In short, your mileage may vary. The best way to determine if your particular fly-by-wire lens will work is to go out in the dark at night and test in manual focus. If you find yourself wanting to throw the camera across the yard, you might have the wrong lens/camera combo to sanely focus at night.
You have probably noticed a lot of “generally” and “usually” in this section. That is because there are a HUGE number of lenses built by different companies. Even within lenses from one company for one camera there is a lot of variation from model to model. Some lenses may work great and others terrible. In the end, there are really only 2 ways to know if your particular combination will work:
- Talk to someone (or find them via google) that has used the combination before in this environment, or
- Go out and test the combination yourself.
Things can look great on paper and not work at all in the real world. Milky way photography is outside the scope that most manufacturers design and test for. We are going outside the safety zone defined by camera companies and are on our own.
Wide or Ultra-Wide Field of View
You can’t effectively back up from the galactic core unless you own a FTL ship. It is 15,519,380,0000,000,000 miles (you can just say “really far” instead of reading the number) away. Moving 100 feet, or 100 miles makes no appreciable difference in the distance, or therefore in the size of the milky way in your picture. To capture more of the milky way, you need a wider lens (or to shoot a panorama which adds a ton of complications).
What is a wide lens in this context? The galactic core (the part that is most interesting and pretty) spans about 70 degrees in the sky give or take. That means, your lens/camera comb needs a 70 degree field of view to capture the entire galactic core. This ignores the need to also capture some of the ground and any foreground subject it might contain.
To give you an example, this is an image from a 14mm lens on a full frame (crop factor = 1.0) camera shot in portrait orientation. That combination has about a 110 degrees of view in the long (vertical in this case) direction. With that much field of view you can frame the galactic core along with a good bit of foreground.
And here is a shot from a 38mm lens (zoom lens) on a full frame camera to give you an idea of how much narrower it is with approximately a 50 degree field of view. The only reason a foreground is included is because the galactic core is near the horizon from my point of view shooting up a steep hill. Note how much less of it is captured.
Time and Focus Length
The other consideration besides field of view is time. The earth is rotating. That means the stars appear to move. That is what lets us make star trails. For milky way photography, we do NOT want star trails. That means we need to keep our exposure time short enough that the movement of the stars is not apparent in the photo. The stars move at a fixed angular speed. That is, the stars move .25 degrees per minute. Closer to the poles (e.g. the north star) that movement is not obvious because a full 360 degree circle doesn’t cover much ground. Near the ecliptic (i.e. over the equator in the middle of the poles) the stars seem to move quickly because a full 360 degrees circle is covering the full width of the sky several times.
The long and short of this is that the bigger a patch of sky you photograph (i.e. the wider your lens) the longer your exposure can be before the apparent motion of the stars becomes obvious. With a telephoto lens, you are looking at only a few degrees worth of sky. A quarter degree per minute will cause the stars to move significantly in just 30 seconds. A 14mm lens on a full frame camera sees 110 degrees. An quarter degree per minute of motion in 30 seconds isn’t obvious in the resulting images.
Wider lenses let you get away with longer exposure times. That is a good thing when it is milky way dark.
What focus length (mm number) constitutes a wide or ultra-wide lens on a given camera depends on the size of the sensor, i.e. the crop factor. Without going into the gory details, here are is my recommended focus length range for your first milky way shooting experience with maximum recommended exposure time:
|Full Frame||Crop Frame||Micro 4/3||Field of View||Max Exposure|
The maximum exposure time is a rule of thumb. Some people may tolerate longer exposures while others will find the star trailing to obvious at these times. Again, the Lonely Spec article has a nice animation of different exposure times on the same lens if you want to see the effect in action.
Wrapping it Up
You can make almost any wide or ultra-wide angle lens work for milky way photography, but picking a beginner milky way lens can make your first milky way photography experience a lot easier and more fun.
Choose a wide angle lens. If you are on a full frame camera, go for a 20mm or wider lens if you can. If you are on crop frame look for a 15mm or wider. Stick to f/2.8 or faster (f/2.0 or f/1.4).
True manual focus lenses work great and most pro-level lenses are still good in manual focus. If you are considering using a fly-by-wire lens, it is a good idea to test in your back yard before heading out to a more remote and difficult to reach location.
He is a self taught experiential learner who is addicted to the possibilities that new (to him) gear open up. He loves to share the things he has worked out. Andrew started with a passion for landscape and night photography and quickly branched out to work in just about every form of photography. He is an ex-software developer with extensive experience in the IT realm.