Star Trails Tutorial
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floris
Registered: May 11, 2006
Total Posts: 4674
Country: United States

So a little while back I said I'd write up a star trails tutorial.. well, it ended up being pretty long. It turns out there's a lot you have to think about, and writing it all down took up lots of space. I hope you find it helpful, and I would love to get some feedback, as I think I might want to try submitting something like this to some magazines or something to see if I can get it to go anywhere (suggestions most welcome.. I've never done that before!).

Moderators: maybe we can get a sticky for this for a little while so people don't miss it?

The Midnight Hour – How to Shoot Star Trails

It’s that time in the evening, when the sun has set, the clouds have finished putting on their show, and the first stars are beginning to shimmer through the twilight blues. It’s one of the most peaceful and tranquil moments of the day, second only to predawn, but you’re probably packing your bag to make sure you get back to the car before darkness descends. Soon the stars come out in full force, lighting the sky with points of light stretching away for many light years. Take a minute and look up, it’s a wondrous sight. If you’ve never sat deep in the wilderness miles from civilization and simply watched the light retreat from east to west and the stars dance in circles around you, you’re missing out.

"Rocks Racing Stars" ~ The Racetrack, Death Valley National Park
The Tech: Canon 20D, 10-22mm
Exposure: iso 400, f/5.6, 2.5 hours over 5x 30 minute increments (my first real attempt), started soon after twilight

Enough with the poetry now, your question is of course, well, how do I actually photograph this incredible beauty? It’s likely you’ve tried, yet couldn’t quite capture the color, the delicate light dancing over the land around you, and the first twinkles of stars, and the subsequent circles traced out by the stars around Polaris. In this article I will share with you how to go about capturing that magic, from the preconception through to the finished product. Most of this article will concentrate on how to capture a stunning startrail photograph, though much of it is relevant to capturing that fleeting moment of twilight. This is a complex process involving more planning and technique than most photos, so sit tight and get ready to learn!

Note: I use a mac, so all my photoshop directions are for a mac, they’re probably similar for a PC.

The first step in creating a successful photograph is generally some sort of pre-visualization. The beauty of startrails and previsualization, is that they are very predictable. Eventually you will get a clear night at your desired location, and you’ll know exactly what those stars will do. Getting the right clouds, mist, or ethereal light requires more luck and patience to get exactly what you picture in your mind. And of course, once that happens, it will never happen quite that way again – it is unique. On every clear and calm night, however, startrails will look nearly identical to any other day (sure the constellations will be in different positions, but for nearly every application this won’t make a difference). As a result, a startrail photo can easily become cliché, the stars and sky will not be the unique part of your image. What will make your photo special, is where you chose to take, what the foreground is and how it relates to the circling heavens above. For me, startrails show three things: geometrical shapes, motion, and the revealing of an invisible force. As a result, I strive to find foregrounds that will resonate with those qualities, making for a final image that hopefully speaks to you on an emotional and/or intellectual level.

floris
Registered: May 11, 2006
Total Posts: 4674
Country: United States

Planning and Preparation:

Suppose you have now have an idea for what image you would like to capture. Now how do you go about doing it?

First, you’ll need to determine when is the appropriate time to shoot. Yes of course, at night. Ok, well, do you need the moon up so that you can get light on your foreground? If so, what phase should it be in (ie. How much light do you need for the foreground?). What time do you want to start shooting (ie. How much light do you want in the sky), so what time do you need the moon to rise at or set by? How high in the sky do you want the north star, if you want it in the frame (this will depend on the time of year). As you can see, there are a lot of questions to be considered, but fortunately there are also some guidelines you can follow. In the following sections I’ll give my advice for where you might start.

To summarize, you’ll need to consider these:

1. Location (far away from cities! City glow can ruin the sky and give you less stars)
2. Time of year
3. Moon phase
4. Moonrise times
5. Sunset/sunrise times
6. Weather predictions (you’ll want a clear night)

Before you head out the door:

The very first step in creating a successful twilight or star-trail image is preparation. You might be leaving your home, car or tent in the last hour of light, but you’ll be returning long after dark. At the very least you should make sure you have a way to get back safely!

Here’s a list of non-photography items you should be sure to pack:

1. Know the way back to the car! I highly recommend a GPS for this, as it can be useful in tagging your tripod as well, in case you want to leave and come back later. A compass and topo map will help in more remote areas as well.
2. Headlamp. It’s going to get dark, and you better have a light, and probably some extra batteries.
3. Warm clothes. As the night sets in it can get chilly very fast! Bring a warm jacket, hat, and gloves if it’s that time of year.
4. Food and water. If you’re headed out for a 3 hour exposure, you’ll want something to drink and nibble on.
5. Something to do. Often I am content to just sit there and stare at the heavens, but you might want a book or some music to pass the time.
6. A pad to sit on. The ground gets cold, and you’ll likely be wanting to take a seat, bringing a foam pad to sit or lie down on will make you much more comfortable. Maybe consider bringing a sleeping bag and settling in for a few hours while your camera is taking the picture.

The photography equipment:

1. Your camera
2. A programmable remote (for canon the TC-80N3)
3. Bubble level
4. Compass and declination (found on topo maps of the area)
5. Sturdy Tripod, perhaps something to weight it down
6. Rocket blower (this can be helpful if dew starts to settle on the lens, blow on it with the rocket blower occasionally and this will reduce the effect)
7. Lens hood (again, for dew protection)
8. Extra batteries (or external power source, a camera grip with the extra battery would be a good idea if you’ve got one)
9. Another way to fight condensation on the lens, is to use an elastic to affix some "glove warmers" (such as http://www.safetycentral.com/hot2hanwar.html) around the lens. Thank you Jeremy for the idea.

floris
Registered: May 11, 2006
Total Posts: 4674
Country: United States

Collecting Starlight – the Exposure:

There are a lot of variables here, and I suggest you try a few things before you settle on something.

Essentially there are two values that set the exposure: iso rating and aperture. The shutter speed will primarily determine how long your star trails are, and if you do have a foreground in the frame, it will of course affect the exposure of that. For different cameras you may find different results, but I have found that for dark (moonless) nights, iso 400 and f/5.6 seem to be ideal for most applications.

If the moon is in the sky, the exposure can dramatically change, and your foreground will be getting a lot more light. In this case the exposure time will be important.
For a full moon night iso 400 f/5.6 and 5 minutes should still be in roughly the right range.

One of the biggest let downs of many star trails images I have seen (second to the lack of an interesting composition) is that the trails are simply not long enough. The stars either need to be frozen, or they need to be long enough to compliment the composition, otherwise the sky just looks messy. The longer the lens, the shorter your exposure needs to be because the relative motion of the star is faster. Also, the length of the trails depends on the distance from Polaris – Polaris hardly moves at all, the same goes for nearby stars. Through personal experience I have found that for ultra wide angles, 15-20mm (on a full frame SLR), and including the full circle around Polaris, you need a minimum of about 2-3 hours to get a successful image, the longer the better.

The Light – It’s all about timing:

While the stars are brightest in the middle of the night with no moon, the rest of the landscape, including the sky, looks a lot better when there’s still some light out so you can see (and photograph) it. I’ve found that by starting the exposure during twilight, when there is still some glow from the recently set sun results in a nice deep blue sky and just enough light on the foreground, depending on what you’re shooting. Of course bright foregrounds will be easier to expose for. As I explain later, my preferred exposure is iso 400, f/5.6, 5 minutes, and I then take a sequence of 20-30 exposures and layer them in photoshop. As soon as that setting results in no blown highlights I start collecting light.

”Geometry of Motion” ~ Badwater Salt Flats, Death Valley National Park
The Tech: Canon 5D, Sigma 15mm f/2.8 fisheye (with some distortion correction)
Exposure: iso 400, f/5.6, 32x 5 min exposures blended, started at twilight

Alternatively you can time your exposure such that at some point the moon casts light on the foreground, but the more moon, the less stars. Another option is to use ‘lightpainting’ – use a flashlight (or flash) to light up the foreground during the exposure. Getting this right takes practice, but you can get some neat effects. For a natural look I recommend using an LED light, as the blueish white balance works better with the night sky in many cases (of course, it depends on your sky).

”Essence of Time” ~ Bristlecone National Forest
The Tech: Canon 5D, 17-40mm, LED headlamp
Exposure: iso 400, f/5.6, about 25x 5 min exposures, started at twilight
Lightpainting: In the last exposure I used iso 800 and used my headlamp to paint the tree from the side.

It would also be good to note that air traffic is least in the early morning (1-3 am or so), so if you’re having trouble with planes, that might become a factor.

Setting up the shot:

So if you’re following my advice, you’re setting up your shot while it’s still light out, but you can’t see the stars then! Of course, if it’s dark and you can see the stars, then you can’t see the land very well, so getting a nice composition will be hard. The hardest ones to set up are those that including the north star, Polaris, in the frame. Often compositions work best with it in the middle, and of course not too high up in the picture you so get complete circles around Polaris.

So how do you get Polaris in the right spot? That’s where your compass and map come into play. You need to point your camera to true north. The compass, however, points to magnetic north, which lies in Northern Canada near Ellesmere Island. The declination, found on your topo map, will tell you the difference in angle between true north and magnetic north. Using this and your compass you can find true north, now point your camera that way, and find yourself a nice composition (before it’s dark). Now, as soon as the stars start to twinkle you’ve got to work fast. You want to double-check your composition before committing 3 hours to it. So shoot a test shot of ~ 5 minutes (depending on the focal length), just long enough so you can see some rotation. This will help you find the north star, and just to double check it’s position, hopefully you’re not far off. It can be useful to note that if you can find the big dipper, the two stars marking the end of the dipper point to Polaris, and the last two stars in the little dipper’s handle point to it as well.

floris
Registered: May 11, 2006
Total Posts: 4674
Country: United States

Shooting the Twilight:

For twilight images I like to take an exposure during the last glow of pink in the sky, and then come back an hour later when the stars are out in full force. Then I will take another exposure. Then after returning home I’ll put the two images in a stack in photoshop, and use a lighten blend mode to bring out the stars. There’s a lot more details on this later on in the article.

To make the stars appear bigger in the frame, you can have them slightly out of focus, this will make them appear larger, and a little fuzzy, as seen below.

”Twilight Blues” ~ Mt. Rainier National Park, WA
The Tech: Canon 5D, 17-40mm
Exposure: 4 exposure blend:
1. (for the foreground) iso 400, f/11, 2 minutes
2. (for the mountain) iso 400, f/11, 2 minutes, shifted focus from the foreground exposure
3. (for the sky) iso 400, f/11, 25 sec
4. (for the stars) iso 1600, f/4, 15 sec, shot 1 hour after the previous three
Processing: first 3 layers blended normally, last layer in 'lighten mode'. Due to the poor quality of the stars, I went in and manually retouched the stars with a paintbrush to make them look pretty... now with a 16-35mm f/2.8 and 5DII hopefully I'll be able to get some better quality stars to start with

Taking the Picture – Star Trail Techniques:

With film you could simply flip up the mirror, go to bed, and come back a few hours later and you’d have yourself a photo (after making sure of the sunrise/sunset, moonrise/moonset, and picking a clear moonless night of course). With digital, there are some more hoops to jump through. So why use digital at all? With film there were problems with reciprocity, meaning the films sensitivity to various kinds of light changes with longer exposures, and it can be hard to predict unless you know your film well. But for really long exposures, it might make your life a lot easier. I like the control of digital, and while I have considered trying some film for these applications, I must admit that having grown up with digital, I’m no film user. Fortunately those hoops we have to jump through with digital are not insurmountable.

Noise is the number one enemy you will face. Once you start to push your exposure beyond a few minutes, the noise starts to increase significantly – long exposure noise. Also, different parts of the camera will heat up and affect how the sensor works. Most (if not all) cameras will exhibit some kind of magenta colored bloom in a consistent spot (different for different cameras). There are a number of solutions to consider.

As the temperature drops, the signal to noise ratio gets better, and your noise will decrease. So if it’s -15 degrees F outside, you might very well get away with a 2-hour straight exposure without much noise! But often times it’s not that cold (thankfully!). So for those nights you have two other options: long exposure noise reduction (available in most cameras, or it can be done manually using dark frames), or taking multiple exposures and stacking them. I have not found the long exposure noise reduction to be very effective at all, so I use multi-exposure stacking.

Shooting Multiple Exposures:

The idea here is to sequentially shoot lots of shorter exposures; the length of each individual exposure will depend on the tradeoff between noise and processing time/power required to assemble your final image. I find 5 minutes to be a nice number (so for a 2-hour exposure you’ll need 24 exposures). Note that for most cameras anything beyond 30 seconds needs to be done through the ‘bulb’ command. If you plan on trying this, I recommend getting a remote for you camera that lets you program such commands so you don’t have to manually sit there and hit the shutter (for Canon that would be the TC-80N3). For the TC-80N3 you’ll need to set the time between exposures to 1 second (it doesn’t shoot multiple exposures if you leave it at zero).

Note: turn off long exposure noise reduction, and mirror lock up. You want as seamless a series of images as you can get for star trails.

Power Constraints:

I should note here that batteries don’t last forever. Your battery might only last you for an hour, or two at the most. Using a battery grip or external power supply like from http://www.digitalcamerabattery.com/, might be a good idea. Otherwise you have to be really quick with replacing a dead one! Cold temperatures will reduce their efficiency as well.

floris
Registered: May 11, 2006
Total Posts: 4674
Country: United States

A Note on Raw Processing

When processing your raw files be sure to have the settings the same for each file. In particular, choose a white balance setting that makes the twilight exposure(s) look right, then use that same setting for all your conversions. If you're shooting jpeg, you should probably select a manual white balance in camera so that they all end up the same.

Processing and Stacking Multiple Exposures:

So, now you have a set of 20-30 exposures, but you need to assemble them into one image. This is where things get complicated, and attention to detail is important if you’re interested in the highest quality. The simplest method is to open all your files in photoshop and stack them in ‘lighten’ blend mode. There’s an easy way to do this if you have CS3 or higher:

1. Process your raw files (or jpegs), and save them to a folder
2. Open Photoshop
3. Navigate to File-]Scripts-]Load files into stack…
4. Select the files you wish to merge, and select ‘Create smart object after loading layers’
5. Then go to layers-]smart objects-]stack mode-]maximum
6. (to get rid of the smart object and get a regular layer you can flatten the final image)

Essentially, for each pixel in the image, photoshop will choose the brightest pixel of all the layers in the stack. Since the stars are the only things changing (usually), this will simple draw out your star trails. But now, if you zoom in to 100% you will see gaps, like this:

32x 5 minute exposures taken at iso 400, f/5.6, with the Canon 5D and Sigma 15mm f/2.8 fisheye lens, stacked using lighten blend mode.

After you resize to a normal web size (800 or so pixels in the longest dimension) you won’t really notice them, but in a nice print you will. You could sit there and use the clone tool to fix every gap, but if you have 25 exposures and 100 bright stars, that’s already 2,500 clone fixes – not something you want to do. There is one other possibility that sometimes works (only if you shot the circular pattern of the stars rotating around Polaris):

1. Duplicate your flattened image
2. On the duplicate image, select the entire image with the crop tool
3. Move the center of the crop box (there is a little cross hairs) to the center of rotation of your star trails. Choose this very carefully
4. Move your mouse to one of the corners, and rotate the image just a little.
5. Select this image, and paste it on top of the original
6. Set the blend mode to ‘lighten’
7. Crop a little, or use the clone tool or layer masks to get rid of the white edges in the corners

This only works if there is hardly any distortion in the picture, which doesn’t really happen with wide angles. It’s also really hard to get the center of rotation just right.

Naively you might think that those gaps are there because of the slight break in time between exposures. For a long lens you might be right, but for an ultra wide angle, 1 second is insignificant. The gaps are there because of the blend mode, by using the ‘screen’ blend mode the gaps disappear! But, then the sky becomes much too bright, so the key is to use a clever combination of the two.

Lighten Screen Blending (LSB) – Advanced Multi-exposure blending:

This method overcomes many of the shortcomings of just using ‘lighten’ layers. It works best if you shoot raw. First, lower the exposure by 1-stop (alternatively you can do this in photoshop after you’re done). When doing your raw conversion use a ‘linear’ conversion. That means you will do no curves, levels, or contrast adjustments in your RAW conversion (for ACR set all the values except white balance and saturation/vibrance to zero, make sure to set the tone curve to linear as well). Otherwise you will be affecting each end of the star trail, making the gaps more pronounced. Save the files as Tiff or psd in a new folder.

Load your files into a stack (using file-]scripts-]load files into stack), but do NOT convert them to a smart object. Now you’re going to perform a little algorithm, alternating the use of screen and lighten layers strategically to get rid of those little gaps.

Now suppose you have the following layers:

layer-1, layer-2, layer-3, layer-4

You want to duplicate each layer, except for the first and last:

layer-1, layer-2-copy, layer-2, layer-3-copy, layer-3, layer-4

Now set layer-1 to blend mode ‘screen’, select it and layer-2-copy, and merge them (select both and hit command e, or go to layers->merge layers). This is why we reduced the exposure earlier, because now you’re essentially adding exposures. Set this new layer to ‘lighten’ blend mode.

Now do the same for each successive pair, so set layer 2 to blend mode screen, and merge it with layer 3-copy, then set the new layer to lighten.

After doing this for all your layers you will end up with a stack of layers all set to ‘lighten’ blend mode, and by strategically using the screen blend mode we have made sure each gap is filled in.

Now flatten the image and go ahead and do your normal processing. The result? Here you go..

Same files as before, processed at -1 exposure in raw, and blended using the LSB method. No further adjustments. I don't really understand the other gaps and weird star lines, they're long than a single exposure, some I'm not sure what's happening.. The two gaps per trail you do see are when I had to replace my battery.. I need to go in and fix those all, oh boy!

If you could have a low noise 2-3 hour exposure (ie. on a very cold night, or some time in the future with better cameras), you’d be better off doing that, why waste your time processing?

A note on dark frames:

If you want to get into astrophotography, I recommend you do some more research, and read a book. There are many techniques that are much better for getting detailed images of stars (not star trails), including the use of dark frames. I have not found dark frames to be useful with my cameras and techniques, but you might find them useful – I recommend you do a search on google.

floris
Registered: May 11, 2006
Total Posts: 4674
Country: United States

Summary:

1. Plan and prepare: consider location, time of year, sunrise/sunset, moonrise/moonset, moon phase, etc. and how each of these might affect your proposed image.
Before you head out the door: have a safe way back to the car, be prepared for spending some time alone, in the cold and dark. Bring a headlamp, GPS, warm clothes, food and water.
2. Compose your shot early: don’t wait until the stars are out, you’ll miss the best light. Bring a compass to help you find the north star.
3. Exposure: I recommend trying multiple exposures, each of iso 400, f/5.6, 5 minutes. Use a programmable remote to make your life easy. Remember: it’s not just the star trails you’re exposing for, but also the foreground and sky. I recommend starting soon after the first stars start to appear, and use a moonless night unless you want to lighten up the foreground more (in that case shoot around moonrise/set).
4. Multiple Exposure Technique: Use a programmable remote (for canon the TC-80N3), set your time between exposure to the minimum (1 second), and turn off long exposure noise reduction and do not use mirror lock up.
4. Power constraints: most batteries don’t last as long as you might want to shoot for. Depending on the temperature your battery might only last about an hour. Use a battery grip or external supply to make your life easy, or be really quick in replacing a dead battery!
5. Processing: For an easy solution stack everything in ‘lighten’ blend mode. For high quality results, use the algorithm described above.

Spool
Registered: Apr 25, 2006
Total Posts: 39
Country: Australia

wow what a great in depth tutorial, thanks so much. going to put it into practice this weekend.

cheers

Daniel K
Registered: Feb 07, 2007
Total Posts: 541
Country: United States

What is your interval between shots? I did 15 min exposures with 20 second intervals and had small but noticeable gaps in my trails. I did the intervals shorter than what was recommended to me to allow time for the sensor to cool down. Does anyone know how long the sensor retains heat? I use a mark 3.

hugh
Registered: Jan 09, 2002
Total Posts: 29225
Country: United States

Hello Floris,

Thanks for all the hard work and attention to detail and for sharing it here.

hugh

doigal
Registered: Dec 20, 2004
Total Posts: 192
Country: Germany

I'm reasonably sure someone has scripted or put the steps you described into an action for photoshop to chew through without you having to do all that work (might be helpful if you have 200+ 30sec shots!)

Either way, great tute!

Dneufarth
Registered: May 31, 2008
Total Posts: 1003
Country: United States

An excellent tutorial with excellent images, thanks so much for sharing, Derek

jforkner
Registered: Dec 02, 2008
Total Posts: 260
Country: United States

Thanks for the great insight. Lovely pics, BTW.

Jack

aFeinberg
Registered: Mar 15, 2006
Total Posts: 3780
Country: United States

holy ^@#$ what nuts pics. much love floris

aF

free2run
Registered: Jan 14, 2005
Total Posts: 102
Country: United States

Very nice and detailed article and outstanding shots.
Thank you so much for sharing your experience with us, floris. I'll definitely try it.
Wei

Ray Still
Registered: Oct 10, 2008
Total Posts: 8050
Country: United States

Great Tutorial these will definitely be put to use by me
Thanks for spending the time to share

Ray Still

Chaz
Registered: Mar 20, 2004
Total Posts: 916
Country: United States

BRAVO! Clap-Clap-Clap!! An extremely well-written tutorial that I will want to use in the field. Thanks for the selfless, time-consuming effort and the beautiful photos illustrating the technique.

thw2
Registered: Dec 27, 2004
Total Posts: 1954
Country: N/A

Chaz wrote:
BRAVO! Clap-Clap-Clap!! An extremely well-written tutorial that I will want to use in the field. Thanks for the selfless, time-consuming effort and the beautiful photos illustrating the technique.

+1

Really appreciate this. Perhaps this can be turned into a sticky?

dcad10
Registered: Aug 26, 2008
Total Posts: 292
Country: United States

this is excellent, I've been looking for something just like this to help me get started shooting my own star trails.

realkuhl
Registered: Apr 22, 2003
Total Posts: 6808
Country: United States

Awesome photos and excellent information to back them up!! Love the DV shots a lot....really well done!

Chetan Kulkarn
Registered: Mar 12, 2006
Total Posts: 85
Country: India

thw2 wrote:
Chaz wrote:
BRAVO! Clap-Clap-Clap!! An extremely well-written tutorial that I will want to use in the field. Thanks for the selfless, time-consuming effort and the beautiful photos illustrating the technique.

+1

Really appreciate this. Perhaps this can be turned into a sticky?

+2

The effort to put this all together is truly appreciated. And the images are excllent.

Thank you very much.

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