How to: Photograph Star Trails

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By Trevor Williams - http://diyphotography.net

What Will You Need?
Before you gas up the car and head out in to the night, check the short list below to make sure you have all the required gear.

A camera capable of shooting in “Bulb” mode
A sturdy tripod
A cable release
Some things that you will find useful but are not necessary to get started would be

A decent flashlight,
Some extra warm clothing and
Anything else to prepare you for the weather and elements.
If you are heading into a remote location it may be much colder at night than what you are used to where you live. So be prepared.

Where should I go?
I tend to look for locations that are have some foreground interest. It may be an abandoned building, large infrastructure like a radio tower or a bridge, or some natural features like rock formations or big trees.

You may choose to add light to these features with a flashlight or keep them as silhouettes against the star filled sky.

Though it is possible to capture star trails in town, it is much easier if you try this far away from any city lights. Darker skies means you can crank up your ISO and open up your lens really wide and capture a greater number of visible stars.

City lights that are not even visible to the naked eye will show up over a long exposure so when you think you have finally found some dark skies keep on driving!

It really pays off doing some research before embarking on a shoot especially if you have never seen the location in the day before.

Star Trail Basics
There are multiple ways to go about shooting star trails. I will start with the basics that do not change whether you are using an analogue SLR or a DSLR.

Before dialing in any settings you should go ahead and mount your camera onto a tripod. Roughly compose your shot and set the focus.

Focusing
In the dark, it is not easy to get the AF to lock on to anything, but do not worry there are several solutions to this.

If you are including foreground objects I suggest making sure that they are in focus. If you are using a wide angle lens the foreground object and the stars will probably both be in focus even at a very wide aperture. I find that it is fairly safe to just set the focus to infinity if it is a wide angle or fisheye lens right from the start.
Some lenses will not have those markings so shining the light on the foreground subject while using the AF function may work if the flashlight is bright. If not go lay the flashlight on the ground at the base of what you are shooting and focus on that.
Once you have achieved the glorious state of "in focus" be sure to set it to MF or manual focus before starting your exposure or it will start searching again when you start the exposure and you will lose your focus.

Composition
So now you should have your camera focused and set to manual focus (MF) and the shot roughly composed.

When composing the shot try not to include any direct light sources, like streetlights, in the shot.
If you are not using film then I suggest doing a test shot which aids in composing your final shot. A test shot can be made by doing a 2-3 minute exposure at very high ISO and wide aperture. This should be enough to be able to see which direction the stars are moving and allow one to imagine what the final shot will look like.
Recompose the shot if necessary and zoom in on the LCD to double check you focus is accurate.

White balance
White balance is the relative warmth or coolness of white light. A white object would appear slightly blue with a cold color temperature and it would look slightly orange with a warm color temperature. I tend to shoot night skies with the white balance set to “tungsten” which gives a nice blue look or the extreme opposite of 10000 Kelvin giving it a deep orange color. I find that auto white balance leaves the sky brownish or "dirty" looking. You will have to refer to your cameras manual if you do not know how to change these settings.

White balance setting will affect the whole image so if you have included some foreground objects, you will need to consider what you are using to light them with. I use a variety of flashlights for this job and my white balance settings help me to determine which one to use.
LED light is very blue so if you are shooting with your white balance set to tungsten the objects lit with that light may look unnaturally blue. To avoid this I use a xenon flashlight or flashlight with an incandescent bulb which have a much higher color temperature and neutralize the blue effect. A warm light leaves objects lit with them with a natural or true color.
If LED is your only choice then consider putting some orange cellophane over the front to alter the shade of the light but doing this will reduce it effective power.
If I am shooting with my white balance set to 10000K I would generally use an LED which is the exact opposite of the above situation. Its bluish hue would neutralize the high color temperature of 10000K leaving the objects lit with it a natural or true color.
So for a cool white balance use a warm light and for a warm white balance use a cool light for lighting your foreground interest.

Single Shot Vs. Stacking
For shooting options, one could choose to do it all in one shot or shoot multiple shots and “stack” them after the fact using computer software. I personally find that shooting multiple images and stacking them yields much nicer images than those done all in one shot.

Single Shot
If you are going to do it all in one shot then your biggest concern should be noise. To fight noise, one could use a narrower aperture and a lower ISO speed but these settings will typically not pick up very many stars. If this is the route you are going to take, and I suggest at least trying it, then here are the steps and settings to follow:

Focus and compose the shot.
Set the time value to “bulb”
Set the aperture to its widest
Set the ISO at 200
try for a 30-minute exposure with a wide aperture of 3.5 - 4.0.
If there is too much noise then drop the ISO to 100 and either shorten the exposure time or try a narrower aperture.
If shooting this way is your only option, there is something that you can do to increase the appearance of the length of the trails in the frame. (remember, those will be limited to due to the short exposure time). The actual length (or appearance of length) of the trails is determined by two factors: Exposure time and the focal length you are shooting at.

For example, stars over a 30-minute exposure would appear much longer in the frame at 50mm than they would at 15mm. If you find that you are limited to shorter exposure time due to noise, or any other factor, try shooting at a longer focal length to increase the appearance of the star trail length in relation to the frame.

Stacking
My heavily preferred way of shooting is shooting multiple shots and "stacking" them later using computer software. Shooting short exposure pictures means less noise, so one can shoot with a wide aperture and a faster ISO that will pick up many more stars than the previous method.

One can do this because noise becomes much less of a factor. Noise generally increases with time and with stacking, you only have to worry about 30 seconds. That means even at ISO 800 noise will be less of an issue to worry about.

There is even an option to include dark frames, which are frames shot with the lens cap on, so that even the tiny bit of noise from ISO 800 over 30 seconds will be removed.

With the higher end DSLR’s and the improvement of sensor noise reduction in newer DSLRs the ISO can be bumped even higher which will result in even more visible stars streaking across the sky. Of course, you will need to find the balance for your camera based on how it handles noise.

For the stacking method it is necessary to use a cable release. It could be done with a remote but then I would recommend shooting much longer exposures than 30 seconds and stacking those, simply because a remote is not as comfortable to use.

You will be shooting possibly hundreds of images so it is important to make sure there is plenty of space on your memory card.

To get started, set your focus and compose your shot.
Set the aperture to its widest and the ISO to 800 for starters.
Dial in 30 seconds for the time value and the drive mode to “continuous shooting” mode which allows for non-stop shooting when the cable release is locked. (Now you get the cable release thing, right?)
I suggest doing a test shot first to see if everything looks all right before locking that release. If anything is too bright then dial the ISO down. Once you have taken the shots you will need to stack them using software. (More on that in a bit)

What do you mean by "Lighting A Foreground Interest"?
I mentioned above about adding light to the foreground objects and explained a few things to consider about white balance in relation to that. I often include foreground objects to complete the shots because images of just stars sometimes seem to lack a subject (and interest).

I look for interesting buildings, infrastructure or natural objects like big trees or rock formations and make them the subject of the images. I light these foreground subjects with a flashlight or speedlite. A flashlight can reach far places and can be moved around while lighting to remove shadows while a speedlite can freeze a tree that may be moving in the wind.

You will probably use a flashlight most of the time because they are a much more flexible tool and leave the foreground with a much more organic look. I highly recommend doing a few lighting test shots to see how much light is needed before locking that cable release. Too much light will distract from that beautiful star filled sky you are about to create. Remember, for foreground lighting: if you are shooting at low whilte balance, use a "warm" light like Xenon torch; if you are shooting at “tungsten” white balance, use a "cool" light like LEDs flash light..

If you are stacking then I suggest doing the foreground lighting at the beginning and again at the end. In case one of those is unsuitable for the final shot. You simply exclude those frames from the stack. If it was done in the middle and a mistake was made leaving those frames unusable it would create a break in the trail that would take away from the shot.

A final note for those with experience in night photography, keep in mind that you are now shooting wide open with your ISO jacked so adjust your lighting techniques to accommodate for that with low power flashes or less lighting time with a flashlight.

Stacking software (all free)

StarStaX
This is my favorite software. Unlike other free programs, it runs on Mac and Linux as well as Windows. What I like about StarStaX is the incredible speed. It is waaaay faster than using Photoshop and much easier as it does not require you to create any blank documents to get started. Open up the program and import your images. Hit start and within seconds your image is finished. Check out the homepage to see the great features it has.

Photoshop Stacking action
This method gets the job done but is slow and ties up memory while stacking.

Startrail.exe
One major downfall of this software is that is only available for Windows. I used this a long time ago before I started using Mac. This got the job done and before StarStaX was a way of creating animated time lapse video of the stacks. I think this software has now become old and needs to be revamped if its author wants people to continue to use it.