Digital Classroom:

Welcome to the first of a new series of blog posts titled “Digital Classroom”. This on going series will focus on different aspects of photography; from learning about depth of field to understanding what is possible with todays technology. For the first article, we will focus our attention to shooting “star trails”, mostly because this is the most asked about subject after my last trip to Wyoming. I hope you enjoy!

How do you shoot star trails?

Intro

When looking up at the sky on a clear night, sometimes we are able to get a sense of just how vast the universe really is. If you are fortunate enough to be far away from a populated area then you will be dazzled with billions upon billions of these tiny reflecting gas giants. As a photographer, one can’t help but get excited at the notion of how much beauty one can find in a night sky, however most people feel daunted when it comes trying to capture that beauty.

With a simple search of Google Images or Flickr you can find hundreds of thousands of photos of the night sky.  Every once in a while you will come across an image that was executed so perfectly, that you almost feel as if you were there. You might ask yourself, how did they do that? How do they compose that image in the dark. Where would I set my focus on? How do you light up a tent correctly during a long exposure? Lets see if we can answer a few of these questions…

What do you need?

Required:

• Camera (Digital or Film) that is capable of manually controlling exposure.
• A Tripod
• Digital Memory Cards (or Film of ISO 400 or greater)
• Flashlight
• Patience

Optional:

• Warm Clothes
• Wired or Wireless programable remote (Such as THIS)
• Hot Chocolate (Thank my girlfriend for adding this)
• Pack of cards (or anything to help pass the time)

Possible Problems:

• When shooting the night sky, there are a handful of things you need to keep in mind. First and foremost is to dress appropriately. The best star trails that I have shot have always been when I was off in some remote mountain area, far away from civilization. With high altitude comes colder temperatures and there is nothing worse then waiting an hour for an image to expose while freezing.
• “Hot Pixels” – These are individual pixels which look much brighter than they should, almost looking like stars. These pixels occur because of electric charges leaking into your digital cameras sensor wells. These excess charges increase the voltage to the well ( or pixel) which in turn makes the pixel look “hot” or “bright”. When we shoot long exposures, the digital sensors in our cameras run hot, making “hot pixels” much more prevalent and obvious when the image reaches your computer screen. Because this issue has to do with DIGITAL SENSORS, people who shoot in film don’t have to worry about “Hot Pixels”. It is still argued to this day that shooting long exposures with film cameras is the only way to go, but I will show you how to fix this digital problem (depending on the features of your digital camera).
• Batteries – One of the downsides of digital cameras when compared to film cameras is how power hungry they can be. While the professional level cameras have batteries that last for an incredible amount of time, the entry level DSLRs are not nearly as good. Always carry a few extra batteries when venturing away from a power source for a long period of time. It is never fun to be in an amazing location and loose power. It is also good to know that batteries dramatically loose power in colder weather. If you set a battery out in the cold and leave it there for a few hours, it will drain incredibly fast, or at least appear to. If you try to put a battery in your camera that is freezing, it might show that it is very low or might not even power on at all, even though you haven’t used it yet. There is however an easy solution. Keep your batteries warm by keeping them in your pockets and sleeping with them in your sleeping bag at night. If they are already cold, then warm them up with your hands, utilizing your body heat. You will be surprised at just how much battery life you can squeeze out of a cold battery if you get it warm again.
• Ambient light – Light from cities (otherwise known as light pollution) and light given off from the moon can severally effect how many stars you see at your location. I will touch on this further on.
• Planes, Trains and Automobiles – Ok, well maybe not trains and automobiles, but I did love that movie back in the day. When you are shooting a long exposure, your camera’s sensor is picking up any and all light. That means passing airplanes and satellites can very well be your enemy. After setting up to shoot the image below, my girlfriend and I laid down on the ground with a blanket and stared at the stars to pass the time. I distinctly remember watching an approaching plane, knowing full well that it was going to be cutting across my image. If you look closely at the Southern Teton (the peak on the far left in the image below) you can see the faint line of that plane. Got to love commercial jets messing up your shot right?
• Patience – You will need a lot of patience when it comes to capturing star trails which is why I listed it as a requirement.  It takes time to set up, compose, run test shoots and then wait for your final image to expose. If you try to rush it, I promise you that you won’t be happy with the result. Take your time, this is not an exact science.

Light:

Light is the essence of photography. Using the “John Muir” ad on the left as an example, I knew that although moon was going to be present that night, that it wouldn’t rise until around 3AM (got to love the internet). Knowing the stage of the moon, its location in the sky and when it will be present is very important. Just as “light pollution” (excess light from cities) can block out the light reflected from stars, the moon can be just as damaging to an image. However you can use it to your advantage, such as in this image from Arches National Park of Balanced Rock..

As you can see, I wasn’t able to get nearly the same amount of stars as I was able to get in my ad, even though both images had similar exposure times. I was still able to create a unique image because the light from the moon lit up a portion of Balanced Rock while still allowing some star trails to get caught in the background. While very different, this image is still dramatic, just in its own way.

Within the context of light is the choice to make when it comes to your ISO, or digital “film speed”. Changing your ISO determines how sensitive your camera’s sensor is to light with a low ISO (ISO 100) being less sensitive than a high ISO (ISO 64000) which would be incredibly sensitive. While low ISOs generally create the cleanest images they require more time to expose an image. While high ISO’s give you shorter exposure times to capture the same amount of light, the light sensor picks up excess noise (remember “Hot Pixels”) because the camera amplifies the electronic signal, causing distortion, which becomes visible in the form of little specs (noise). I currently use Canon’s 5D Mark II and 1D Mark III for the bulk of my photography work. Both of these cameras can produce very clean images beyond an ISO of 1600, but that doesn’t mean that I would make my camera that sensitive. Most amateur DSLR cameras can easily handle an ISO of 400, which is what I recommend using for most night time images.

Aperture:

Although a significant part of the equation that is an exposure, the aperture is probably the least important aspect of creating a stunning night image. That doesn’t mean that it is not important however. Some photographers will tell you that you should shoot with the lowest aperture that you can, typically around F/2.8 (to allow the most light in), but if you haven’t figured it out by now, I am the type that would rather do it right and wait longer for an exposure.  When shooting lower than F/2.8 or near F/40 (two ends of the extremes) physics comes into play. Aperture by definition is the control of “depth of field”, or blurred background known as “bokeh”. The lower the aperture, the more blurring the background becomes and the higher the aperture, the more in-focus it becomes. However, there is always a trade off. On either side of the spectrum, you are loosing overall clarity and sharpness in an effort to control depth of field. I usually follow the landscape guideline of aperture, shooting somewhere between f/8.0 and f/11. This range, for the most part, gives you the most sharpness and detail throughout the image, something that is very important if you are considering light painting (i.e – lighting up a tent).

Exposure Time:

Probably most important aspect to capturing star trails is how long you leave your shutter open. Most DSLR cameras will allow you to adjust your shutter speed up to 30 seconds. Beyond that, you have to change to the “Bulb” setting. Setting your camera on “Bulb” mode, gives you the freedom to hold the shutter open for as long as want, which is where a wireless or wired remote comes in handy. If you don’t have one of these, you are stuck with holding the shutter button down for as long as you want to expose your image. Try holding the shutter button down for just 2 minutes, then image doing it for 27. You get the idea. Once you have one of these remotes, it is just a matter of determining how long to leave the shutter open. For our example, I determined that an exposure of 27 minutes would give me that kind of star trails that I wanted. The longer the exposure, the greater the “vortex” of stars, but the more chance you have of a satellite or plane crossing your section of space.

Because this is not an exact science, there is no formula I can give you that will help you determine how long you should keep your shutter open. In the end it is a game of guess and check.

Composition:

On my recent trip to Wyoming, I knew that a silhouette of the Tetons or of Titcomb Basin in the Wind River Range would create an amazing foreground to the night sky. I went to these locations with the intent of shooting star trails against these amazing mountains. While alot of amazing things can happen organically when it comes to capturing amazing moments in life, it is always good to be prepared and come to a location with an idea, even if you know that that idea will always change in some form or another.

Lets look at the first image in this blog as our example, my new ad featuring words by “John Muir”. When choosing my initial campsite, I was already attempting to visualize the composition of the star trails image I wanted to shoot that night. I knew the slight hillside that lead up to the mountain ridge would give me enough room to utilize the space for an ad. I knew that if I composed my tent in the lower left side of the photo, that I would be able to truly capture the circular pattern of the stars, effectively creating a vortex within the cosmos.

Set up your tripod and determine if you are going to shoot in landscape (horizontal) or portrait (vertical) format.  I recommend then changing the ISO to 3200 and shooting a few test shots at around 2-3 minutes each. These tests will help you adjust your overall composition, keeping horizons in line and giving you an idea how how your final image will look.

Focus:

After you have composed your image in the dark….how do you know what to set your focus on. The answer to this question is simple depending on what you are shooting. If you are just planning on shooting a silhouette of some mountain peaks in the foreground and the night sky in the background, then you can switch to manual focus on your lens, use your flashlight and twist the focus ring until it reaches the infinity symbol “∞”. This tells the lens to focus on on furthers reaches of the image.

If you are planning on light painting, then it is a little more difficult. If you have a powerful flashlight and a friend, have them shine the the light on the tent (it doesn’t matter if they are in the image or not) and then hold down the shutter button half way. Hopefully the camera will autofocus to the tent. If not, you will have to manually change your focus point to an area near the tent, pick up or tilt your tripod so that that area is over the tent, and then hold down the shutter half way again. Once complete, move the tripod back to its original position and switch the focus on the lens to manual, so that the camera doesn’t try to re-adjust once you are ready to take your final image.

Light Painting:

Although obviously not required, learning how to correctly light paint will open up creative doors for images you never thought possible. With the simple application of a flashlight, you can create stunning images that stand out from the rest. Light Painting is pretty much exactly what it sounds like. By adding artificial light to illuminate an object during a long exposure, you are in effect painting with light. The problem with light painting is that everything you have done so far has an effect how just how much light you need to add to correctly exposure an object during a long exposure. The ISO you choose, the aperture you set, how long you expose your image for and even your composition plays a roll in how well the final result comes out. Again it becomes a game of guess and check. Looking back at our example, the John Muir Ad, I was able to successfully paint the tent with the help of my girlfriend. After I composed the shot and adjusted my settings I had her sit inside the tent and turn on her flash light when I told her to. I had her move across the inside of the tent in a side to side motion, covering the entire tent for 3 different passes, all of which lasted no longer then 12 seconds at a time. I came to this formula after running some initial tests at an ISO of 3200 for 5 minute exposures. When I figured out what I felt would work well, I reset the ISO to 400 and began to take my final image. Once you start taking your shot, you have to remember that any light will be captured by the camera. If you have a powerful flashlight and you don’t have someone else to help out, then be sure to find out how close you can get before you yourself are caught in the image.

Fixing “Hot Pixels”

image property of NZ Digital

Although we have already talked about what “hot pixels” are, we now have to know how to deal with them. The easiest and best way to fix hot pixels is to change a setting inside your digital camera called “Long Exposure Noise Reduction” to “On”. What this does is shoot a second image, with exactly the same settings as your original, right after the first exposure is done. The only difference is that the shutter is left down for the 2nd exposure, creating what is called a “Black Exposure” image. Even though the sensors in our cameras are all different from each other, an individual sensor will get hot in roughly the same places for a given photograph. by shooting an identical all “black” image immediately after the first one, the camera in effect is mapping out the “hot pixels” that its sensor produces at that given time. So if you shoot a 27 minute exposure, you then have to wait another 27 minutes for the 2nd “black” exposure. The camera then takes both images and compares the hot pixels in the “black exposure” with that of the original. If it finds similar hot spots, it will cancel them out, leaving you with a much cleaner image.

This process does take time and can be frustrating, but the results are well worth it. It is because of steps like this one that it is imperative that you take your time composing, testing and experimenting with your shot before you are ready for your final image, otherwise you will be wasting twice the amount of time and still not getting the results you want.

* It was also pointed out by Photographer Tony Eckersley (http://www.tonyeckersley.com/) that if you shoot in RAW format, as opposed to JPG, and you use Adobe Lightroom, that Lightroom will help clean up most if not all of the hot pixels out of your image. Thanks Tony!!!

Conclusion:

When it comes to shooting star trails, remember these pieces of advice:

• Composition is HUGE – Before the light goes out, try to get an idea of how you would like to compose your image
• Shooting star trails is not a science and you will need to run some test shots before shooting your final images
• Dress appropriately! No one likes to freeze
• Have FUN! Enjoy stepping outside of your boundaries when it comes to shooting photography. Try new things and learn from your mistakes for when it all comes together, there is nothing like looking at the final result and having it bring you back to that amazing moment, when you were staring up at the cosmos and thinking about just how beautiful the vastness of life could be.