Star Trails

Long Exposures: Part V

I’ve done many posts on things you can do with long exposures (see Disappearing Act and Long Exposures, DSLRs: Photographing Fireworks, Lightening and Long Exposure, and Long Exposures), but here in another one: Star Trails.

First, what is “a long exposure”?

When we talk about the length of exposure, we’re talking about how long the shutter is open in your camera to allow light in. Now, you may already know that how “bright” the image ends up being (or the exposure value) is dependent on the combination of shutter, aperture, and ISO settings. These 3 settings in combination control how much light reaches the sensor as well as how much light is required to get a given exposure value.

So, why would we talk about the length of the exposure separately?

How long you open the shutter determines whether you freeze motion or show motion blur and how much. So, when we talk about a long exposure, we’re really talking about showing motion in our images. Getting good exposure still requires a combination of setting the shutter, aperture, and ISO appropriately.

So, now that we’ve reviewed the basics, let’s get into a couple of examples of what you can do with long exposures (slow shutter speeds).

Star Trails

When we look at the stars, if we look at them long enough, then appear to move in the sky. This is because the earth is rotating so the stars rise and set just like our closest star, the sun. They actually move fast enough that we can record their path as a “star trail” if we leave our shutter open long enough. You can also take a series of photos and use software to combine them.

For the purpose of this blog, I’ll just tell you what I did to get this image:

Star Trails

  1. Find a location where it’s very dark and you are far from the city so you can see lots of brilliant stars in the sky.
  2. Attach remote control to camera (a remote is an absolute requirement for star trails).
  3. Place the camera on a tripod and frame what you want in the image and determine how/where you will need to focus (see next step).
  4. If you have something in the foreground on earth (like the trees in my image above), you might want to check a depth of field calculator to determine whether you need to find focus on the trees of whether you can simply focus at infinity. If you are focusing on something fairly close, you may need to use a flashlight or focus assist on your flash to find focus in the dark if you cannot see well enough to focus manually and your camera can’t see well enough with the available light to focus automatically. Just shine the flashlight on the thing you want to focus on, point your camera at that thing and lock focus (hint: this is easiest if you’re using back-button focusing, but that’s a subject for another blog post). In most cases, you will be shooting wide enough and at objects far enough away that you can simply manually set the focus at infinity and everything will look sharp. In my case, I was using a full-frame camera with a zoom lens at 27mm and my aperture at f/11. Worst case, focusing at infinity would keep everything 8 feet and further sharp. Since the trees were more than 8 ft above my head, I just set my focus at infinity.
  5. Now that you’ve found focus and locked focus, you can get your camera set on your tripod and framed the way you want again.
  6. Make sure your camera is set to “Bulb.” For some cameras, this is a setting on the shooting mode dial (where you pick Auto or Manual). For other cameras, this is an option in the shutter speed selection.
  7. Make sure your remote is set to “Bulb” as well. Bulb allows you to manually open the shutter and then manually close it.
  8. I personally like to just take a shot based on feel and then adjust from there. I started by trying to get a shot that just looked realistic. I left the shutter open about 70 seconds and this is what I got:

How the Sky Looked

  1. Because there was so little light in the area I was shooting in, I wasn’t worried about over exposing the trees with a very long exposure. If you have more ambient light, you might want to stop down more or turn down the ISO. In my case, I did f/11 for aperture and 1600 ISO. I used a higher ISO than usual because I wanted to ensure the sky registered enough light to clearly show the silhouette of the trees. Had I not been so sleepy by the time this shot completed and keeping my husband awake getting in and out of the tent to tend to the camera, I probably would have tried another shot with a lower ISO and longer exposure time to see how long I could get the star trails and if I could reduce the noise.
  2. Make sure you have a comfortable and warm place to sit where you can keep an eye on your camera. I was more worried about curious bears than people at our campsite since there wasn’t anyone else around. Also, set an alarm on your phone so you don’t forget when it’s time to close the shutter. For my example, I opened the shutter (by pressing the button on the remote 1x) and then set the timer for 30 minutes. However, I must have bumped the shutter button early because my metadata says the total exposure time was actually 1275.9 sec (21.26 minutes). The longer you leave the shutter open, the longer your star trails will be. However, be aware that extremely long exposures create more noise in the image and can build enough heat in the camera that it will shut itself off (hopefully) to avoid damage. At one time I recall reading a warning that there is a maximum limit to how long you can safely leave your shutter open on a digital camera, but I have not seen anything like that in years so this may be something only relevant for older DSLRs (or perhaps it was just a rumor).
  3. When your timer goes off, click the button again to close the shutter and go see what you got!

Trivia question: why do the star trails appear in a semi-circular pattern?

 

 

 

I used both the Noiseware and Nik Color Efex Pro plug-ins with some minimal post-processing adjustments in Aperture no this one to try to pull out the 3 dimensions of the clouds as well as eliminate noise.  Not quite happy with it, but the lightening strike was amazing.  16mm (cropped), 9.8 seconds, f/16, ISO 200

Lesson 109 (DSLRs): Lightening and Long Exposure

Since I promised more examples of things you can do with long exposures in Lesson 108 and then we had a storm that offered a great opportunity to shoot lightening, here’s the first follow-up example.

Before we go into how to shoot lightening, let’s start with a little background on the shutter setting I prefer for this.

For lightening shots, I think it’s easiest to use that mysterious shutter speed called “Bulb.”   The first step is to find how to turn it on.  In some cameras, the shooting mode dial on the top of the camera has a “B” for Bulb and turning the dial to B is all you need to do.  In other cameras, “bulb” is at the end of the shutter speed options just past the setting for 30 seconds.  In this case, turn the shooting mode dial to “M” (for Manual) and then set the shutter speed to “Bulb.”

So now you’re in “Bulb” and you may be wondering what the heck that means.  This setting let’s you to open the shutter and keep it open until you decide to close it.  To do this, you either have to hold the shutter button down the entire time you want the shutter opened or you need to use a remote.

I am currently using a Pixel Pro Oppilas wireless remote, which was amazingly cheap.  In fact, I accidentally ordered 2 and decided for the $20 price tag, it was worth keeping the second one as a backup.

In any case, whether you choose a cheap 3rd party wireless remote, a wired remote, or a high-end wireless remote, you will definitely want a remote for bulb exposures.  There are two reasons for this:  1)  It’s very annoying to have to stand around holding the shutter button down for extensive periods of time, and 2) It’s extremely difficult to hold the shutter button down without introducing camera shake, which will cause blur in your images.

So, you’re in bulb mode and you have a remote attached to your camera.  You will also need to put your camera on a tripod.  This is a must.  And a solid tripod that won’t allow your camera to vibrate helps tremendously.  Alternatively, you need a really solid place to set your camera.  A fellow photographer friend says setting the camera on a large bean bag will help keep it stable if you have a flat surface to put it on.

Next, you need a safe vantage point to shoot from.  A safe vantage point is not, for example, the middle of an open field, under the one tree in said open field, on a roof top, or anywhere above timberline on a mountain.  A safe vantage point generally means that you are indoors.  Some folks shoot lightening through car or home windows using a polarizing filter to remove glare from the glass.  This is definitely the safest thing to do.  For recommendations on lightening and safety, go here:  http://www.lightningsafety.com/nlsi_pls.html

I will make no recommendations and I am not going to tell you where I shoot from because I don’t want to be responsible for anyone besides myself when it comes to lightening safety.  🙂

That said, let’s assume you’ve found a good, safe place to shoot lightening from.  Now that you’ve found your place, you next need to be there at the right time.

Since night time lightening is more dramatic, if you are at home in the evening, having a spot you can get to on a moment’s notice increases the odds that you will be able to capture some great shots.  Otherwise, watch the weather forecast and be prepared to go to your favorite location only to be disappointed.

Let’s say all has aligned and now you have your camera in Bulb, with a remote, on a tripod, in a safe location, and there is lightening!  You are 90% of the way there!

There are lots of different opinions on what to do next.  This is my personal preference:

  1. Use the widest focal length you’ve got.  It greatly increases the odds that lightening will be captured inside the frame since you cannot predict where it will strike.  The examples for this post were shot at 16mm on a camera with a full frame sensor (meaning 40% wider than if you’re using a crop-sensor camera).  Images were then cropped in post-processing.
  2. I use one of two options for focusing.  If there is enough light to focus either automatically or manually, I like to focus on an object in the landscape that will result in getting everything in the frame sharp.  I like to include foreground objects (like buildings) for scale.  If it is too dark to find focus, I set my lens to manual focus and then turn the focusing ring until the mark aligns with the infinity symbol (this is called focusing at infinity).  If everything in the frame is at the hyperfocal distance or further from the camera, this will keep everything sharp as well.  (If you don’t know what hyperfocal distance is, it just means from that point on, everything to infinity will be acceptably sharp.  You can use a Depth of Field calculator to get an estimate of this distance.  See Lesson 106 for more info on calculating this.)
  3. Stop down the aperture to something around f/16ish.  I like f/16 because it gives me so much depth of field that I don’t have to worry about everything being sharp and, more importantly, allows for very long exposure times without overexposing the image between lightening strikes.  That said, when you are shooting with a very wide angle focal length and your subject is far away, you don’t need to be on f/16 to get a lot of DOF, so feel free to try opening up the aperture if you find that works better for you.
  4. Set the ISO as low as you can.  I started with ISO 400, over exposed a strike that was very close, turned it down to 100, under exposed several strikes that were further away, and then turned it up to 200.  This is not an exact science, but be aware that long exposures, especially at night, tend to get very noisy (speckled and grainy).  Setting a high ISO will also add noise, but decreases the length of time the shutter needs to stay open.  In this case, what we’re trying to do is keep the shutter open as long as possible with the least exposure until lightening actually strikes.  So, we really want just enough light amplification (what the ISO setting controls) to allow for a great exposure during the lightening strike.
  5. Get your camera all set and pointed at the sky (don’t forget to level it) and then take a comfortable seat.
  6. Some people claim they can sense lightening before it strikes.  I suggest that if you find your arm hairs standing on end or have some sense of an electrical charge, it’s time to move–quickly!  I open the shutter with my remote and watch and listen.
  7. I leave my shutter open for a while and watch how many flashes there are in the sky and how bright they are.  If they are not very bright, I will wait through several flashes and then close the shutter (by pressing the remote shutter release a second time). 
  8. This next step is critical:  look at the exposure you got.  I do not have a scientific way to predict what exposure you will need for lightening.  This is very much a feel thing.  The longer you sit there watching the storm, guessing at how much light has reached your sensor and checking to see if you guessed right, the better you will get at this.  The important thing to bear in mind is that when lightening strikes, if it’s very bright, it’s time to close the shutter and start the next exposure.  Conversely, if you’ve been getting lots of flashes in the clouds but no bright strikes and you’ve had the shutter open for a while, it’s probably time to close the shutter and start over.  If the sky gets too exposed before the lightening strikes, the lightening will not show up as well.

One word of caution:  leaving your shutter open for extensive periods of time will drain your battery quickly.  Make sure you have a fully charged battery (and a spare if you have it).

In a nutshell, my approach to get lightening shots is to have the right equipment, show up in the right place at the right time, get ready, and then open my shutter and adjust as things happen.  Kind of like life.  🙂

The water cannons at night at Coolidge Landing in downtown Chattanooga, TN

Lesson 108 (All Cameras): Long Exposures

Note for iPhoneographers: the SlowShutter app will allow you apply this information to the iPhone, although stabilizing the iPhone (even in an iPhone tripod) can be challenging.  See Lesson 101.

When I teach beginning photography workshops, one of the things I spend a lot of time working with students on is the relationship between exposure and artistic expression.  Shutter speed is one of the big ways in which we control both exposure and motion showing in our images.

Slow shutter speeds leave the shutter open for longer periods of time, allowing more light to reach our sensors for exposure.  They also allow any motion in the subject to blur.  Most of us strive for tack sharp images, so why would we ever use long shutter speeds?

First, sometimes you have to use a slow (long) shutter speed if you’re shooting in low-light conditions.  Second, allowing motion to blur can create some cool artistic effects.  And third, if you need lots of depth of field, you’re going to need a small aperture.  The age-old analogy for the relationship between the shutter speed and the aperture size is to think of a water faucet.  How long you turn the water on is like your shutter speed.  How wide you open the valve is like your aperture.  If you turn a water faucet on wide open for a split second, you can get the same amount of water as if you turn the water on at a trickle but let it run for a much longer time.  That’s how aperture and shutter speed work together to control the total volume of light that will reach your sensor and why using a small aperture usually means a slower shutter.

Let’s start with an example that was both low-light and a small aperture, but with no motion:

AU0A2263

This example was shot at twilight with a 1 second exposure at f/18.  F/18 is a small aperture opening and 1 second is a slow shutter speed.  By using a tripod and a 2-second delay on the shooting mode, I was able to keep the camera still and avoid introducing motion blur.  I got the exposure I wanted and kept everything from the rail in the foreground to the building in the background sharp.

Now let’s take a look at what happens if you don’t keep your camera still:

AU0A2275

In this example, I literally picked up my camera/tripod and moved it in about the last second of a 25 second exposure.  Because the building in the background is so much dimmer than the lights going up the path, the building did not blur while the lights, being so bright, created trails across the image.

Now let’s talk about using long shutter speeds to show motion in the subject itself.  Waterfalls are a popular subject for this technique.  By putting the camera on a tripod again, everything in the image that is still remains sharp but the moving water blurs to a soft “flow” through the image, visually communicating the movement of the water.

Compare this image (shot at ⅙ of a second) to the one after it (shot at 1/320 of a second):

The fast (1/320) shutter speed freezes the splashes of water while the slower shutter speed (⅙) allows the water to blur into softness.  Which one you prefer is a matter of taste (in this case, I like the faster shutter speed better, but that’s partly because it’s slightly less exposed and has less flare from the sun).

Now let’s look at an example of low-light, moving water, and lots of depth of field:

AU0A2305

This was a 20 second exposure shot at f/16.  The small aperture not only provides more depth of field, but it also turns the lights on the bridge into stars.  The slow shutter allows the water coming out of the water cannons to blur into soft streams.  Also notice the surface of the river–the splashes and ripples have also smoothed out into soft lines.

There are many more fun things you can do with a long exposure, but I’ll save those for future posts.  🙂