Shooting star trails

In our last article we learned how to shoot all kinds of light trails, now we're going to take a deeper look at how to shoot star trails.

First of all. What are star trails?

When you look at the stars at night, they seem to be stuck, but if you stare for a couple of minutes you'll start to realize that they're moving, only very slowly. This effect is created by the earth's rotation and not by the movement of the stars themselves. Every star in the sky makes a whole turn around the pole star. This particular one is right in the axis of the earth's rotation and this causes it not to move in the sky and always head north, that is why this star has been used by travellers thousands of years ago to guide themselves in the night, yes I like science :D but we're moving away from our main topic.

What is the effect of this motion when we shoot stars at night?



If we shoot stars with a shutter speed long enought to capture this movement, the stars will create trails in the form of circles around the polar star, decorating our shot with a very interesting sky.

How do we set up our camera to achieve these results?

This will be a little more complicated than with standard light trails. First of all you will need a remote control, or any other device that allows you to use the bulb mode of your camera. Setting up the maximum 30 sec exposure configured in your camera won't be enough to capture the star's movement.
To set up bulb mode we'll need to go into manual. Se the ISO to minimum, aperture preferably to a high value and shutter speed to bulb mode. Set the focus to manual and focus on infinity.
I also recommend using a long focal length because stars will appear to move faster when the lens is zoomed in.

And this is it, you can start to experiment with different compositions and shutter speeds, keep in mind however that very long shutter speeds will create too much noise in the image, remember turning the noise reduction function of your camera to minimize this effect. If you want to have longer trails, you can create a series of relatively short exposures and then blend them together in photoshop.



It is important to be able to identify the pole star, since all the stars will turn around it, making it a strong subject of your composition. To find it look north and find a very bright star.

And last but not least, keep in mind that this kind of photography works best at clear skies without luminic contamination, so run away from big cities.

Photographs by Corica, Warner Strauss and me.

Shooting light trails

If you've read the "Mastering the basics" section you already know a lot about how to use the exposure settings creatively. In this article we're going to take a look at using long shutter speeds to get light trail pictures.

What you're going to need:

A tripod. When shooting at speeds longer than a second the use of a tripod is a must, trying to take these images handheld will result in very blurry images. You can however try to lay the camera on some stable surface but this limits your creative possibilities a lot.

A DSLR or Bridge Camera. Most point and shoot cameras don't allow for exposures longer than 1 or 2 seconds so we'll need to use a DSLR or bridge camera that lets us choose the shutter speed.

How is a ligh trail created?

The creating of light trails is very simple. When we let the shutter open for a long time any bright light that goes through the camera's field of view, will create a trail of light through the image. Used properly these trails can create very nice effects on roads and can be an interesting addition to a cityscape shot.

The first thing you have to do for getting a light trail shot is finding a place with moving lights, a typical location to start at is a driveway. Set your shutter speed to a value between 5 and 30 seconds, I recommend using the Shutter speed priority mode . Now mount your tripod and frame the shot. Once a car approaches, click the shutter button. The lights of the car will create a light trail on the image as long as the shutter is open. Review your results and try using different shutter speeds.

Using flash. Although flash is not often used in light trail shots it can create a nice effect showing the object that creates the trail and the trail itself. I recommend using rear curtain flash, in this mode the flash is shot just before closing the shutter and it makes the subjects lit by the flash appear at the end of the trail. Something like this:

Going back to the techincal aspects, i recommend using a low ISO and enabling noise reduction in your camera's menu to reduce digital noise from the long exposure.

An interesting addition to our gear if we want to shoot light trails often is a remote control. Triggering your camera from a remote has 2 advantages:

1. We won't need to touch any button on the camera, eliminating every chance of creating blur in the image.
2. It will allow us to use bulb mode, in this mode you'll be able to open the shutter with one click of the remote and closing it with a second click. This way you can't exactly control how and where the trail is created.

A very special kind of light trail are star trails, but we'll talk about that in the next article so stay tuned!

Mastering the Basics: Understanding Aperture

After having learned about shutter speed and ISO settings, now we're going to take a look at the aperture.

The aperture setting is the size of the opening in the lens.

Every lens has a couple of blades, called iris, that are put together to regulate the light that gets through, depending on the aperture setting used.

The aperture is indicated in the camera as the f number. A high f number will represent a small aperture while a small f number will represent a big one. This might sound counterintuitive but is easier to understand if we imagine the f number in the formula 1/f. The higher the f number the smaller the end result.

But enough with the technical details, what is aperture good for?

Tweaking the aperture settings will not only control the light intake, but will also control the size of the depth of field (In short, the depth of field is the part of the image that is in focus). This will allow us to use the depth of field that we find appropiate for our shot. Imagine for example that we are taking a portrait picture. We want everything in the background to be out of focus, so that it doesn't distract from the main subject. In order to achieve that we will use a small f number, that will result in a big aperture, creating a shallow depth of field.
If we were shooting a landscape for example we would do the exact opposite so that all the parts of the image stayed in focus.

The maximum aperture setting will depend from each lens and is an important factor to have in mind when buying new gear, prime lenses, those without zooming possibilities, are the ones which allow higher apertures. It is easy to find cheap prime lenses allowing for f1.8 apertures and more expensive ones even allow for f1.4 or f1.2. Zooming lenses instead have smaller apertures and their maximum aperture varies depending on the focal length used. The 18-55mm kit lens from the D40 for example will allow for a f3.5 aperture at 18mm but only f5.6 at 55mm. Zooming lenses with bigger apertures are only found in the professional level and are used by sport photographers for being able to capture fast shots even in low light.

Summing up, rising the aperture setting will let in more light while making the depth of field smaller and the maximum aperture depends on the type and the quality of the lens.

Mastering the Basics: Understanding ISO

In the last article about the exposure triangle we took an in-depth look at the shutter speed and we mentioned how sometimes it was better to use a slow shutter speed than a high ISO. Now we're going to analyze why this happens.

First of all what is the ISO setting?

The ISO setting represents the sensors sensitivity to light.

Getting into more technical details, the ISO setting in digital photography is the gain of the sensor's signal. Although we speak about digital photography the camera's sensor itself is an analog device, just like a microphone for example, and as such its signal can be amplified to get more light into the picture.

This can be useful because it will allow us to use a faster shutter speed or smaller aperture when we need it (see article about shutter speed), but amplifying the signal will create noise, which will translate into small color dots in our image like in this example photograph. Depending on the camera and the ISO setting this noise can go from slightly visible to spoiling our image. Most modern DSLRs will be able to handle noise from ISO 200 to 800 at acceptable noise rates, but it's always a good idea to keep ISO at its minimum and only rise it when the we're forced to.
As an example a typical situation where you're forced to rise the ISO is at concert photography, where there is dim light and you can't use slow shutter speed because the subject would be blurred, in that case you can only rise the ISO, although you know you will have an image with some noticeable noise.

Summing up all you need to know about ISO is that you have to keep it as low as you can by using, when possible a slow shutter speed or a big aperture.

Mastering the Basics: Understanding shutter speed

In my last article I mentioned how tweaking every setting to get the correct exposure had it's pros and cons. The first setting we're going to take a look at is Shutter speed.

The Shutter speed is the amount of time that the camera's sensor is exposed to light.

This simple setting has a great impact on the end result of the photograph. Using a fast shutter speed will freeze the moment, while a slow one will capture motion in the shot.
Keeping this in mind is very important because we will need to change this setting often depending on the type of photography we're doing. A classic example for this is sports photography. At sports events we're often photographying fast moving subjects, so we will need to set a fast shutter speed to capture the moment.
Sometimes though we will want the photograph to show the movement in the scene. Using a slow shutter speed moving objects will be blurred giving the viewer a sense of speed.

The problem with slow shutter speeds is that it's difficult to hold the camera completely still, so at certain speeds the whole photography will become blurred.

Sometimes we will need to use a slow shutter speed because there isn't enough light available even when rising the ISO and aperture. When this is the case it is very useful to use a tripod that will allow us to have the camera completely still during the exposure of the shot. Using a tripod will also allow us to use very long shutter speed to create interesting effects like light or star trails, which we will talk about in further articles.