How to Shoot Long Exposure Light Trails - Peter Stewart Photography
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  • How to Shoot Long Exposure Light Trails

By Peter Stewart | 1st Dec 2014

This is a short and simple tutorial that will show you an easy method for capturing great night images of events like laser light shows, fireworks, lightning and light trails of cars or trains. 


For this method to work, you will need the following:

- A camera with a bulb mode setting

- A sturdy tripod

- Optional but recommended - a remote timer or cable release

- A basic knowledge of Adobe Photoshop


The Method


The idea here is simple. Imagine we have an event like the below example. A 15 minute laser light show over Marina Bay in Singapore. Impossible to capture all 15 minutes of it in one exposure as the frame would likely turn out white from overexposure, yet one 30 second or shorter exposure would not do the spectacle any justice. 

The idea here is to take multiple exposures and then later, combine all the shots together to make one image. 

Luckily, it's one of the simplest tricks to pull off in Photoshop.

20+ images blended together to show the full 15 minutes of the nightly laser light show


Camera settings and shooting


In this example, we have a busy flyover with multiple train lines passing over an equally busy highway. Perfect for light trails. 

The aim is to capture a frame every time a train passes over the bridge, whilst also capturing as many light trails as possible of the traffic on the highway. 


Settings

- Camera on tripod attached to remote timer or cable release.

- Camera set to Bulb mode with lens set to manual focus and image stabilization set to Off

- Aperture setting between f/8 to f/11 for maximum depth of field and to allow for longer exposures

- (optional) Camera set to mirror up or mirror lockup mode


To begin, it's a good idea to take a base exposure, or 'plate' as it is sometimes called. This will act at the starting point upon which you will later overlay subsequent frames. Using an aperture of f/11, a 30 second exposure should be sufficient to capture enough ambient light in the scene and ensure you get a clear and bright shot of the night sky (see below left shot).


Next, without moving the camera (don't even think about checking that image preview!) you can start firing away with more and more shots, which will later be overlaid in the computer to form your final image. In this example, I waited until a train passed over the bridge, manually fired off the shutter with my remote and left it open until the train had passed through. Usually this was no longer than 6 to 10 seconds. Generally, you want to keep your shots under 10 seconds, otherwise colored light streaks can overexpose and turn into white light. 


So to summarize; 

- Take one 20 to 30 second exposure as your first shot. 

- Take multiple follow up exposures at shorter bursts between 5 to 10 seconds each. 




Post-Processing


Now that we have all our shots done, we are ready to move into Photoshop and start combining our exposures together.  


To begin, select all your image files and open these in Photoshop. If you are shooting in RAW (no excuses not to) then your files should load up firstly in Adobe Camera RAW interface. 

This gives us an opportunity to do some quick editing of our files before bringing them into Photoshop proper.

Ensure that you have Select All  pressed and then make adjustments to your base exposure as you wish. In the example below, I have my 30 second exposure selected, where I've boosted vibrance, contrast and upped the vibrance. These adjustments will carry over to the other shots too. 

With the files loaded in Photoshop, my first tab will be my base exposure upon which I will layer the other exposures on top.

The next step is simply to go through each tab and copy and paste that frame over into your first tab, thus creating layers above your base exposure. 




Once you have copied and created layers for all of your frames, simply select them all by pressing CMD+A (OSX) or CTRL+A (PC) and then goto the blending mode dropdown list and select Lighten





By selecting the blending mode Lighten , Photoshop will only overlay the brightest parts of each frame whilst preserving the overall ambient light, which is perfect for these types of shots. Below is the effect after all the frames have been combined. You can now see increased headlight trails from the traffic below, as well as the single long trails from each passing train. 

And here is the completed shot, after some more post-processing to add a split color tone and increased contrast.

Thats all there is to it really. It's as simple as overlaying multiple shots in Photoshop, and merging them together though the Lighten blending mode. 


Here are a few more completed examples of this technique


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