By Peter Stewart | 14th Nov 2016
Capturing the bright lights and spectacle of big cities is one of the timeless genres of nighttime photography. As the natural light begins to fade just after sunset, the artificial takes over, allowing for longer exposures with a greater control over illumination of your scene.
Generally speaking, photographing at night is fairly straightforward, however the biggest challenge is in balancing the large variation in luminance between aspects such as a dark evening sky, and the contrasting brighter output of artificial light from things like skyscraper windows, streetlights and moving traffic.
To overcome these limitations of dynamic range that a digital camera can record, we can use a method called exposure bracketing to capture all the brightest and darkest parts of the scene, and then later piece them together. Not only does this allow for greater flexibility in editing to manipulate highlight and shadow detail, but it can produce images with a a very unique visual appeal.
For this tutorial, we will be looking at how to setup, shoot and then edit a typical long exposure cityscape scene.
Auto Exposure Bracketing
Auto exposure bracketing or “AEB”, essentially allows for the camera to take a series of images in succession at different exposure levels, all with just one press of the shutter release.
If you are familiar with using the exposure compensation dial in your regular photography, then thats all we are doing here. We’re making use of the cameras metering system and then adjusting for under and overexposure. The only difference here is that we’re setting up the camera to do it automatically.
Almost all DSLR and professional mirrorless cameras have the ability to take auto-bracketed exposures, so it may be necessary to consult your manual if you are unsure how to enable this feature.
A typical bracketed exposure will take three shots:
- One balanced exposure (for the overall scene)
- One underexposed (for bringing out detail in areas with bright highlights e.g. window lights)
- One overexposed (for bringing out shadow detail e.g. the night sky)
Some cameras will allow you to bracket up-to six or even nine exposures. Whilst this can be beneficial when dealing with extreme lighting circumstances, usually three is more than enough to work with, and we will only be using three for this example.
Long exposure photography of course requires stability, so a sturdy tripod is a must. It is also highly recommended to use a remote cable release to fire the shutter, as this avoids having to touch the camera between shots, reducing any risk of camera shake or misalignment between bracketed images.
Camera Settings & Setup
Here are some basic settings to use for any given setup.
- Set camera to shoot in RAW. This allows for maximum flexibility when later editing.
- Set camera to Aperture Priority shooting mode
- Set camera to it’s minimum ISO (typically ISO 100)
- Use an aperture between f/8 & f/11 for maximum sharpness across the frame
- Set camera to Manual Focus mode (on some cameras this is a switch on the lens)
- Set White Balance to Auto (you can adjust colour balance later in editing)
- Disable Image Stabilisation/Vibration Reduction (IS/VR) if your camera or lens features this.
- Enable Exposure Bracketing (AEB) in your camera menu, and set for three exposures of -2, 0, +1
- Set camera timer to 2 or 5 seconds. This further helps reduce any camera shake.
In order to grab accurate focus, one of the best methods is to enable Liveview, making use of the rear LCD to zoom into 100% and then tweak focus until it’s pin sharp. From here on, the camera must be set to manual focus mode, otherwise the camera will hunt for focus automatically between each bracketed shot.
Here are three bracketed exposures we’re going to work with on this tutorial, taken following the basic setup outlined above.
Nikon D810 + 24mm Lens
ISO 64 | f/8 | 3x Bracketed Exposures - 3sec, 13 sec, 30 sec
Editing in Adobe CameraRAW
Now onto the fun part. How exactly do we merge these vastly different exposures into one workable image? You may have heard terms like HDR or High Dynamic Range, thrown around before, and that’s exactly what we’re aiming to create here. We’re going to take our multiple frames and then combine them into one, allowing for a file with a much greater depth of highlight, shadow and midtone information than the camera would be able to record in a single exposure.
There are a range of software and methods for creating HDR’s out there, with many providing vastly different results.
For this tutorial, we’re going to be focusing on Adobe Photoshop, and using the built in ‘Merge to HDR Pro’ feature to automatically blend our multiple exposures.
This method will generally produce much cleaner results devoid of the issues that plague other HDR editing tools, like ghosting, colour fringing, noise and digital artefacts. Altogether, it provides a much more flexible working file for editing.
If you don’t currently have Photoshop, the Adobe CC package is available here: www.adobe.com/creativecloud
You can even try it free for 30 days, and this includes both the full versions of Photoshop and Lightroom.
The first step is to take our three RAW files and bring them into Photoshop. Photoshop should automatically load into the CameraRAW editor, where we will make our initial adjustments to each of the three exposures.
Starting with our underexposed image, the aim is to reveal colour and highlight information in subjects like the windows and neon lights in the buildings. In our other exposures, bright details like these are commonly blown out and non-recoverable.
We can be quite aggressive with the sliders on this image, as only small fractions will be later used when merging our images to HDR.
Here, we have reduced our highlights and whites sliders to retain as much detail as possible, whilst also bringing back some shadow information by raising the shadows and black levels. Finally, a generous amount of vibrancy to make the colours pop.
Next, we move to our balanced exposure where the bulk of our adjustments will take place. The aim here is to both reduce the highlights, whilst bringing out a moderate amount of shadow detail, in order to make the transition between our under/overexposed images more seamless when we later merge to HDR.
Here, we have tweaked the sliders to get our exposure fairly close to how we would like our final result to look like.
For the overexposed image, we’re looking to only use the areas of the image that are otherwise too dark in the other exposures. So for this shot, we need to make adjustments to bring out more luminance in the buildings for the lower half of the image, and provide a bit of a contrast boost to the night sky.
We’ll begin by reducing the overall exposure in the image. We want our brightness & contrast levels to match well with our previous balanced exposure and to not stand out, so it’s important to make subtle adjustments.
Merge to HDR Pro
With the bulk of our initial edits done, it’s now time to load our images into Photoshop to create our HDR.
Select the three exposures by holding CMD+A (CTRL+A on a PC) and then press ‘open images’
Next, goto ‘File > Automate > Merge to HDR Pro’
In the pop-up window, press ‘Add Open Files’
We can deselect the ‘Attempt to Automatically Align Source Images’ box as our exposures were all shot using a tripod, so there should be no pixel movement between the frames.
Next, press OK to continue and wait for the Merge to HDR Pro window to pop-up.
In the top right, change the ‘Mode’ to ’32 Bit’ then press ‘Tone in ACR’ in the bottom right corner to create our 32 Bit HDR file.
Wait for Photoshop to work it’s magic, and then we’re back in CameraRAW again. This time, we have one 32-bit merged HDR file.
You will notice that our sliders have all returned to their default position, and our merged file is looking somewhat lacklustre.
However, as we are now dealing with a 32-bit image, the dynamic range has increased exponentially, and so we can be far more aggressive with our use of the adjustment sliders, without introducing any detrimental effects like banding or noise.
Dialing our highlights down to -100 and shadows to +100 (yes REALLY that far) we now have a much more flatter image with a balanced range of exposure throughout the frame.
From here, a few mild adjustments overall to Exposure, Contrast and our White/Black levels will reintroduce some depth to the scene and reduce that “overkill” HDR look.
The last step is to convert our image back to a 16-Bit file to save. Press OK to apply our CameraRAW adjustments and return to Photoshop.
From the top menu in Photoshop, select ‘Layer > Flatten Image’
Then select ‘Image > Mode > 16 Bits/Channel’. In the corresponding ‘HDR Toning’ window, change the method from local adaptation to exposure and gamma, leaving the sliders at default. Then press OK.
Thats it! We now have a cleanly merged HDR image.
Here is the final result.
Photoshop’s Merge to HDR Pro feature can be a very simple yet powerful tool for combining multiple exposures. Whether you prefer a more subtle approach or want to dial up the freaky HDR look to eleven, the tool is always there and is a very easy and convenient way to process cityscape images.
Here’s more example images created using this technique.