Bracketing

Two topics that come up often in our Facebook Group are Bracketing and HDR images. Though these terms are often used interchangeably; they are not. High-Dynamic Range (HDR) photography is a technique used in the photographic process to produce a greater dynamic range of luminosity than possible using standard processes. The goal of HDR photography is to present a similar range of luminosity that can be seen by the human eye; but is not always seen by the camera’s sensor. Bracketing (in photography) is a general technique where several photographs of the same subject are made using different camera settings.

This article will cover both topics; but in a way that photographers of all levels can understand. This very topic is one I struggled with when I was a beginner. It literally took me three trips to Walt Disney World to figure out what I needed to do to make good HDR images. I don’t bring a laptop on vacation with me so I didn’t discover my mistakes until I flew back home to New Jersey. Learning from those mistakes got me to the point where I am at today; and hopefully this article will speed up your learning process, and keep you from making the same mistakes that I have.

Why do we bracket images?

The camera sensor can only see so much. It does not have the ability to see the scene in front of it the way the human eye does. Because of this,  sometimes we take images with really bright highlights or really dark shadows; and the resulting images may have areas which are completely blown out (completely white with no digital information) or shadows that are super dark (with a great amount of noise in the shadows). Although camera sensors are getting better at capturing information, and recovering this information in programs like Lightroom or Photoshop is becoming very easy, most of the time we are left with images that are not what we thought they would be when we took them; or not what we remember seeing when we made the photograph. This is where bracketing comes into play. We take a series of underexposed images to capture the bright parts of the image and a series of overexposed images to capture the dark parts of the image, then we merge them into one High Dynamic Range photograph. This can be done handheld; but it is best done using a tripod and on a subject that is not moving. This is a very useful technique when shooting landscape photography, or in our case—theme parks.

 

How do we bracket?

The easiest way to do this is in Aperture Priority. There is a feature in both Canon and Nikon cameras that is called Auto Exposure Bracketing (AEB). You can set this to automatically take 3, 5, 7, or sometimes 9 images at different exposures. This works great if: 1) you set the ISO, leaving it in Auto for this process is a very bad idea. You want the least amount of noise in your images. So, set the ISO to the cleanest ISO for your camera.  2) The longest exposure in your bracket is less than 30 seconds. The camera will not allow an exposure over 30 seconds in this mode. This is a major problem if you have a base exposure of  10 seconds; and you have set your AEB criteria to bracket –2,–1,0,+1,+2. One stop over exposed would be an exposure time of 20 seconds and two stops over exposed would be 40 seconds. If you use the AEB feature your camera would take the exposures of 10 sec, 20 sec and 30 sec. That 30 second exposure is 1.5 stops over-exposed and may not have the information you need in the image to get a good HDR image later on in the process. This is the part I struggled with for 2 years. I was not getting true 2 stop over exposed images because I trusted the camera to correctly auto bracket. Not fully understanding my equipment cost me big time.

A good video I found online explains how to use the Auto Bracketing feature in cameras. It can be viewed here.

How do I bracket my images?

As I said in the Dark Ride article, there are multiple ways to do this. I am just going to walk through my process when bracketing images.

  1. Set my camera to ISO 100—I want the cleanest images possible to work with and ISO 100 usually does that in my cameras. I may need to push the editing process on these files pretty far and starting with a low ISO greatly helps in the editing process.
  2. Use an Aperture of f/8-f/13—I would like to get everything in my image to be in focus and sharp. Using a smaller aperture will let less light to the sensor but will get most everything in focus. f/8 is the aperture that I normally use; if there is something in the frame where I would like to see a starburst effect, then I will use an aperture around f/13.
  3. Live view to focus—my camera focuses really well in low light but using live view allows me to easily move the focus to the exact spot where I would like it to be. After I focus I turn off the auto focus switch on the lens. Since I am on a tripod there is no need to refocus after every image in the bracket.
  4. Camera Mode—for my night images I set the camera in aperture priority. I do this strictly to get a base shutter speed for my first image. Once I see what the shutter speed will be I switch the camera to bulb mode. Once in bulb mode I click the button on the shutter release remote and use the timer on it to make sure I hold the shutter open long enough for the first image. NOTE: I have a remote cable which has a timer built-in to it. Most remote cables do not have this feature; and you can use the timer on your smart phone to hold your shutter open. With the first image done I now have to do some math. This part is easy once you understand how to do it.

 

 

Shot order Exposure Math Example
1 0 Base exposure. This is the shutter speed I found when using aperture priority 5 seconds
If needed 1 Stop Over Exposed Double the exposure time of base exposure 10 seconds
2 2 Stops Over Exposed Double the exposure time of “1 stop over exposed” 20 seconds
If needed 3 Stops Over Exposed Double the exposure time of “2 stops over exposed” 40 seconds
If needed -1 Stop Under Exposed halve the base exposure time 2.5 seconds
3 -2 Stop Under Exposed halve the “1 stop under exposed exposure time” 1.25 seconds
If needed -3 Stops Under Exposed halve  the “2 stops under exposed exposure time” 0.6 seconds

My sample shots are in a -2, -1, 0, 1, 2 bracket order. Take a look at the differences.

16mm, F/8, ISO 100, 10 seconds. Base Exposure

16mm, F/8, ISO 100, 10 seconds. Base Exposure

16mm, F/8, ISO 100, 5 seconds. -1 Exposure

16mm, F/8, ISO 100, 5 seconds. -1 Exposure

16mm, F/8, ISO 100, 2.5 seconds. -2 Exposure

16mm, F/8, ISO 100, 2.5 seconds. -2 Exposure

16mm, F/8, ISO 100, 20 seconds. +1 Exposure

16mm, F/8, ISO 100, 20 seconds. +1 Exposure

16mm, F/8, ISO 100, 40 seconds. +2 Exposure

16mm, F/8, ISO 100, 40 seconds. +2 Exposure

How I know I captured enough of the dynamic range for the scene?

After I take each shot in the bracket I look at the image that pops up on the LCD screen. I have a setting called “highlight alert” enabled. Anything over exposed in the image will blink in the preview shown on the LCD screen. If something is over exposed in the image I keep cutting my exposure time in half until I no longer have anything blinking in the preview image. As for the shadow areas, I use the preview image for this also. If i still see areas of my image too dark I keep doubling the exposure time and take additional images. Doing this enables me to have a series of images that I can use to blend into a nice HDR image.

Now that I have taken a series of images and loaded them into Lightroom, I can start to make adjustments. My work is far from done at this point. In Part 2 of this article I will explore some adjustments, as well as a few different methods of HDR processing. The methods that I will discuss include:

  1. Photomatix software
  2. Lightroom CC merging
  3. Luminosity Masks in Photoshop

Hope you enjoyed reading this, and check back soon for Part 2!

 

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