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DSLR Next Steps – Exposure Bracketing

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Now that we have taken a look at exposure basics and exposure compensation a good next step is to review exposure bracketing. Exposure bracketing is a feature found on most cameras, but not all. For example, several Nikon entry DSLRs lack this feature*. However users of these models should read this article to see if this is a must-have feature on their next camera.

Exposure bracketing has been used in photography literally forever. Bracketing exposures is simply the practice of taking one exposure at the recommended setting (usually from a meter) and then one or more additional exposures above and / or below that setting.

Bracketed Readings

The practice of exposure bracketing started as a way to get ‘insurance shots’ when shooting in difficult lighting situations. As cameras became more sophisticated and electronic, automatic exposure bracketing (AEB) came to be.

The program-type film cameras of the 1990’s brought some basic automation to the process. The AEB setting would capture three images: one matching the meter, one over the meter and one under the meter. The photographer could specify the range of the bracket, usually between 1/3 stop and 2 stops, over and under. Photographers that used transparency (slide) film frequently used exposure bracketing because transparency film is notoriously unforgiving of exposure errors.

Funny thing, today’s digital cameras have many of the same characteristics of slide film. Unlike color print film, digital cameras and transparency film have a very narrow range of acceptable exposure. A little too much over exposure and we lose detail in bright areas, a little too much under exposure and detailed dark areas go black.

One use of AEB allows the photographer to capture three quick shots, each at a different exposure value, and later choose the better exposed image as a keeper. In this case “better” refers to the image that offers the best recording of important details.

A Range Of Bracketed Shots
A range of exposure bracketed image files.

But what if we could take the best of all three bracketed exposures and combine them into one image? Thanks to digital imaging we can do just that. The process is known as image merge or High Dynamic Range (HDR) photography. Digital software such as Photoshop, Photoshop Elements and Photomatix make it easy to turn bracketed images into a composite.

Compiled Bracketed Shots
Bracketed shots compiled with software into a single image.

We have one big caution for photographers new to using AEB on their cameras. Once set, most cameras will remain in AEB exposure mode until the mode manually turned off. Even after the camera has been powered down and left idle for a few days. Avoid nasty surprises; always check your camera’s LCD panels to confirm current settings!

Summary: Auto exposure bracketing is a handy tool when photographers are confronted with complicated scene lighting or lighting that covers a very broad range. Cameras that offer AEB will allow the photographer to set the range of the bracket, often from 1/3 stop up to 2 full stops of variance from the meter reading. By selecting AEB and capturing three exposures across several stops the photographer is able to select the image with better exposure after the fact. A relatively new use for bracketed exposures is in creating composite images using software to create an image with the best exposure values from each captured image.

Please Note: There can be a difference between shooting with the camera set to capture JPG vs. RAW images. Without digging into a lot of technical detail, about two stops more information is available in RAW mode vs. JPG. It is possible with appropriate software to create three bracketed shots from one RAW image file: on target, +1 stop, -1 stop. Though the software may permit a broader stop range to be extracted from the bracketed images, few cameras can provide image files that contain enough image information to make broader stop ranges practical.

*Nikon DSLRs without auto exposure bracketing – D40, D40x, D60, D3000, D3100

DSLR Next Steps: Exposure Compensation

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DSLR Next Steps – Exposure Compensation

Introduction

Now that we have an understanding of exposure and how the camera’s automated exposure modes work we’re ready for the next step. For all of the automation built into today’s cameras there is no better judge of picture quality than our own eyes. After we have used our cameras for a short while in its various automatic exposure modes we soon notice that a few images just aren’t quite right. Maybe the subject is a little too washed out, or perhaps the terrain in a landscape looks darker in the image than it did to our eye. It’s tempting to blame the camera for these near misses and shrug them off, but what we have uncovered are actually the limitations found in any camera’s automatic programming. The good news is that with a little practice and experience we can anticipate these instances and quickly overcome the limitation with an easy to use tool built into every DSLR camera.

It’s OK To Be Biased!

The concept is pretty straightforward. As illustrated by the little green guy at the top of the page, the camera’s exposure automation still does its job and creates an exposure based on its programming, in this case f/5.6 and 1/125th shutter speed. We can simply choose to bias the outcome toward overexposure or underexposure. We do this by moving the camera’s exposure up and down on a master scale divided into stops and fractions of stops.

For example, experience tells us that our cameras in automatic exposure modes will always underexpose in certain situations – such as when we take pictures in the snow:


In this example image the camera’s meter reacted to the highly reflective snow and underexposed the image. What we need is a way to bias the automation so that it increases exposure and gives us a better picture.

The tool we use to bias exposure is called ‘Exposure Compensation’. Using this tool we are able to tell the camera to bias its exposure settings toward overexposure or underexposure. In the case of our example shot if we set the exposure compensation to overexpose by just over one stop we get this image:

The snow is now white and the fruit is properly exposed.

In fact it is possible to make this generalization: Anytime we shoot pictures on snow fields, on beaches or even on the water it is a good bet that +1 to +1 1/3 stops overexposure compensation is going to give us better images. Pictures of brides in white wedding dresses benefit from positive exposure compensation too. When the subject or the surroundings are highly reflective and well lit our exposure meters and automation can be fooled into underexposing.

Make It Black

Of course there is an opposite side too. Sometimes we want to bias the camera to underexpose the scene. By underexposing a darker scene we don’t let any bright areas or lights burn in too much and we force shadows toward inky blackness.
Here is a sunrise as the camera’s program wanted to expose it:

And here is the same sunrise with -1 stop of exposure compensation forcing an underexposure:

The effect on the sun and in the color and definition of the clouds is where the benefit of underexposure is the most noticeable. The exposure that the camera made on its own tried to strike a balance between the darker beach and the brighter the sky. The result was that the sky and sun were over exposed.

In complex or high contrast lighting situations the camera’s meter will try to create a middle value exposure. By using exposure compensation we bias that middle value toward an overall darker or lighter rendering of the scene. Exposure compensation allows the photographer to have a say in the image outcome without completely giving up camera automation.

The Eye Of The Beholder

Using and setting exposure compensation values is totally under the control of the photographer. This is an area populated with guidelines and not hard and fast rules. Using or not using exposure compensation, and if used how much, is totally up to the photographer. We have given two suggestions in this article: Dial in overexposure for bright / reflective scenes. Choose underexposure for darker scenes with bright areas. However experience with your own camera and lens coupled with the subjects you like to shoot will guide you in using exposure compensation to create the images that please you.

Exposure compensation controls vary by camera and model so we will have to refer you to your instruction manual for guidance in locating the correct buttons, rollers or switches. Many compact cameras also have exposure compensation controls as well. Look through your existing images and find examples that exposure compensation might have improved. Then the next time you shoot in that situation dial up some over- or under- exposure bias and see if you can outdo your last effort!

A word of warning: Exposure compensation in most cameras won’t reset to zero when the camera power is turned off and then back on. We strongly recommend that photographers develop the habit of confirming all settings on the appropriate camera LCD screen before each new shooting session.

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