Auto exposure bracketing (AEB) is the function by which modern DSLR cameras take multiple photos at different exposures with a single click on the shutter release button. This is a vital tool for HDR photographers. It allows you to shoot HDR photos hand-held and reduces the time it takes to produce an exposure series, thereby minimizing movement in the captured photos.
Most entry-level and mid-range DSLRs available today, however, are limited in the range of their AEB function. They usually do 3 shots with a maximum of 2 EV steps. That is, you can produce a series of exposures with -2EV, 0EV and +2EV for a given scene. This is enough form many situations, but if you want to shoot scenes with a higher dynamic range hand-held, you’re in trouble.
In this article, I will show you a simple way of extending your AEB series from 3 to 6, 9 or even 12 exposures, depending on your camera model and its capabilities. The trick is to switch manually between the modes of your camera and doing an AEB series in each mode in short succession. Virtually all DSLR models on the market allow you to get to 6 exposures using the A (aperture priority) and the M (manual) modes. If your camera has user settings (U1 and U2 on Nikon cameras and C1, C2 on Canon models) you can even extend this to up to 12 exposures.
Assumptions and Requirements
To apply the technique described below, you need to have a camera that lets you switch between the shooting modes on the camera body without taking the camera off your eye. If you have a DSLR, the mode dial fulfills this requirement. Other camera models may have different means for switching.
You will have the highest flexibility with a camera that lets you predefine user settings that you can switch between using the mode dial. The Canon DSLRs that have user settings (C1, C2, C3) include the 7D, 6D, 5D, 40D, 50D, and 60D. In the Nikon line-up, the P7100, D7000, and D600 have user settings (U1, U2). Please check the manual for your camera model to see if it has a similar feature.
The concept is the same for both manufacturers: You dial in specific settings by hand and you can store those settings to one of the user settings. Afterwards, you can quickly recall those very settings simply by turning the mode dial to the respective position.
Semi-Autobracketing Without User Settings
If your camera has no user settings, but only the usual shooting modes (M, A, S, and P), you can expand your AEB series by using the M mode and the A mode. Forget about S and P. Both alter the aperture to change the exposure, and you need a fixed aperture throughout your AEB series for HDR.
The basic idea of using the M and the A modes in combination is the following: You will set up your camera such that you can take the first three exposures in A mode, then you quickly switch to M mode without changing the composition, and you take the next three exposures in M mode. Overall, this will give you a series of 6 exposures (e.g. -3EV, -2EV, -1EV, 0EV, +1EV, +2EV) with the exact same composition. Note that you may also start in M mode and then switch the A mode. The order is not important.
Setting Up Your Camera
Of course, you can vary the procedure to use different exposures and step widths, and I will discuss the different variants below. But for now, let’s look at the step-by-step process for the exemplary series of -3EV, -2EV, -1EV, 0EV, +1EV, +2EV (as dipicted in the diagram above).
- Switch the metering mode to Matrix Metering (Nikon) or Evaluative Metering (Canon). These modes will let your camera evaluate the entire scene to calculate the best overall exposure.
- Switch your camera to A mode.
- Dial in the aperture you would like to use for the scene and choose the appropriate ISO setting. You must not touch these settings again. So choose carefully.
- Activate the AEB mode and set it up to take 3 exposures with 1EV steps (+1EV, 0EV, -1EV).
- Compose your shot and measure the exposure. This will be the 0EV exposure of your entire semi-autobracketing series. Memorize (or write down) the shutter speed for this exposure. Let’s say, that shutter speed is 1/200s.
- Set the exposure compensation to +1EV to shift that entire series up 1EV. So your camera will produce +2EV, +1EV, 0EV exposures.
- Switch to M mode and dial in the same ISO and aperture settings used in A mode. We will now set up the camera to produce the remaining -1EV, -2EV and -3EV exposures in M mode.
- Remember the 0EV shutter speed? In our example, it was 1/200s (see above). The middle exposure of the second AEB series that we are about to set up now is -2EV (2 stops below 1/200s). So you need to double the 0EV shutter speed twice ending up at 1/800s.
- Dial in 1/800s as your shutter speed in M mode. Your AEB function should still be active with 3 shots at 1EV step width.
Taking the Shots
Once you’ve set up the camera, you’re ready to take the source photos for your HDR: You will take two AEB series and switch from A to M mode between the two:
- Switch to A mode.
- Put your fingers on the mode dial such that you can switch from A to M mode without having to take the camera off your eye.
- Compose your shot again (same composition used above to set up the A mode). Make sure that the shutter speed is the same as the one you initially measured while setting up the camera. For the example above, it should read 1/100s (1/200s +1 stop).
- Take the first AEB series in A mode (+2EV, +1EV, 0EV).
- Switch to M mode.
- Take the second AEB series (-1EV, -2EV and -3EV)
- Take the camera off your eye now to check the photos on the display.
- Switch back to A mode and repeat the process if necessary to take another series.
You should do the switching as fast as possible, but you also need to make sure that turning the mode dial does not change the composition too much. While you shoot, concentrate on the scene and try to keep the camera steady. This takes a bit of practice, but it is possible to minimize the movement between the two AEB series to a degree where they actually look like they’ve been taken in one go.
To see how this looks (and sounds) in action (well, at least on my desk), play the short video below.
Semi-Autobracketing With User Settings
If your camera does have user settings, things get a lot simpler. Below, we will just refer to the user settings as U1 and U2. Note that the names may be different for different camera models and vendors. The first four steps are identical to the procedure above: Switch to Matrix Metering, switch to A mode, select your aperture and ISO, and activate AEB mode. Then, you need to proceed as follows:
- Set your exposure compensation to +1EV and store the settings in U1.
- Set your exposure compensation to -2EV without changing anything else and store the settings in U2.
You now have the exact same setting stored in U1 and U2 except for the different exposure compensation that put the middle exposure at +1EV and -2EV respectively.
To commence with the shooting, you do the same as above but now, you start with U1 and switch to U2 after the first AEB series has been fired off. You can also do this vice versa if that suits you better.
Expanding to 9, 12 Or More Exposures
You can also combine the two procedures above and use A, M, U1 and U2 for your series. This will give you 12 or, if you happen to have 3 user settings, even 15 exposures in a single hand-held series. The setup and the math that you have to do gets a bit more challenging, of course.
Note that 6 exposures should suffice in most cases. You will most likely run into problems with low shutter speeds and blurry images if you are doing 12 or 15 exposures hand-held. You will also hit the limit of your camera’s buffer which will slow it down considerably.
Using Different Semi-Autobracketing Setups
In the above descriptions, we used +-1EV steps and set the middle exposures to +1EV and -2EV respectively. But you can also use other settings. The figure below shows a selection of the most useful settings and which dynamic range they cover.
As you see, you can use different middle exposure values as well as different step widths. Use 1EV steps (upper part of the chart) for moderate dynamic range scenes to achieve smooth gradients in the HDR processing. Switch to 2EV steps (lower half of the chart) for scenes with a large or extreme dynamic range. Note how settings with 2EV step widths can be arranged in a comb-like setup (e.g. series no. 6 and 7).
Also note that with middle exposures that are 3ev apart (e.g. -2EV/+1EV and -1EV/+2EV), you can switch between step widths of 1EV and 2EV and gain one additional step on either end of the scale (e.g. series 3 and 6 in the chart) without changing anything else.
Here are a few examples of HDR images taken with this technique. You see the before and after with the source images at the top, the merged and tone-mapped HDR at the lower left and the finished image at the lower right. See if you can find any considerable offset in the source photos.
Summary and Conclusions
In this tutorial, you’ve learned how to overcome the limitations of many entry-level and mid-range DSLRs for hand-held HDR shooting.
Instead of being stuck with 3 shots in auto exposure bracketing mode, you can now virtually take as many as you like with just a little bit of additional setup time and manual switching. With a bit of practice, you won’t notice a difference to series shot with more expensive cameras.
But now back to you: Go out and try it. And don’t forget to come back here and share your experiences and additional tips for semi-autobracketing with your specific camera.