Auto Exposure Bracketing guide

What AEB is

Auto Exposure Bracketing is a firmware routine that captures a sequence of frames at exposures scaled around the metered base value. It exists to overcome the sensor's physical limits: full well capacity clips the highlights, read noise drowns the shadows.

Merging the frames in post (HDR merge) yields a synthetic dynamic range wider than anything a single exposure can record.

The formulas

Each frame's exposure value follows the fundamental photometric relation; the sequence's coverage grows linearly with frame count and step size.

What the camera varies

In aperture priority (A/Av) the firmware keeps the aperture fixed — preserving depth of field and optical rendering — and modulates shutter speed. In shutter priority (S/Tv) the time stays fixed and the aperture changes. In manual (M) the shutter speed varies, or ISO if Auto ISO is enabled.

For tripod HDR the recommended mode is A/Av or M: changing aperture between frames alters depth of field and vignetting, complicating the merge.

Why the firmware limits exist

Frame and step limits reflect engineering trade-offs: long sequences with wide steps mix very different shutter times and stress the buffer and memory controller; that's why Nikon, Sony and Panasonic cap the step on 7- and 9-frame sequences, while Fujifilm and Hasselblad delegate the latency to a high-speed bus.

Extended sequences also wear the mechanical shutter; the electronic shutter eliminates that wear but introduces rolling shutter on moving subjects and possible banding under artificial light.

Practical advice

On modern BSI and stacked CMOS sensors a short sequence with a wide step (2 EV or more) beats many frames at fractional steps: less total capture time, less risk of movement between frames, the same merged result.

Three frames at ±2 EV cover most real scenes; five frames at ±2/±3 EV handle interiors with windows and extreme backlight. Use a tripod, lock focus and white balance, shoot RAW.