Automatic bracketing is implemented on the Sony alpha 7 cameras as a shutter, or drive, mode,. There are two modes, continuous and single shot. If you use continuous mode, the raw (pre-compression) bit depth is changed from 13 bits to 12 bits, just like when the camera operates in continuous shutter mode without auto-bracketing.
- Here is a link to a post about the a7S’s behavior.
- Here’s another.
- Here are some results from the a7.
- Here are some for the a7R.
- Here’s a study of how the a7II’s shadow noise is affected in continuous mode.
If you’re doing handheld HDR, you want continuous auto-bracketing. If you use single shot auto-bracketing, there will be greater camera motion between shots, more work for the auto-registration feature of your HDR program to do, and less chance that it will do the job precisely.
But with the a7 cameras inflicting the bit-depth tax when you use continuous auto-bracketing, you’re going to lose about a stop of DR just for invoking that mode. So, if you select as a bracketing sequence 0, +0.3, -0.3 stops, you’re actually going to be worse off than if you’d not used auto-bracketing in the first place.
To my way of thinking, the minimum continuous auto-bracketing span that makes any sense is 2 stops, and even it is less than a one-stop improvement over no auto-bracketing at all. So use 0, -1, +1 or more when you use continuous auto-bracketing.