Nikonian72 wrote:
In my limited experience, I found that sequentially advancing the focus plane of a stationary camera, slightly changes the lens focal length and makes merging images a bit more difficult. The lens focus on a rail-mounted camera never changes, so the focal length never changes.
Also, accurately step-focusing a lens is much more difficult than accurately step-advancing a rail-mounted camera towards a subject.
I would agree: the incremental movement of a rail-mounted camera is much easier to control and the likelihood that you'll overdo the lens adjustment seems greater to me. One of the things I strive to do when shooting images for focus stacking is to minimize the post production work that would ensue by not being precise enough. By touching my camera as little as possible, I increase my chances of having images that are easier to stack.