This is one in a series of posts on the Fujifilm GFX 100. You should be able to find all the posts about that camera in the Category List on the right sidebar, below the Articles widget. There’s a drop-down menu there that you can use to get to all the posts in this series; just look for “GFX 100”.
I did a quantitative analysis of the Fuji GFX 50S focus bracketing step sizes, and reported the results in terms of displacement of the plane of focus on the sensor in micrometers (um) and in the size of the implied circle of confusion (CoC), also in um. That scores well for precision, and for those of you willing to dust off the lensmaker’s equation and figure out what that means in terms of the object-field focal plane, was all you needed. But a lot of people are more visually than mathematically inclined, and I had nothing for them, in spite of the fact that the GFX cameras do all the hard work to compensate for lens focal length, f-stop, and subject distance to keep the amount of focus-induced blur constant as you change all those things.
After I created the images for the previous post, I realized that I had the material I need to provide a visual cheat sheet for those desiring an aid to picking the step size. I created ten images of a Siemens Star target using a step size of 1. So image #2 is one step away from the starting point if you pick a step size of 2, image #3 is one step away from the starting point if you pick a step size of 3, image #4 is one step away from the starting point if you pick a step size of 4, and so forth.
Here’s the series. Tips on how to use it are below the images.
Say you’re doing focus bracketing. Decide how far out of focus is acceptable by picking a just-marginal image. set the step size to double that (assuming that the most out-of-focus area in a stack is half way in between the steps) or one unit less. If you’re doing stacking, decide how much softness the stacking program can manage, and pick that step size.