[This post is revised as of 1/29/2018 with more accurate graphs.]
This is a continuation of a series of posts on the Nikon D850. 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 “D850”. This is equally a post about the Sony a7RIII, and is also tagged as such.
I’ve had two requests for enhancements to yesterday’s post. The first one, as I interpret it, was to make the D850 and a7RIII easier to compare. To that end, I’ve plotted what I consider to two comparable results with both cameras on the same graph. I’ve plotted the green Adobe RGB color. It gets too messy if I plot all three color channels. The A7RIII results are the dotted lines.
The graph presents displacement of the image projected on the sensor from the desired green-channel focal plane. Negative numbers indicate front-focusing. The image-plane shift is in micrometers (um). I’ve made lines indicating the average (aka mean or mu) of the sample set bolder and added thin lines above and below the means that are one standard deviation (sigma) away from it.
The circles of confusion (CoCs) that result from the above:
A reader thought that it should be possible to get a good result with the 58/1.4 on the D850 from f/3.5 to f/8 by optimizing the AF Adjustment for that region. Here are the green channel results when you do that: