Off-axis LoCA of Fuji 45-100/4 on GFX 100s

This is one in a series of posts on the Fujifilm GFX 100S. 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 100S”. Since it’s more about the lenses than the camera, I’m also tagging it with the other Fuji GFX tags.

In the previous post, I looked at the off-axis MTF50 and microcontrast of the Fuji 45-100 mm f/4 GF zoom. In this post, I’ll do the same for longitudinal chromatic aberration (LoCA).

Here’s the test protocol:

RRS carbon fiber legs
C1 head
45, 60, and 100 mm focal length
Target distance as per the table below
ISO 100
Electronic shutter
10-second self timer
f/4 through f/11 in whole-stop steps
Exposure time set by camera in A mode
Focus bracketing, step size 1, 120 to 60 exposures
Initial focus well short of target
Convert RAF to DNG using Adobe DNG Converter
Extract raw mosaics with dcraw
Extract slanted edge for each raw plane in a Matlab program the Jack Hogan originally wrote, and that I’ve been modifying for years.
Analyze the slanted edges and produce MTF curves using MTF Mapper (great program; thanks, Frans)
Fit curves to the MTF Mapper MTF50 values in Matlab
Correct for systematic GFX focus bracketing inconsistencies
Analyze and graph in Matlab

First, I’ll compare the shift in the red raw chanel with respect to the white balanced raw channel, for the 45-100 set at 45 mm and the 45 mm f/2.8 GF lens.

The above plots the shift of the red raw image plane (on the sensor side of the lens) compared to the white-balanced raw plane. Negative displacement is front focusing, and positive displacement is back focusing.

The same thing for the blue raw channel: