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 showed you MTF curves for the Rodenstock 105/5.6 HR Digaron Macro on GFX 100S at 1:1. Now I’ll show you the results of testing the same lens at 1:2 magnification, which is close to the magnification that you’d used for digitizing 6×6 or 6×7 negatives.
Here’s the test procedure:
- GFX 100S
- Foba camera stand
- C1 head
- Lens focused to get to 1:2 magnification
- ISO 100
- Electronic shutter
- Indicated f/5.6 through f/8 in half-stop steps
- Exposure time adjusted in M mode
- Cognisys rail, 100 exposures, 80 um step size
- Initial focus 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
Here are the results:
The vertical axis is MTF50 in cycles per picture height. Higher is sharper. The horizontal axis is f-stop.
- The blue and red columns are for the lens on axis, with, respectively, a horizontal and a vertical edge.
- The yellow and purple columns are for the lens at the far right edge, with, respectively, a horizontal and a vertical edge.
These are excellent.
Here is the microcontrast, which for this test I’m defining as the contrast at 1/4 the pixel pitch.
Here’s how the Rodenstock lens compares with the Fuji 120 mm f/4 GF macro:
The Rodenstock lens is a better performer off axis, but the Fuji results are quite credible. Because of internal focusing, the Fuji is faster when they’re both set to f/5.6 and f/8, which reduces diffraction and boosts the results on axis.