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”.
A few days ago, I posted more images of distant foliage with the Fuji 80 mm f/1.7 GF lens, and proclaimed it fit for landscape use. Not so fast, said Joseph Holmes, whom I greatly respect, you need to consider field curvature. So this is the result of some testing with the same subject with a protocol designed to test for field curvature.
The scene, with the central tree about 100 meters away. At that distance, recomposing with a rectilinear lens will produce a focus error with a CoC of about 2 um at f/1.7, and well under 1 um at f/5.6.
- RRS 4-series Versa legs
- Arca-Swiss C1
- 2-second self timer
- ISO 100
- Manual focus at taking aperture, focusing once with the subject tree (you’ll see) centered.
- Two more shots with the focus the same with the tree on the far left side and in the upper left corner
- f/5.6, f/8 for the 80
- Three sets of images at each aperture.
- 1/200, 1/100 second shutter speed with f/5.6 and f/8, respectively
I developed the images in Lightroom with
- White balance set to Daylight
- Adobe Color Profile
- Sharpening: amount 20, radius 1, detail 25
If you’ve seen these here before, just jump to the images. If not, I need to spend some time telling you how to interpret them. They’re at roughly 250% magnification, enlarged to 700 pixels high on export from Lightroom. If you just want a rough idea of the differences, just look at the images as displayed in-line in the posts. However, if you wish to compare these images in detail, you should view these images by clicking on them to see the source files, then set your browser for 100% zooming. Even better, download them and make Photoshop stacks.
No matter what you do, these crops are all going to look horrible. I’m blowing them up so much so that they will represent the original file after JPEG’s discrete cosine transform has had its way with them. If you want to get a good idea of what the images would look like printed, get far away from your monitor. No, farther than that. Put a bunch of the images up on the screen and back up until the best one starts to look good. Then look at the others. There’s another reason why these images won’t look like the best thing the camera/lens combination can deliver. They’re demosaiced with Lightroom. Lightroom is not awful, but for a particular image, there are usually better raw processors. I use Lr because it’s a de facto standard, because I know it well, and because it’s got good tools for dealing with groups of images.
Here’s how to use these highly-magnified crops. The dimensions of the GFX 100 sensor is 11648×8736 pixels. If we make a full-frame print from the GFX 100 on a printer with 360 pixels per inch native driver-level resolution, like the Epson inkjet printers, we’ll end up with a 32.4×24.3 inch print. The 399×309 pixel crop you’re looking at will end up roughly 1.2×0.8 inches. Let’s imagine that you or your viewers are critical, and will look at the 32×24 inch print from about 24 inches (conventional wisdom is that the distance would be a little greater than that, or 40 inches (the diagonal), but you did buy a high-resolution camera for a reason, didn’t you?).
The next step is dependent on your monitor pitch, which you may or may not know. Turns out, you don’t have to know it. Just take the crops and view then at 1:1. How high are they? Get out your ruler and measure, or just guess. Let’s say they are 6 inches high. 6 inches is about 6 times 0.9, so in order to view the crops the way they’d look from 24 inches on the print is to view them from 6 times as far away, or 12 feet.
An issue with the test protocol I used is that the focus could be a little bit off in the center image, and depending ono field curvature, that might help or hurt the sharpness of the off-axis images. So I will show you all three seds of images.
First at f/5.6:
There is some loss in sharpness in the off-axis images. I don’t consider it disqualifying for landscapes.
f/5.6, center, #2
Now the differences are less significant.
Not much difference.
About the same as the first two sets of f/8 images.
I still think this would make a pretty good landscape lens.
As a bonus, a 16-shot stack. You can’t normally get away with this for landscapes, but it was a very still morning.
That is so clean that you can amp up the sharpening without exciting visible aliasing:
Another reasonable question is how much of the corner softening is due to focus curvature.
Here are a two pairs of shots where the camera was refocused in the corners.