Technical Analysis: Fujifilm GFX, GFX IR, IR Hot Spots, Adapted Glass, and More


Jim Kasson published more testing with the Fujifilm GFX Cameras after our last post. Below are quotes and links to all of his great technical testing that he makes available to the public completely free of charge since we last checked in:

The Last Word – Diffraction and sensors

The question of the visibility of the diffraction has two answers, depending on how you ask the question. If you ask the question “when does the diffraction dominate the sharpness of a well-focused subject”, then the size of the pixel aperture is important (not the pixel pitch: that affects aliasing). When a lens is stopped down to f/11, f/16/ or f/22 and focused accurately, it is likely that the lens aberrations are unimportant compared to the blur induced by the Airy disk. The size of the blur at the sensor is, neglecting phase effects, equal to the size of the convolution of the effective pixel aperture and the projected Airy disk. If the Airy disk is much larger than the pixel aperture, then virtually all the blur you see in the image will be due to the diffraction.

The Last Word – Does repeated JPEG compression ruin images?

Conclusions

  • In Photoshop, JPEG recompressions don’t “walk”; they are the same after the first iteration.
  • Changes from the first to the second iteration are small.

The Last Word – Leica 90/2 Apo-Summicron ASPH-M on GFX 50S

The captions are the subject distances. It’s not an internal focusing lens, so I thought it might do better at close focusing distances. Maybe it does, but not enough to make much difference.

It’ll be fine for square shots, and maybe OK for 4:5 aspect ratio ones, but not for 4:3.

Things improve a bit if you stop down, but the reason to use this lens is to use at between f/5.6 and f/2.

The Last Word – IR images without demosaicing, revisted

There’s a little more contrast in the balanced image, and it is maybe a hair sharper. I’ll bet I could sharpen up the AHD image to make the sharpness equivalent, though.

My take is that there’s not much to be gained from this technique that applies to real-world photography.

The Last Word – Leica 280/4 Apo-Telyt R at 950 nm on GFX 50R

I guess the question is going to be whether to use the lens at f/8 and deal with the slight vignetting, or to use it at f/11 and suffer the diffraction, which is about twice as bad at 950 nm as it is in visible light. I’m thinking that f/8 is the plan.

The Last Word – Fujifilm 250/4 in 830 nm infrared on GFX 50R

I put a B+W 830 nm lowpass filter on my LifePixel-modified (720 nm option) GFX 50R and checked for hot spots on distant scenery with a +100 contrast boost.

The Last Word – Leica 280/4 Apo-Telyt R on GFX 50R in infrared

This is a useful lens with some minor advantages over the Fujifilm 250. It’s more compact, and has a much better — dentented! — collar. If you’re making long series of exposures, you can be confident that the focus won’t drift, which is not something you can say about the Fuji 250.

The Last Word – CO 60/4 UV-VIR-IR on IR-modified GFX 50R

The Schneider lens is much less expensive than the CO macro, and would probably be more cost-effective. The CO lens does have hotspots at some macro distances.

The Last Word – Infrared hotspotting

Yesterday, I received a Fujifilm GFX 50R back from LifePixel, who had modified it with a 720 nm infrared conversion. The modification consists of the removal of the IR-blocking filter — aka hot mirror — and its replacement by a filter that blocks visible light and passes infrared light with wavelengths shorter than about 720 nanometers.

The Last Word – Full frame fisheye on GFX 50R, Z7

f you’ve managed to find a smart adapter for the GFX that takes Nikon E lenses, it’s worth a try.

The Last Word – Schneider 90/4.5 Apo-Componon HM on GFX 50R, f/5.6, f/8

Looks like f/8 is the sweet aperture for this lens. It also looks like there’s some room for movements.

The Last Word – Schneider 90/4.5 Apo-Componon HM on GFX 50R

That is quite sharp. Lots of aliasing, thanks to the small pixel apertures on the GFX 50x cameras… This is good performance, but with respect to the corners, my socks are firmly in place. I’ll try stopping it down a bit.

The Last Word – Sony 135 STF on GFX-50R, bokeh visuals

Now I’m going to let you see what the bokeh looks like in images, both with transition-focus areas, and far out of focus ones.

The Last Word – Sony 135 STF on GFX-50R, bokeh

There are two pieces to bokeh. The first is what things look like when they are well out of focus (OOF), and the second is how the transition from OOF to in-focus happens. The second is complicated, but the first is simple.

The Last Word – Sony 135 STF on GFX-50R, sharpness

That is quite sharp. Lr’s demosaicing is providing a little sharpening, too. The small microlenses int he GFX 50x cameras are doing their part.

The Last Word – Sony 135 mm STF on GFX 50R

To my surprise and great pleasure, it covers the 33×44 format with no vignetting.

The Last Word – Fuji 30/3.5, 32-64/4 on GFX 50x, foliage

Diffraction has equalized things. These lenses are very close in this test.

The Last Word – Fuji 30 mm f/3.5 OOF PSFs

There is not much physical vignetting, which shows up as “cat’s eye” shapes off axis. There is a slight bright ring around the outside of the PSFs, which will cause the bokeh to be edgier than it would be if they were flat disks. The onion ring artifacts are minimal.

I call this reasonably good performance. Quite acceptable, considering that hardly anyone buys a wide, fairly slow lens for its bokeh.

The Last Word – Fuji 30 mm f/3.5 focus curvature

I used the quick-and-dirty focus curvature test (Photoshop > Filter > Stylize > Find Edges, then convert to B&W) on a picture of my driveway and entry pavers with the 30 mm f/3.5 Fuji G-mount lens wide open on a GFX 50S.

The Last Word – Fuji 30 mm f/3.5, 32-64 mm f/4, GFX 50S, Siemens Star

I used to say that the Fujifilm 32-64 mm f/4 was the second best zoom I’ve ever used — after the Nikon 180-400/4. But then the Fuji 45-100 f/4 came along and I decided it was a two-way tie for second. The obvious standard for judging the new Fujifilm 30 mm f/3.5 is their great zoom, and that’s what this test is about. I used a low-contrast Siemens star for a target.

The Last Word – Fuji 30 mm f/3.5 screening test

The Last Word – Fuji GFX auto focus bracketing step size

Using a GFX 50R and the 23mm f/4 lens, I counted the number of exposures the camera made to go from 1 meter to infinity in auto mode, and manual mode with step sizes of 10, 5, and 2.

The Last Word – How focus-bracketing systems work

With both the Nikon and the Fuji systems, the first step is to pick the step size based on your tolerance for blur in the stacked result. Then pick the near focal distance. Experiment to see how many shots will be necessary to get to the desired far focal distance, varying the f-stop if you wish (a narrower f-stop will require fewer steps; f/11 will require half as many steps as f/5.6.).** Once you’ve done this a few times, you’ll have a pretty good idea how many steps it will take. If the lens is longer or the subject is closer, it will take more steps. When you get really close, it will take a lot of steps, and you may wish to allow more blur by making the step size larger. At 1:1, image space is a mirror of object space, and the step size in the image field will be the step size in the object field; that means steps in the object field of a few micrometers.

The Last Word – Photography and trade-offs

Fifty years ago, I used to occasionally do exposure bracketing. I stopped doing that, because I found that, by intentionally making images at other than what I thought was the right exposure, I minimized the probability that the correctly exposed image had all the other elements that I was looking for (It was also expensive, which is no longer an issue).

The Last Word – Fuji 23/4 on GFX 50R, 20/1.8 Nikkor S on Nikon Z7

In this case, you get what you pay for. On the other hand, you can make quite nice landscape photos with the 20 mm Nikkor and a Z7.

The Last Word – Metabones 1.26x Expander on GFX 100 with Otus 55

I consider this an impressive performance for the Metabones expander. You’ve got to expect some loss in quality with a teleconverter, but this is quite modest. Of course, as with most adapters, I would expect the degradation to vary with the lens, with the shorter lenses being the most problematic. But that’s a test for another day.

The Last Word – Camera differences in Adobe Color Profile

The Last Word – Calibrating out the camera when making color profiles

The Last Word – Chromaticity shifts with the a7RIV, Z7, and GFX 100

The Last Word – Camera differences in color profile making

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Fujifilm GFX100S: B&H Photo / Amazon / Moment / Adorama
Fujifilm GFX100: B&H Photo / Amazon / Adorama
Fujifilm GFX50R: B&H Photo / Amazon / Adorama
Fujifilm GFX 50S: B&H Photo / Amazon / Adorama

Fujinon GF80mm f/1.7: B&H Photo / Amazon / Moment / Adorama

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