Fujifilm GFX100 Technical Analysis Part 2: Electronic Shutter Speed, PDAF Banding, and More

Jim Kasson has continued his analysis of the Fujifilm GFX100’s capabilities at a rapid pace, which is why we have another technological mega-post today of his findings. You can find the first post here and for those of you that have been asking about electronic shutter speed, it’s 1/3 – 1/6th, which you can read more about below.

The Last Word – Fuji GFX 100 sharpness, LoCA, focus shift with 110/2

  • F/2.8 is the sharpest f-stop at this distance

  • f/2 and f/2.2 are a fair amount softer, but f/2.5 is very sharp.

  • You don’t lose all that much sharpness even at f/5.6, but the sweet spot of the lens is between f/2.5 and f/4.

  • There’s enough focus shift that you should focus at the taking aperture.

  • The MTF50s obtained are about the same as I got earlier with the same lens on a GFX 50S.

  • That means that the pixel-level sharpness of the GFX 100 is less than the GFX 50S, and the picture-level sharpness is about the same. (This will need some more looking in to.)

  • If you don’t want to bother with the graphs, I’ll bottom-line it: there isn’t very much LoCA at all.

The Last Word – Fujifilm GFX 100 sharpness compared to GFX 50s

Now you can see that the GFX 50S has a higher modulation transfer function from about 60 cy/mm on up. That seems to imply that it has an even smaller effective fill factor than the GFX 100, in spite of the GFX 100’s much finer pitch (assuming the GFX 100 fill factor is 100%, this is a rough confirmation of Jack Hogan’s work on the GFX 50S microlens size a couple of years ago). Both curves stop at the Nyquist frequency for each camera. You can see that the GFX 50S, with an MTF of more than 0.6 at the Nyquist frequency, is more prone to aliasing than the GFX 100, with an MTF of about 0.35 at Nyquist. Both these numbers may be a bit high because of the high-contrast target, but I think the ratio should be approximately correct.

The Last Word – GFX 100 sharpening in Lightroom

Looking at these curves, it seems like the decreased pixel-level sharpness of the GFX 100 compared to the GFX 50S is not as significant as what are usually considered moderate sharpness moves in Lr or ACR.

The Last Word – Fuji GFX 100 vs 50S sharpness with 3D subject

The color balance is different between the two images. I’ll put that down to Adobe’s support of the GFX 100 currently being preliminary.

The GFX 100 image doesn’t look unequivocally sharper, but it is more detailed and smoother. But there are other systematic differences:

  • There is far less false color in the GFX 100 image.

  • The blue/purple fringing in the GFX 50R image that appeared to be LoCA isn’t present in the GFX 100 image, indicating that it was a false color artifact.

The Last Word – Fuji GFX 100, 50R aliasing differences

  • The GFX 100 can record finer detail before it starts to alias (It would be amazing if this were not true).

  • The aliasing is most striking with the GFX 50r

  • The false color is worse with the GFX 50R

The Last Word –Visual comparisons of Fuji GFX 100 14 and 16 bit raw precision

There are some small differences in the noise pattern, but they fade into utter insignificance when compared to the horizontal banding the comes from the OSPDAF system. If you eliminate the banding in post production, the differences might conceivably be worth worrying about, but they are tiny.

The Last Word – Visual comparisons of Fuji GFX 100 and GFX 50R shadow noise

My take: absent postproduction work to mitigate the OSPDAF banding of the GFX 100, and with no noise reduction, it has a usable dynamic range that is inferior to the GFX 50R. Because of the finer pitch, nonlinear noise reduction should be more effective with the GFX 100. I’ll test that in the next post.

The Last Word – Fujifilm GFX 50R and 100 shadow noise with nonlinear noise reduction

The GFX 100 image is smother, but traces of the PDAF banding that plagues the shadows with that camera remain.

The Last Word – Sensors outresolving lenses

There’s your answer. If you’re going to use diffraction, lens aberrations, and defocusing to create a strong enough low-pass filter that there’s no visible aliasing, your image is going to look really soft at the pixel level.

The Last Word – A visual look at GFX 100 focus bracketing step sizes

Say you’re doing focus bracketing. Decide how far out of focus is acceptable by picking a just-marginal image. set the step size to that or one unit less. If you’re doing stacking, decide how much softness the stacking program can manage, and pick that step size.

The Last Word – How fast is the GFX 100 electronic shutter?

14-bit That means it took the shutter 8.33*19.5 =  162 ms to make the trip. That’s about 1/6 of a second.

16-bit Now there are 42 bands. 8.33*42 = 350 ms, or about 1/3 of a second.

The Last Word – Quantifying the Fuji GFX 100 focus bracket step size

Regardless of the f-stop, the step size is that which produces about a 1 um diameter CoC. The camera is compensating for the f-stop to make your life easier.

The Last Word – A visual look at GFX 100 diffraction blur

The first image with no trace of aliasing is the f/16 one, although the aliasing is quite low in the f/11 image. Aliasing is eliminated with less overall blur than in the defocused examples in the earlier post, indicating that diffraction blur is more effective at countering aliasing than defocusing.

The Last Word – GFX 100 AF-S and AF-C accuracy with 110/2 lens

With the exception of shooting wide open or nearly so, we don’t lose much accuracy to get the improved speed in the GXF 100.

The Last Word – Averaging GFX 100 images

The random noise has diminished a lot, but the PDAF banding is even more apparent.

Note: I didn’t align the layers, and used EFCS shutter mode. There is some camera motion visible. Next time I try this, I’ll use ES shutter mode.

The Last Word – PDAF banding in GFX 100 in-camera JPEGs

You can still see the banding, just not in the darkest areas of the image. The in-camera JPEG crushes the blacks so hard that the banding is less apparent. It also employs heavier noise reduction.

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