This is the 31st in a series of posts on the Fujifilm GFX-50S. The series starts here.
Since the GFX came out, there has been much ‘net discussion as to whether there are any quality improvements over the best full frame (FF) cameras with the best glass. Those discussions usually ignore the fact that the best FF glass of normal to long focal length works just fine on the GFX at aspect ratios of 4:5 or squarer. Nevertheless, it seems like a comparison of the Fuji 63mm f/2.8 lens on the GFX to the Otus 55 mm f/1.4 on the Sony a7RII might be instructive.
So that’s what I’m going to do today.
Sorta. I’m doing a very limited comparison. On-axis only, and for three parameters: resolution, longitudinal chromatic aberration (LoCA), and focus shift.
I’m using a variant of the protocol described here. The subject distance was 6 feet, which is about as far back as I can get with these lenses on these cameras. I tested at the lenses best apertures, which in the case of the Otus are f/2.8 through f/5.6, and in the case of the Fuji 63 are one stop down from there. That’s convenient, since because of the larger sensor, the equivalent f-stops on the Fuji are one stop down from a given f-stop on a FF camera. I lost a fight with MTF Mapper, and am only able to show you the red and green raw channels today. The blue ones are AWOL, and I don’t know why at the moment.
At the widest apertures tested:
The right side of the screen has the camera closer to the subject than the left. First off, note that the depth of field (DOF) of the two camera/lens combinations is about the same. You can see that the Fuji lens on the GFX is sharper than the Otus on the a7RII. We have already seen that the Otus on the GFX is only marginally sharper in the middle than the Fuji 63; that’s because both lenses can lay down details in the center of the image that the sensor can’t pick up. Also not, surprisingly, that the LoCA is about the same for both lenses. That’s because we can’t wee the blue channel here. We have seen that the blue channel in the Fuji 63 has about the shift of the red channel, while the blue channel in the Otus is pretty much on top of the green channel.
Stopping both lenses down a stop:
The Fuji is marginally sharper.
At the narrowest stops tested:
Looking at focus shift:
The focus shift on the Fuji lens is worse. Best to focus the 63 at the taking aperture. But that’s true of the Otus, too, just to a lesser degree.
My conclusion from this test is that the differences in central image quality between the two camera systems is small enough to be unimportant in normal photography. When you think about the price difference between the Otus and the Fuji 63, that’s a bit surprising. We have seen elsewhere that there is little difference between the photographic dynamic range of the two cameras. And, of course, the Otus has qualities that this test does not address.
But, as I pointed out above, the Otus is quite happy on the GFX, if you crop to 4:5 or squarer.