There was a discussion thread discussing observable IQ difference between X1D and D850.
Answering that kind of question is a bit hard, because any comparison is easily getting an apples to oranges comparison. To get a valid comparison we need:
- Shoot the same subject
- In the same light
- use comparable lenses
- Develop identically
- Shoot tripod
- Be able to go back and repeat
DPReview published a good test of the Fuji GFX and include some comparisons with several 24x36 cameras.
Below is an image, developed in Lightroom with no sharpening or noise reduction and resized to 100 cm picture height at 180 PPI and identically sharpened in Focus Magic:
At that size, the GFX definitively has some advantage.
Let's look a bit at the sources of that advantage.
Pixels is what carry the informationLet's compare the vertical number of pixels on Hasselblad X1D and Nikon D850
X1D | 6296 | 14% advantage for the GFX |
Nikon D850 | 5512 | |
But, the quality of the pixels may also differ. One aspect of that is the fine detail contrast transferred, that is normally measured as MTF. Below is MTF data for the GFX and the Nikon D850:
A measure LP/PH (Line Pairs at Picture Height) MTF50 (at 50% transferred contrast).
X1D | 1915 | 19% advantage to X1D |
D850 | 1614 | |
A small note. MTF at Nyquist is 26% on the Nikon and 25% on the X1D. That means that both would do well with say 8000 vertical pixels, 85 MP on the X1D and 100 MP on the D850.
A usable measure of image sharpness is SQF, that has been proposed by Ed Granger of Kodak.
If we look at SQF for 100 cm picture height we would have:
It used to be said that it takes about 5 SQF points for a visible difference.
So, what I can see is that there is a material advantage to the GFX when comparing images between the GFX and Sony A7rII in DPReviews comparison.
Comparing MTF data between the GFX and the D850 there is a 19% advantage to the X1D.
Looking at the SQF data, there would not be a observable difference at 100 cm print size.
The image based comparison includes sharpening, while the MTF data have been calculated on unsharpened images. The MTF data gives a 19% advantage (in LP/PH) to the GFX over the D850.
Rules of thumbResolution and magnification are linear properties. A 44x33 mm sensor has 1.68 times the surface area of the 24x36 mm sensor, so that would yield a linear advantage 29%.
This discussion looks at image quality near centre. Looking at corners may be different.
Best regards
Erik