Challenges of 100 Megapixels in 35mm Format?
Related: diffraction, digital sensor, oversampling, true-color sensor or image
Are we going to see a ~100-megapixel sensor in the 35mm format? Very likely, but whether this year or next is unclear. And the win is going to be a lot smaller than you might think, barring some better technology.
- The 43.8 X 33mm sensor in the Fujifilm GFX100S/100 delivers 11648 X 8736 =101.76MP images.
- Images from the Sony A1 are 8640 X 5760 = 49.8MP.
Supposing we got a 36.0mm sensor width having 11648 image pixels, the same as the GFX100S. That means 90.5-megapixels in the 3:2 aspect ratio. For all practical purposes this is the "same". As in horizontal resolving power.
Awesome, right? Maybe not so much: such a sensor would mean a 1.348X linear increase in resolving power with 2.8-micron pixels. That’s getting really tiny. Can lenses handle that? Some can but even the best are going to struggle, particularly off-center. And focus shift and field curvature and plain 'ol focusing errors are going to make even the slightest mistake stick out like a sore thumb.
But wait, it’s even more fun, even if you do everything right with a super high grade lens.
Diffraction
With pixels roughly 1.4X smaller, diffraction dulling for fine details will kick in a stop early eg f/5.6 instead of f/8, while f/8 will look as soft as f/11 does now, and f/11 will be a blurry like f/16 does now (on the GFX100S and/or Sony A7R IV).
Depth of field
In terms of sharp detail relative to the resolving power of the sensor, you also lose a stop. Put another way, you’ll need f/8 to get the same detail capture per pixel as f/5.6. But... see the diffraction thing above! So you had better learn to focus stack! And that’s a hassle at f/5.6 (1.4X as many frames as f/8), so call it f/8.
How much more?
The 90MP sensor noted above vs today’s 50MP sensor is likely to net you a practical gain of ~33% gain in resolved detail—if you do everything right with the very best lens. In other words, little more than the Sony A7R IV can already deliver! Indeed, oversampling might be more of a benefit than more detail.
The True-Color solution
Camera companies understand all the stuff above, but they might still “go for it” for marketing purposes and because some image quality improvements do accrue.
A superior solution but one that might be years in coming would be a 50-megapixel true-color sensor. For example you’d have the 8640 X 5760 pixel count of the Sony A1 (50 megapixels) but with true RGB color at each pixel. Which gets away from the ever-tinier pixels. The resolved detail would be consistently higher and with better textural detail, because no demosaicing is needed.
The true-color sensor is the only serious contender for improving image quality forward in the future. More pixels will only kick the can half-way across the intersection but the bus of diffraction and dump truck of DoF will run over it.
And yet we see that Sigma is finding their true-color sensor project very challenging in the full-frame format; it’s not even clear it can be made commercially viable. We might need some new quantum dot sensor.
