JPL wrote:
And here is the exact discussion about this between Chris and me in another topic. I hope this will save my reputation in this discussion
ChrisT wrote:
That might explain why EVERY current Nikon Entry-Level body is 24mp, but it doesn't explain why they backed it down to 20mp on the D500 and D7500, nor why the new D850 is 46mp ... or why Canon has embraced 50mp for their 5D S and 5D S R ...
It's all about marketing, I guess ...
Me:
I guess so.
But still an interesting subject. When we think about lenses there are not many that will do more than 30 megapixels according to DXO. (I have no idea if they are accurate or not) and most modern lenses do less then 20 megapixels, even on cameras with 30-40 megapixels sensors. And if it is true that old glass was worse then modern then we could assume that film resolution was limited by lenses with someting less than 20 megapixels and in many cases far less. However putting top end modern glass on film cameras and a high resolution film in the camera could give different results. So probably there is no fixed number here.
And here is the exact discussion about this betwee... (
show quote)
The response of "I guess so" to the statement that "It's all about marketing" did not help, that's for sure.
First, it is not the case that 35mm lenses are not capable of resolving greater than 20mp.
Discernable resolution is SIGNIFICANTLY greater, much greater than even the current mega-MP bodies. Resolution vs contrast is a continuum; it's what is represented by MTF curves. By convention, an MTF of 50% is used to define the limit of perceived image sharpness, but MTF levels as low as 2-5% are distinguishable, and an MTF of 9% corresponds with the Rayleigh diffraction limit. Note that film ratings usually went beyond 30% MTF, typically with twice the resolution of the 50% MTF level.
So, even if you just consider 50% MTF as defining your resolution limit, there are several lenses that exceed that limit. And, the 50% MTF is an arbitrary cutoff over a continuum that extends well beyond that limit, easily by as much as a factor of 2 in lines of resolution, and a factor of 4 in number of pixels.
Second, resolution is dependent on a number of factors, including aberrations, noise, dynamic range. Some of these are lens dependent, some sensor/body dependent. This is the basis for the DXOMark measurement of perceptual megapixels, P-Mpix.
Consider the following P-Mpix ratings for the Nikon AF-S NIKKOR 50mm f/1.8G on the following Nikon bodies:
Nikon D500 (20mp) 13
Nikon D7100 (24mp) 14
Nikon D5 (20mp) 15
Nikon D750 (24mp) 17
Nikon D810 (36mp) 22
P-Mpix increases with pixel density for same sensor, and with sensor size. The relationship is approximately proportional, but might be subject to deminishing returns with increasing pixel density. However, there is no indication in these results that a higher full frame pixel count won't result in an increase in perceived sharpness. The diffraction limit will eventually make increased pixel density of insignificant value, but the increase to 46 or 50 mp still produces an increase in image quality. If it's not proportional, then that indicates that we might be approaching a limit.
Note that the 50mm lens I chose because it's been tested on most Nikon bodies. But it is not the sharpest lens in the tool shed. So consider the Nikon D810. There are lenses that test up to 35 P-Mpix (the Carl Zeiss Apo Planar T* Otus 85mm F14 ZF.2 Nikon). That lens is going to rock on the D850. Nikon lenses that test high on the D810 are
Nikon AF-S Nikkor 200mm f/2G ED VR II - 33 P-Mpix
Nikon AF-S Nikkor 400mm F2.8G ED VR - 33 P-Mpix
Nikon AF-S Nikkor 300mm f/2.8G ED VR II - 32 P-Mpix
Nikon AF-S Nikkor 85mm f/1.4G - 30 P-Mpix
Nikon AF-S Nikkor 28mm f/1.8G - 28 P-Mpix
So, there are several lenses throught the focal length range that have resolutions close to the pixel count of the D810. These lenses are likely to produce significantly improved results with a higher pixel count body like the D850.
For full frame cameras, the increase in pixel count is likely to produce significant improvement with the best lenses, and even noticeable improvement with "simply good" lenses. If you are shooting with lower quality kit lenses, you might not see any improvement because you are at the limit on those lenses.
As far as Nikon backing down on the pixel density of their APS-C sensors; there are a number of factors to consider, such as noise, readout and processing speeds. The D5, D500 and D7500 are all ~21mp sensors, and feature fast readout speeds and burst modes. They might be using similar electronics; I don't know. But the ability to crank frames is going to be limited by pixel count.