>Again, the sensor size doesn't matter, what matters is the focal length.
Well, yes, but the two are obviously tightly linked if we're comparing a DSLR to a phone camera.
I'm going by the calculation in the 'Cameras' section of https://en.wikipedia.org/wiki/Airy_disk It explains why only the f-number is relevant. If you plug values for an iPhone into the 'x =' equation, you'll see that an iPhone camera is not really close to being limited by diffraction. The minimum separation distance at 500nm wavelength at f1.6 comes out to 976nm. Along an 8mm sensor dimension that's 8188 line pairs. Now sure, that's by the Rayleigh criterion, so you're not resolving 8188 perfectly sharp line pairs. But that's a still a good margin over the sensor resolution, and it's an open question how good sharpening algorithms can get.
I'm afraid that the radius, not the diameter. The diameter of the airy disk at f1.6 for 500nn is of 2 microns, and for a line pair you'd need double that, not a single, so a line pair would fit on 4 microns. Over an 8mm sensor that's 4000 lines, 2000 line pairs. Note that even here contrast is reduced by diffraction as we are operating from the first null. If you use the Rayleigh criterion and relax your standard for resolution you're at 4000 barely distinguishable line pairs. IIRC that would 4000LP at MTF15, so at MTF50 you might be at around 2500-2600?
And this is of course the very best you can do at 26mm equivalent focal lengths, if you want a tighter or wider shot your image quality degrades because once again the optics don't fit and you'll have to reduce your f number.
2000 line pairs in perfect conditions is quite low. Better is expected from cheap DSLR zoom lenses.
I think you are basically out by a factor of 4 by using the diameter instead of the radius and requiring line quads rather than line pairs. I believe the lp/mm value obtained is for ~9% MTF, so it's a fairly generous estimate of the available resolution, but not excessively so.
Regardless of the correct definition of lp/mm, the iPhone has plenty of room to increase the sensor resolution at f1.6. And phone cameras could certainly move to somewhat wider apertures and somewhat larger sensors.
Phone cameras are already at the limit of the space they can occupy. You would have to trade off the number of cameras.
As for the rest, lp/mm only makes sense at a given MTF rating. MTF50 is the standard. MTF9 is very, very, very generous. Incredibly so.
But anyways, sure, let's take 900lp/mm on the short edge for 4590lp/mm MTF9 - maybe I misremembered. A 5DSr with a real world zoom lens, the 24-70mm F2.8L, gets 7700lp/mm in the real world, and that's the MTF lens-sensor system, not just the lens. And that's not even close to the maximum possible resolution, nor to the maximum you can actually get in real life as you can. If you take the sharpest full-frame lens I know of whose MTF9 is limited to 400lp/mm because no testing apparatus was available that could go higher, the actual maximum is around 9600lp/mm. In any case, even the highest theoretical resolution of a phone is far lower than the practical resolutions of ILCs in use today, and is actually less than the sharpness of a 90$ lens on the very cheapest full-frame body you can find.
Indeed, take the Canon 50mm EF II, with an MTF50 yielding ~2000-2400lp/mm on the short edge of FF sensor. According to this source (https://www2.uned.es/personal/rosuna/resources/photography/D...), at around f/1.6 we should get around 420lp/mm, on the short edge that's 2142lp on the short edge, which is less than the cheapest EF lens in production right now. I don't know about you, but the best possible performance in theoretically perfect conditions being under the performance of the cheapest EF lens in the real world says something.
In real life, of course, the lens-sensor system will barely get close to the theoretically perfect result, and you will peak at the best possible result being around half the linear resolution of the cheapest production Canon lens.
Keep in mind, if you were to go for a larger sensor, you'd have to increase the focal length to compensate too. So 20% increase in sensor size length would need a 20% increase in focal length and at the same f number you'd need a 20% wider aperture too. And again, you'd be fixed at around 25mm FF eq. focal lengths, if you try more practical focal lengths like 50mm FF eq. you would see a drop in quality. They're already pretty much at their optical limits and have been for a while, actually f/1.6 isn't even the fastest phone lens - but those had smaller sensors still.
Well, yes, but the two are obviously tightly linked if we're comparing a DSLR to a phone camera.
I'm going by the calculation in the 'Cameras' section of https://en.wikipedia.org/wiki/Airy_disk It explains why only the f-number is relevant. If you plug values for an iPhone into the 'x =' equation, you'll see that an iPhone camera is not really close to being limited by diffraction. The minimum separation distance at 500nm wavelength at f1.6 comes out to 976nm. Along an 8mm sensor dimension that's 8188 line pairs. Now sure, that's by the Rayleigh criterion, so you're not resolving 8188 perfectly sharp line pairs. But that's a still a good margin over the sensor resolution, and it's an open question how good sharpening algorithms can get.