Hi, I thought I would weigh in on the whole 8.3 million pixels UHD standard.
Those arguing that the standard does not guaranty a sharp image are correct. From a practical standpoint, there are, of course multiple factors, including the quality of the lens, design of the lightpath, and more.
But, it primarily comes down to how big each pixel is, relative to the screen. 4K UHD DLP projectors with their 2716x1528 pixel structures (before pixels shifting), have pixels that are basically twice the area in size of a true 4K sized pixel, such as found with any Sony 4K projector. No way a 4K UHD pixel shifter can resolve to adjacent vertical lines, each 1/3840th of the width of the image. Make the first line blue, the second yellow, and you'll get mostly white with some blue fringe on one side, yellow on the other. Wit a true 4K you'll have two fully distinct lines, one blue, one yellow - no white.
Now so far, the only UHD projectors not true 4K are the new DLPs, but there's nothing, in theory, stopping Epson, for example, from devising a way to take the LS10500 (or LS10000) and pixel shift multiple times, hitting the screen 4 times, vs the DLP's 2 times. That would take the Epson from 4.15 megapixels to 8.3 and would make it 4K UHD.
Technically, since the standard does not seem to specify anything but the 8.3 million, one could even take a projector that's only got 720p panels, not even Blu-ray, and use pixel shifting to hit the screen 9x per frame. That too gets you 8.3 million pixels but each pixel would be roughly the size of a baseball compared to a true 4K projector's pixels the size of a golf ball.
Bottom line: Some projectors are sharper than others for various reasons (a quality single chip DLP that's 1080p will normally be sharper than a 3 chip LCD or LCoS since there's no three images to align.
I've found that the 4K UHD's I'm reviewing now, are definitely upon close inspection, sharper than the LS10500 or 5040UB, but the difference is slight, and not likely to be noticed (especially considering all the other processing today's projectors do,
if you are sitting, say 12 feet back from a 100" screen. (I'm assuming we're feeding them 4K content.)
I wrote a FauxK vs 4K article that covers this and more on my site, for those that want a bit more info, but my comments above address much of what's in the article. -art
"reviewing is fun, but watching The Fifth Element for the 500th time..."