tgm1024 has an excellent answer to the first part of your question. Now addressing the second part of the question:
Originally Posted by JediFonger
...are you saying that digital capture is already capturing at 35mm resolution or not? hard to decipher.
Strictly speaking about spatial resolution -- we're already technologically well past 35mm quality already, as a civilization. Extreme case: Just look at NHK 8K sample video at the demos they've given, and you'll see something more closely resembling IMAX resolution rather than 35mm resolution.
We'll likely soon have 8K bayer cameras downconverted to 4K for today's Digital Cinema, practically maxing out the RGB bandwidth of 4K. It's already started: RED has 5K cameras already, There's the Sony F65 too, 6K resolution (some say 8K, but without controversy). These are already giving you oversampling for 4K too to use up more RGB bandwidth, it already starts to approximately resembles 4:4:4 more often than 4:2:2 in resolution tests (apples to oranges, I know, but, strictly speaking, in terms of equivalent chroma resolution, like a red/black resolution test pattern). A lot of the 5K oversamples I've seen, easily surpass 35mm resolution. Even IMAX downconverted to 4K still looks sharper than 35mm film. On today's 4K digital cinema projectors, oversampled bayer downconverts to 4K already surpass typical 35mm resolution. Throwing another monkey wrench: It depends on the variables. Plain multiplex print? Master 35mm reel? Print from an IMAX? The quality of the grey matter of the people creating the viewing material? Straight 4K-bayer-to-4K-projection may not always outperform pristine 35mm master reels (the type reserved for Mann's Chinese Theater, and other flagship theaters) or really good 35mm prints of an IMAX reel, but it already outperforms multiplex prints on common 35mm projectors (now mostly discontinued in North America). Even 2K digital projection is an observed resolution improvement over a worn print on a crappy multiplex projector. (let's ignore other dynamics for now -- e.g. dynamic range -- which is another ball of wax altogether).
Resolution-wise, I've seen great 1080p that greatly outperforms poor 35mm, and I've seen 35mm outperform poor 4K.
But on average, right now, we well past the technological point where digital resolution can made to easily outperform 35mm film resolution.
Most multiplex digital cinema projectors are just 2K. So some of what you thought was 4K is actually only 2K. And make sure, if you're watching a 4K projector at the theater, it's playing good 4K material rather than 2K. On those, those presentations definitely consistently surpass 35mm resolution (unless the multiplex has neglected the projector's maintenance -- as so often happens!). Example is the movie "Oblivion" which used zero film (good example of oversampling to almost max out 4K RGB bandwidth). It even resembles IMAX resolution more than than 35mm! A bit blurrier than true IMAX, but way sharper than 35mm. And we're not even yet at widespread true 8K bayer sensors for practically maxed-out RGB bandwidth.Edited by Mark Rejhon - 10/4/13 at 7:54pm