Is 70mm really necessary? Wouldn't it work with 35mm too? [duplicate]

Question

So I just came back from Dunkirk, seen in IMAX, 70mm version.

I was digging around the internet with my question but only found religious answers (it's just better, can't describe it, you must see it), rather than technical.

So I just considered these statements, which are hopefully correct:

• IMAX is screening films in 2K resolution
• According to IMAX, 35mm film has a digital equivalent of 6000 lines of horizontal resolution (6K), while 70mm film has the equivalent of 18,000 lines of digital resolution (more like 12,000 in reality).

=> 35mm seems to be more than enough for IMAX screen, why 70mm then?

I'm familiar with the DSLR world. Full frame cameras are better than APS-C, because the sensor captures more light, the camera performs better especially in bad lighting conditions. So for example you don't have to use so high ISO and have less noise and stuff like that. I did some simple tests (nothing exact, just going out with both FX and APS-C camera) and I would say that with good lighting (like on a sunny day), the difference in output photos is almost non-existent.

Back to my question. My thoughts are that:

1. 70mm is more about being commercially interesting.
2. The main difference in IMAX is the aspect ratio
3. Probably it gives the director (cameraman) some more space on what to do as the sensor is bigger and therefore captures more light. Some shots would probably look worst on 35mm.

Still not sure about: If they did shoot it on 35mm (even crop it to keep the IMAX aspect ratio), then screen it in IMAX on the same screen, would it look that much different?

edit: The question What exactly is 70mm print and why does anyone care? is different. It just asks what 70mm is. My question is more about whether 70mm makes any difference in comparison to 35mm given screen sizes and the fact that 35mm is already more than enough to capture resolutions needed for big screens such as IMAX.

Answer 1

Number 3 is the big point. Yes, a full-frame camera and an APS-C camera both take pictures with a high signal-to-noise ratio on a sunny day in good light. That's not when and where most stuff is filmed. A lot of stuff is filmed during the golden hour, the blue hour (or magic hour), and indoors at various times of day. A 70mm piece of film collects much more light than a 35mm piece of film, which leads to a better signal-to-noise ratio in low light, and the ability to project on a larger screen without loss of resolution. If projected on a large curved screen like IMAX often is, you can also get more of a feeling of being in the scene as it covers a wider field of view of your vision. The combination of the wider field of view and better resolution can have a psychological effect that leads to a greater feeling of immersion in the scene than with a traditional print and traditional projection. Keep in mind that in addition to the film and screen size, IMAX theaters also have a really good sound system that adds to the effect, too.

I found an interesting discussion on recreating the IMAX feeling in your own home theater, and the implication seems to be that the field of view is really important, as is the sound reproduction.