People do tend to go on about 2001, but it's on a list of movies where I have to say that it's revolutionary for its time. Without that caveat? The effects are in many places quite crude.
Indeed. Youtube Apollogist astrobrant2 made two excellent videos showing various mistakes and inconsistencies in
2001: A Space Odyssey:
(Part 1)
(Part 2)
Part 1 seems to have been taken down because of a DMCA complaint, and I can't find any mirrors. Astrobrant2 has been the victim of sustained (indeed, criminal) DMCA abuse by Jarrah White, and it can take a long time to restore videos that have been taken down improperly.
Neither of us had noticed most of these mistakes before, but you only have to look for them. Many are exactly the kinds of "anomalies" in lighting and relative object size that the Apollo deniers imagine in the Apollo photography. In
2001 they're real and often quite blatant. Ever since the movie first came out, my favorite "incoherence" has been the conference room scene, supposedly set on the moon. If they had walked like that on the real moon, their heads would bounce off the ceiling.
So why was everyone so impressed by
2001 at the time? I can think of several reasons:
1. It was so much better than anything before it, even if that isn't saying much.
2. Most of what passes for "science fiction" in TV and movies is actually fantasy set in space, e.g.,
Star Trek and
Star Wars. Clarke, an accomplished "hard" science fiction writer, actually
tried to adhere to known physics when possible. The
USS Enterprise and countless other fantasy spaceships simply handwave artificial gravity into existence. Kubrick and Clarke actually tried to simulate weightlessness. When they do implement artificial gravity, they do it in a physically plausible way.
3.
2001 came out in 1968, just before the first Apollo landing. We did not yet know just how inaccurate those thousands of paintings of imaginary lunar scenes really were.
4. In 1968 we didn't yet know how real astronauts would move inside a large spacecraft. The big fear was becoming stranded, unable to reach a handhold. So Kubrick and Clarke implemented what was then thought to be a good way to move in such a cabin: Velcro on shoe soles and walkways. But when the first large manned spacecraft, Skylab, was launched in 1973 astronauts quickly discovered how easy it was to get around. You just push yourself in whatever direction you want to go and grab something when you get there. How do you get to the center of a large open space without velocity, and how could you then cancel that velocity to become stranded without touching anything? It should have been obvious that stranding was a non-problem, but worrying about non-problems is a time-honored tradition in the space business. The problem is that you often won't know if something will be a problem or not until it happens, and then it's too late.
Every manned spacecraft cabin also has a substantial ventilation system to prevent hazardous bubbles of CO
2 from forming around astronauts, and that also tends to move things around.
So that scene of the flight attendant retrieving Dr. Floyd's pen is now just laughable. So is her full bathing cap. In the real universe, astronauts with long hair tie it down or just let it float. Of course, a cap neatly avoids having to simulate the behavior of long hair in weightlessness when you're filming a movie.
Everybody has now seen enough video from real spacecraft to
know what true weightlessness looks like and how real astronauts behave in it. Any serious space movie with a pretense of realism now has no choice but real weightlessness, either in an airplane (like
Apollo 13) or by actually going up there. Only the second option would make the astronauts themselves look right, where under sustained 0g fluid moves up in their bodies and into their faces. (I suppose you could simulate that on earth by hanging the actors upside down for a while before each scene.)
Thanks to old Apollo video, almost as many people know what real 1/6 g looks like, so again they're not likely to be fooled by anything but an airplane, and then you've got not only a limited duration but a limited volume. I suppose you could always construct a small vacuum chamber on an airplane, but that's getting pretty involved. Basically, faking lunar gravity in a movie is just so intractible that no one even tries. The fans generally understand and agree to suspend disbelief. Duncan Jones' "Moon" (2009) is a good recent example.
Regarding front projection, there's a very big giveaway in the "Dawn of Man" sequence at the beginning of "2001". A resting leopard is seen at twilight with glowing eyes. Cats, like many animals (but not humans) have a tapetum lucidum behind the retina to reflect light that would otherwise not be detected. We were seeing the reflection of Kubrick's front projector in the leopard's eyes. It was unintentional but the effect was so striking that Kubrick kept it.