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So I had a look at some of the more famous films featuring spacesuits that we know didn't (couldn't) use CGI -
2001: A Space Odyssey - it seems to have been done it the Roger Deakins' way, giving the viewer something else quite bright to look at in the reflection.
Alien (the first movie) seems to have been done the same way. In some later Alien movies, the visors were matted out as Mike suggests for many shots.
The trick seems (I don't know, I haven't even tried) to be to give the viewer some funky reflections to look at and keep the camera, camera person and crew as dark as possible.
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