Yeah the thing with STM's background plates that they used for the soptic process was that they shot it in 35 mill, which is what they were shooting Reeve in as well. In process photography, as well as photochemical bluescreen, you want to shoot the background plates on a larger format then you are shooting the forground images on the Front screen stage. The reason is that the grain structre is 1:1 now, and is therefore visible in the projected image. Also, because it was 1:1, you had a fuzzier image. You want to shoot the background image when using Front Screen in either Vistavision or 65 mill, which is at least three times bigger than the 35 mill area, and therefore the grain is not noticable when projected shooting with 35 mill. Think of making a xerox of an image at the same size. The Xerox is a little bit fuzzier. But if you make a Xerox, but shrink down the images when making the copy, it is now as sharp as the original is. What happend was, in those days, the studios had gotten rid of their 65 mill equipment, or parted out their cameras 10 to 15 years before for 2 reasons:
1. They got rid of their internal camera departments, and where renting through vendors like Panavision and Otton Nemenz, etc.
2. No one was shooting in 65 anymore due to cost.
Disney, which came up with the Vista Vision format (35 mill camera with mag turned on its side to double the up and down area, and double the side to side area, giving a area 4 times the size of 4 perf 35 mill) had dismantled their camera departments as well, and also gotten rid of a lot of their cameras. Most of them where in pieces in junk piles in camera shops around Hollywood. When ILM was setting up in the old Van Nys warehouse for the first Star Wars, they bought most of the old Vistavision cameras in parts from those shops and put them togethere themselves. Then, when Star Wars became a hit, and SPFX film were being green lighted, and EFX guys from Star Wars were putting togethter their own EFX houses, they snapped up what was left. Any other Vista Vision cameras that you could find, even in pieces, were now a fortune.
When Superman was shooting, they were in the middle of this, and when they started shooting, or even planning the Zoptic efx aproach, especially since they where shooting in England, and the Wescam system they were shooting the background plates where only set up to house panavision 35 and Arri 35 mill cameras, nothing was set up for Vista Vision at that time. They started shooting EFX stuff right when all this came out and they now realized that the system they were using was not the right thing, but they could not have known at the time. So they were stuck shooting the backgroudn plates with the same 35 mill stock and cameras that they were shooting the process work with, and the grain showed up. By the time 2 started reshooting, there were companies making vistavision cameras, and you could rent them as well, so they now had them available. Wescam had also modified their mounts to accept both vistavision and 65 mill cameras.
So that is the story with the grain in STM.
They also didn't do a good job of color correcting some of the background plates in STM too. The screen used in the Front projection and Zoptic process is made of thousands of tiny glass beads. You know the road sighns where the letters light up from your head lights at night. That lettering is the same material. Those glas beads reflect back the images greener than the original projected images is. What you had to do was time the image with more pink that would counteract that, and when projected back to the camera from the screen, be color timed correctly in the shooting camera to the original color the plate was supposed to look. There are a bunch of plates where they mis color timed the plates, or the timing was off enough to notice. Again, the labs where ready for this problem and those things were fixed when 2 Was being shot.