In layman's terms, how close would this be in quality to the original camera negative? CineCraft, what is it that you see in the screencaps that tells you that the source was an interpositive? I know a scan from the OCN is always the highest goal when possible, but how much of a drop-off in quality is there by scanning from an IP? I will add that the screencaps look pretty terrific to me and am just curious how they could theoretically look better.
In terms of quality, if the camera negative isn't available, then what you want is something struck from the camera negative, which is where this source comes from. And since it's a fine grain, that would suggest it's a master interpositive, which is what would've been used to make dupe negatives and answer prints. It's intended to be used for copying so the camera negative suffers less wear and tear, and hence is very high quality in terms of picture quality.
And because Ambersons did not perform well as the box office, it did not see as much circulation, and hence this master seems to have been in very good condition. Compared to a popular film like The Godfather, whose negative and masters were in bad shape from frequent printing.
IN terms of picture quality, it's hard for me to describe, since I've seen and handled films long enough from shooting myself that one just gets a sense for when one is seeing an original source image, or something that is a copy. In this case what i saw was very, very good, but just lacking a touch of that dynamic range that you'd get with a camera negative. Of course, Ambersons is a very contrasty film by design so this is less noticeable.
The other thing to bear in mind is that the quality of the presentation will vary from shot to shot, as this film was at times fairly effects heavy with mattes and optical printing work. The opening sequence, for example, is rather soft compared to the rest of the film, because of the vignetting that was inserted in post, which would mean that a new dupe negative would be produced, and hence that material is several copies away from the original, which takes away detail and enhances graininess. But again, it works in context since it's supposed to be a bit hazy and dreamlike.
