For a different view on the question discussed in this thread, see the November 2021 thread
Masking a Ground Glass for Cinema Aspect Ratios
See, in particular, the first post and then post #5 and following. The table attached to post #5 shows aspect ratio applied for the practical purpose of scaling.
I don't see the point of saying that the aspect ratio of a 4x5 sheet of film is 4:5 and of an 8x10 sheet is 8:10 unless one is just being descriptive. I think that it's more useful to express the aspect ratio at its most reduced. This makes clear the commonality of 4x5 and 8x10. I also prefer to express the long side first, which is invariably how it's done for cinema/video and computer displays. As far as I'm concerned, the aspect ratio of 5x4 and 10x8 is 1.25:1. I can do practical things with that ratio, starting with comparing these two film formats and their aspect ratio to others. In the thread above, see the table attached to post #5 and the photograph attached to post #8.
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