Quote Originally Posted by r.e. View Post
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.
1.25:1 doesn't easily help you if you looking to print. 4"x5" or 8"x10" or 16"x20" is more convenient to tell you the paper you need. All those measurements are 4x5 ratio times 1x, 2x and 4x.