With no crop factor, 50mm is pretty close to what's "in frame" for me, with my glasses, and 35mm is pretty close to what's "in frame" for my total field of vision. You'd have to defocus pretty hard to make a 35mm lens match what my uncorrected eyes actually see, though...

This conversion doesn't actually make any technical sense. Yes, you can calculate the field of view, but the depth of field, the angles of sight lines etc. are that of a 35mm lens.

For an intuitive way to visualize this: look at a few dolly zooms and think about what you are seeing in terms of geometry.