I appreciate the knowledge everyone is sharing but a few myths are being perpetuated in the process.
-Breathing: I've observed focus breathing when using a black oval disc on the back of a simple SLR lens (say a Nikon 50mm or an old Russian prime) that wasn't present when focusing the lens without it.
-Bad anamorfake: A lot of people testing anamorphic mods on YouTube are not finding their lenses' sweet spots, not keeping to a cinematic shutter speed/angle, not composing carefully, etc. That accounts for why some stuff looks bad, but as shown above, there is some amazing footage out there from cheap modded lenses.
-Bokeh: As I mentioned above, stretched bokeh is easily attained with a mod on the rear element. There's another dirt cheap (and beautiful) way to get the bokeh, breathing and other anamorphic characteristics but I won't share it just yet. You won't believe me until you see the images.
But back to the original questions. (How to get the anamorphic look is a settled matter for me down here in DIY land.)
What I was curious about was how some popular mainstream films appear to have been shot with, if not anamorphic lenses, at least some character-rich vintage glass--but actually used character-deficient spherical lenses like Master Primes. I'm thinking of films like THE RUNAWAYS, a Super 16 film blown up to anamorphic 35 that looks like it was shot on old Super Speeds or somesuch but actually used Master Primes.
No colorist in the world could have layered in the texture in that film's images (could they?). Which is why I wondered if some "character" was introduced somewhere in the blowup process...? The bokeh on that film remains round but the feathery texture and rolloff scream not-Master-Primes.