Lowdown mentioned it, but clean tubes are a thing. I’m more tolerant than most of tubes with “peppering,” blems and FPN/Chickenwire pattern. When I’m trudging around outside I don’t see them, and I don’t inspect white walls at night for a living. FPN stands out more to me than specks or blems, and there’s no place for that on the sheet. Also, “Tiger Striping” can be a bit off-putting, and there’s no measurement for that either.
Because higher tube resolutions (91LP and even 105LP) are just starting to trickle into the consumer market, FOM numbers get massively skewed. You can now have a 3000 FOM tube with a low 30’s S/N, so keep an eye on that. The new 4um tubes (usually the P/N ends in “1702”) are the culprits here, but one interesting side benefit is increased DoF, which before I thought was due to optics alone, but turns out the tubes play a part in that. My 3800 FOM 91LP 1702 binos could read normal text at arms-length when focused at infinity. That was crazy cool.
I won a single SOF reject tube because EBI exceeded their new 3000 MIN FOM spec. It was 105LP and 42.6 S/N. Doing the maths, that’s 4473 FOM (ironically). It was bonkers expensive and I got an offer I couldn’t refuse ($16K for ONE tube), so like any good Capitalist I jumped on it.