So Stone, what you learned is just what I said. As you approach infinity, you're getting close to that published 282mm flange focal length,
depending on exactly how you measure things. And that has simply been rounded to 300mm for marketing purposes, something common with
lens manufacturers. Closer up, you'll need more bellows extension. It's still a standard dialyte design and not a telephoto in any sense. But it is a damn nice lens.