Thanks for the article, John.
fwiw:
in addition to longer ER allowing stray light betwixt eye & lens, have noted that sitting in a tree/elevated stand with a clear sky overhead as opposed to a blind with just the barrel protruding and the scope's objective lens inside, definitely impacts the low light "performance."
Also, a matted blue barrel reflect less light back up to the objective lens than a SS barrel.
Found this comparing a S&B Summit with 4" of ER & a Leupold to a short 3.15" ER Euro. The Euro gave a considerably "richer" low light view due to the shorter ER and additionally it was sitting over a blued barrel. Switching the S&B & Lupes off to a matte blued rifle and wearing a cap over the ocular lens brought low light performance right up to par...:)
