Simon Firsht is a cinematographer who has worked on shooting behind-the-scenes Blu-ray/DVD footage for movies like Wonder Woman and Justice League. Apparently he also helped out on some of the reshoots that Joss Whedon did on Justice League.
Firsht released a five minute reel of his recent work on YouTube over the weekend. Around the 2:32 mark in the video above, we see Jesse Eisenberg as Lex Luthor against a green screen. The clapper behind him reveals that Firsht was working the camera and that Joss Whedon was the director. It appears to be dated September 23, 2017 as well.
It’s already been confirmed that Zack Snyder shot the Lex Luthor/Deathstroke scene before he dropped out, so Whedon likely just changed some of Luthor’s dialogue during the reshoots. Many of Snyder’s original scenes were changed during reshoots. The most obvious that come to mind are Barry Allen talking to Bruce Wayne in his apartment about brunch, and Aquaman talking to Bruce Wayne in the water in Iceland.
Eisenberg said in a recent interview that none of his Justice League scenes were cut from the movie.