GREGOR: Optics redesign and updates from 2018–2020 Lucia Kleint, Thomas Berkefeld, Miguel Esteves, Thomas Sonner, Reiner Volkmer, Karin Gerber, Felix Krämer, Olivier Grassin and Svetlana Berdyugina A&A, 641 (2020) A27 Published online: 01 September 2020 DOI: 10.1051/0004-6361/202038208