At risk of incurring the wrath of the thread creep police.
What are the largest lens constructed for conventional cameras I.E not for use in U2 or Canberra PR9 or satellites.
I’ve heard that Nikon made a 3000mm prototype available to the army in Northern Ireland for trials and that Carl Zeiss made a 5000mm mirror for the East German border guards.
I’ve got an old Soligor 800mm f8 on pentax screw thread and an MTO 1000mm mirror with an adaptor to fit my Canon A-1.
Be lucky
David