Hey guys, I've been set this problem sheet for optics and I haven't got a clue how to complete it, the course was really rushed and all of us have been left confused, so any help would be greatly appreciated. 1. A man is stranded. He needs assistance and his mobile battery is dead. How large does he need to write the letters 'Help!' in the saad for the team back at CTU to read from the images taken by the spy satellite 250km above him if its mirror is 2.5m in diameter, has a focal ratio of f/4, uses a filter centred at 500nm and works at the diffraction limit? (6 marks) Consider the physical size of the diffraction limited image at the focus assuming the angular magnification of the image is unity(?). If the telescope was limited by the physical size of each element of the charge-coupled device at the telescope focus, how much larger would he have to write the letters? (2 marks) 2. I'm assuming Rayleigh''s Criterion: theta min = 1.22 (lambda/D) is one to use. 3. Like I said we've tried many things and would just like to know how to tackle the problem. Thanks!