The more powerful the better and makes sure the lens are UV coated (ie filter out UV light).
There's a very easy way to disprove the FET magical bendy light/ perspective. Just get on the radio, get out a shipping map and talk to the ship over horizon for a position. When you sail, you know the distance you have sailed, so you know the distances between various ports. If the world were flat those distances every sailor knows so well, can't be correct. It's the simplest of proof and something proved every single days by the thousands of vessles that cross the oceans. And the most concrete evidence in that is the amount of fuel used. No bendy light or illusionary perpsective theories can argue with that. Fuel consumption is directly proportional to the actual distance and speed travelled. That's why FETs stuggle so hard to produce a working map. I'm impossible to do.