How do I calculate the diode parameters for reverse polarity protection?
For such a low allowable drop, you need a zero voltage drop diode. It can be done with a P-Channel enhancement mode MOSFET. E.g. a IRFD9120 is sufficient for up to 1A drain current.

(Use a multimeter and check how much current your camera draws. Check it with display on and zoom moving.)







simulate this circuit &ndash; Schematic created using CircuitLab