How do I swipe in the opposite direction (find the antipodal point)?

I'm sure this isn't as hard as I'm making myself think it is, but currently a common complaint with my game is that the user can swipe the screen to see around them, but it feels wrong because the camera tracks the finger whereas it should swipe in the opposite direction.

So I'm trying to work out how to lerp the camera to the opposite spot with the player as the central point.

I'm either typing in the wrong thing, or there is a serious lack of documentation on this (I'm leaning to the first assumption), but I can't for the life of me find a formula or documentation to help me with this.

thanks

Okay, this is what I've come up with using sin and cos. I can't for the life of me get it to follow at a perfect opposite position without having a second object that runs at a right angle to the first.

I'm sure there's a way to get rid of that go between shadow object, but I think I might be too stupid to work it out. I've tried all sorts of different combinations with no luck... I mean, this works, but it's not really ideal having an extra object in there.

Not sure why the event sheet image didn't show up in the previous post: