Focus Lens

[Crv9]

So I decided to use platinum to buy the Madurai focus lens. I equipped to my brand new Warframe. (Note that I already have the Z lens equipped to my other frame) When I go to the back where the person is how do I choose which one to use? It says it's stilled locked. Is there a way to use it or did I waste 40 platinum? 

Edited May 7, 2016 by Crv9

[spacerocks]

You need 50k focus rep to unlock that Focus tree.

[Wopel]

You equip the lense then you need to farm the affinity for that particular school to unlock the ability. The first time was "free" due to it being a quest reward.