Refer to the Wiki for more information: Focus
Focus is a new system added to Warframe in Update 18.0. It is unlocked by completing The Second Dream quest and is associated with the Affinity system. Focus can only be generated on equipment which is modified with a Focus Lens from one of the five available schools of Madurai, Vazarin, Naramon, Unairu, and Zenurik. A standard Focus Lens will convert 1.25% Affinity to Focus and a Greater Lens will convert 1.75% of Affinity to Focus, but only on Rank 30 equipment. Focus Lenses cultivate excess Affinity which would otherwise go to waste.
Convergence is an even newer mechanic which will multiply all Focus gained by 6x for 45 seconds. Convergence shares similar spawn placement with enemies and can have anywhere between 30 to 300 seconds downtime after the buff expires.
Focus is subject to a flat daily cap of 100,000 which is shared by all five schools.
It is recommended to install a Focus Lens on your Warframe as well as the weapon you plan to use to get the most kills due to the way affinity naturally splits on kills. Kills made by your Warframe will generate 100% Affinity for your Warframe whereas kills made by your weapon will generate 50% Affinity for your weapon and 50% Affinity for your Warframe.
Each Focus tree comes with an active skill which runs on a timer. You can empower this skill and gain additional effects by earning Focus and using it to expand your school’s skill tree. The timer can be decreased or increased pending the active nodes selected in the skill tree. The rank of a given skill does not increase the activation cooldown period.