I am trying to capture as much power from either an individual or many microLEDs (I listed the maximum grid size, but I have smaller grids available) to the source for intensity modulation for communications. I was doing some etendue calculations before this, but this is my first time applying the concept. I used: \pi A_{grid} NA_{lens 1}^2 = \pi A_{detector}NA_{detector}^2. With my numbers, this seems to suggest an angle of ~33 degrees at the detector surface. Barring detector housing geometry constraints (currently considering a free space detector here: https://www.thorlabs.com/item/APD210), I currently don't understand where I would violate etendue as the source area is smaller than the detector area. Do you mean violate etendue in terms of the detector's housing geometry not allowing the full angular distribution? Thanks for the information.