2K and 4K optical low pass filters

2K Optical Low Pass Filter for Sony F55
The 2K optical low pass filter is placed on top of the sensor.  
The original announcement about these filters can be found on Sony's F55 community forum, but the new filter makes it possible to have one camera capable of full-sensor 4K as well as full sensor 2K.  Many cameras resort to "windowing' the sensor by using a smaller portion of the sensor, which changes the effective field of view of the camera and makes what was formerly a wide angle lenses suddenly a narrower lens.  In order to use the entire sensor, it's necessary to change the optics.  The camera ships with a 4K optical low-pass filter that's optimized for 4K imagery, and recently Sony introduced an optional 2K optical low pass filter that's likewise optimized for 2K imagery.  There's some interesting technical reasons that Allistar Champman delves into, but importantly, there's an optical solution that's easy to swap in and out when changing the F55 from a 4K camera to a 2K camera.  Additionally, the 2K optical filter can lend a softer 4K image if desired.