Why is 12mp better than 42mp for HD video?

<p>I am trying to decide between the Sony a7Rii (42mp) and the a7Sii (12mp). I can understand why the 12mp camera is better for very low light as the pixels are bigger, but why is it better for video? And if 12mp is sufficient why make cameras with a whole lot more of pixels?</p>

<p>I suppose it is harder to distil a video pixel out of 21 sensor pixels than out of 6? That's what the Firmware needs to do, to get just HD info out of a Sony. - Writing the entire captured information to something seems impossible since it is too much data and way too fast.<br>

I guess high MP cameras get made because some folks chase the dream of printing out stills way bigger than just at screen resolution.<br>

The A7R II is a capable device that does video on the side. - Keep in mind that it does less than 30min at once and also might overheat even earlier. On the plus side you'll get better AF according to the reviews I read. <br>

Are you really determined to deprive yourself of DOF by getting a FF camcorder?</p>

<p>The A7S II has an optical low pass filter which is used to limit the resolution of the lens. Too much detail at the sensor can cause aliasing which upsets the video encoding and produces unwanted artefacts.</p>