It’s not so much how close the subject is to the cameras. It’s not even the backlighting coming from the window. That mainly causes a silhouette effect that blocks out the details on the camera side of the subject.
The main reason for subject blur when they move has to do with the frame rate of these cameras, which is about 25 frames per second (FPS). Very slow. The higher the frame rate, the less blur you get when something moves.
Today’s really good smartphones can shoot video at up to about 240 FPS, which will give you decent, sharp slo-mo for the average photographer. It smooths out the slo-mo and gets rid of the blur.
Different frame rates are suitable for different scenes. The faster the action you are shooting, the higher should be the frame rate. The higher the frame rate, the less blur you’ll get when things move.
This is a nice little video from The Slo Mo Guys that illustrates, albeit at much higher frame rates, what happens when you use higher frame rates.
Note: Yes, I’m late to the party, but it can’t be helped.
