F-Stop
The camera was initially adjusted with an aperture (F-Stop) to compensate for the bright reflection of the sunlight on the moon's surface. When totality occurs, the camera is manually adjusted to open the aperture to allow more light, allowing the viewer to see the deep red color. After totality, when the sunlight reflection initially reappears again on the moon's surface, the camera needs to be adjusted again otherwise the view will be washed out. Our human eyes will auto compensate much quicker than a manually adjusted camera aperture.
Thanks for the time lapse video,
Thank you catdlr for the explanation !