> a (D)SLR doesn't split light It actually does. When you're not taking a picture, the main mirror is down. But there is a translucent part of the main mirror

> a (D)SLR doesn't split light It actually does. When you're not taking a picture, the main mirror is down. But there is a translucent part of the main mirror that goes to a secondary mirror that goes to the autofocus sensor below. https://keyassets.timeincuk.net/inspirewp/live/wp-content/uploads/sites/12/2011/07/Focusing_explained.jpg https://keyassets.timeincuk.net/inspirewp/live/wp-content/up... ; https://www.amateurphotographer.co.uk/technique/how-focusing-works-16250 https://www.amateurphotographer.co.uk/technique/how-focusing... ; https://alison.com/course/1326/resource/file/resource_200-1497623822678657349.pdf#page=5 https://alison.com/course/1326/resource/file/resource_200-14... Moreover, there are camera designs with a fixed mirror that always splits between the main sensor and AF sensor (but not viewfinder): https://en.wikipedia.org/wiki/Sony_SLT_camera https://en.wikipedia.org/wiki/Sony_SLT_camera