How to change SLR optical camera into digital camera

Both digital SLR cameras and mechanical film SLR cameras are optical cameras;

Film SLR and digital SLR only record photos in different ways, and the optical framing and lens part are the same;

Film SLR body can not be converted into digital SLR;

The large format camera can do this, because the back of the large format camera is universal, and you can use the film back or the digital back;

Some lenses used in film SLR can also be used in digital SLR. For example, Nikon AI-S series lenses can be used in Nikon digital SLR, because Nikon F bayonet is compatible. However, Canon EF bayonet is not compatible with film FD bayonet lens;

Some film lenses can be used in digital SLR or digital mirrorless cameras by modifying the bayonet or installing the adapter ring. For example, Canon FD bayonet lens can be used on Sony A7 body through adapter ring.