To minimize the effect of different lens' focusing speed, we test AF-active shutter lag with the lens already set to the correct focal distance.
The D850 still relies on contrast-detect AF in Live View mode, though, so AF speed will vary a lot depending on the lens being used, and that is why we typically don't measure Live View full AF ...
light will reduce in speed as it travels through, causing it to change direction. Ray diagrams can be used to show the path light takes when it is refracted. Lenses are usually made from glass or ...