見到另一個留言解釋多一點呢個現象,長知識
When the aperture has to close down to take a photo, a lens can shift the focus during the aperture closing. Sony and Nikon choose to mitigate this by focusing at the specified aperture. Canon chose to build more expensive lenses that does not shift focus during aperture closing which means using a poorly designed lens on Canon can result in slight mis-focuses while on the Sony/Nikon you will get in general not as good AF performance due to stopped down focus. It's just different solutions to a problem and neither methods are superior to each other, they're just different.