Select Enable to enable the electronic front-curtain shutter in Q, Qc, and Mup modes, eliminating blur caused by shutter motion. A mechanical shutter is used in other release modes.
The Electronic Front-Curtain Shutter
A type G, E, or D lens is recommended; select Disable if you notice lines or fog when shooting with other lenses. The fastest shutter speed and maximum ISO sensitivity available with the electronic front-curtain shutter are 1/2000 s and ISO 25600, respectively.