Slits are placed in the ion path to define the positions and energies of the ions that strike the detector. In general, decreasing the slit widths increases the mass resolution but reduces the number of ions that are detected. Additional electrostatic lenses are commonly used to shape and deflect the ion beam to optimize peak shape and maximize ion beam transmission from the source to the detector. JEOL uses octapole and quadrupole focusing lenses to simplify the ion optical design. Collision chambers in the first field-free region (just after the ion source) and second field-free region (just after the magnet and before the electric sector) are used to induce ions to fragment in collision-induced-dissociation experiments (MS/MS).