A multi-beam apparatus for observing a sample with high resolution and high throughput and in flexibly varying observing conditions is proposed. The apparatus uses a movable collimating lens to flexibly vary the currents of the plural probe spots without influencing the intervals thereof, a new source-conversion unit to form the plural images of the single electron source and compensate off-axis aberrations of the plural probe spots with respect to observing conditions, and a pre-beamlet-forming means to reduce the strong Coulomb effect due to the primary-electron beam.

A multi-beam apparatus for observing a sample with high resolution and high throughput and in flexibly varying observing conditions is proposed. The apparatus uses a movable collimating lens to flexibly vary the currents of the plural probe spots without influencing the intervals thereof, a new source-conversion unit to form the plural images of the single electron source and compensate off-axis aberrations of the plural probe spots with respect to observing conditions, and a pre-beamlet-forming means to reduce the strong Coulomb effect due to the primary-electron beam.

A multi-electron-beam (MEB) imaging system may include a field curvature corrector for individually correcting electron beamlets for field curvature blur by individually addressing microlenses of the field curvature corrector. The field curvature corrector may include a conductive plate, wherein the conductive plate includes a plurality of holes arranged in a hexagonal array. The field curvature corrector may include a microlens array, wherein the microlens array includes a plurality of microlenses formed on an insulative plate, wherein the plurality of microlenses are arranged in a hexagonal pattern to match the hexagonal pattern of the holes of the conductive plate. The microlens array includes a plurality of power lines for individually addressing each of the microlenses of the microlens array.