Charged particle beam apparatus comprising: an objective lens adapted for focussing a primary charged particle beam on a specimen plane, so that charged particles are emitted from the specimen with a spatial distribution; and a charged particle detector assembly for detecting a spatial distribution of charged particles, the charged particle detector assembly comprising: a particle detector, the particle detector having at least one particle sensitive region for detecting at least a portion of the spatial distribution of the charged particles and adapted for generating a two-dimensional optical signal which correlates to the detected spatial distribution, wherein the particle sensitive region is an essentially simply connected region; an image conduit having an input coupled to the particle sensitive region of the particle detector for transmitting the two-dimensional optical signal to at least one optical detector (46, 48); and a selecting means (50, 45, 56) adapted for selecting at least a portion of the two-dimensional optical signal, wherein the selecting means (50, 45, 56) is arranged between an output of the image conduit and the at least one optical detector (46, 48), and the selecting means (50, 45, 56) is a variable selecting means for variably selecting portions of the two-dimensional optical signal, and wherein the particle detector is arranged in front of the specimen with respect to a main propagation direction of the primary charged particle beam. an objective lens adapted for focussing a primary charged particle beam on a specimen plane, so that charged particles are emitted from the specimen with a spatial distribution; and a charged particle detector assembly for detecting a spatial distribution of charged particles, the charged particle detector assembly comprising: a particle detector, the particle detector having at least one particle sensitive region for detecting at least a portion of the spatial distribution of the charged particles and adapted for generating a two-dimensional optical signal which correlates to the detected spatial distribution, wherein the particle sensitive region is an essentially simply connected region; an image conduit having an input coupled to the particle sensitive region of the particle detector for transmitting the two-dimensional optical signal to at least one optical detector (46, 48); and a selecting means (50, 45, 56) adapted for selecting at least a portion of the two-dimensional optical signal, wherein the selecting means (50, 45, 56) is arranged between an output of the image conduit and the at least one optical detector (46, 48), and the selecting means (50, 45, 56) is a variable selecting means for variably selecting portions of the two-dimensional optical signal, and wherein the particle detector is arranged in front of the specimen with respect to a main propagation direction of the primary charged particle beam. a particle detector, the particle detector having at least one particle sensitive region for detecting at least a portion of the spatial distribution of the charged particles and adapted for generating a two-dimensional optical signal which correlates to the detected spatial distribution, wherein the particle sensitive region is an essentially simply connected region; an image conduit having an input coupled to the particle sensitive region of the particle detector for transmitting the two-dimensional optical signal to at least one optical detector (46, 48); and a selecting means (50, 45, 56) adapted for selecting at least a portion of the two-dimensional optical signal, wherein the selecting means (50, 45, 56) is arranged between an output of the image conduit and the at least one optical detector (46, 48), and the selecting means (50, 45, 56) is a variable selecting means for variably selecting portions of the two-dimensional optical signal, and wherein the particle detector is arranged in front of the specimen with respect to a main propagation direction of the primary charged particle beam.