and iii scanning devices are one galvanomirror 1 and one rotary polygon mirror table 1 shows the types of lenses 2 4 6 8 and 33 used for the above three cases i iii table 1______________________________________caselens i ii iii ______________________________________2 f arcsin u03b8 f arc sin u03b8 f arc sin u03b8 f arc sin u03b8 lens lens lens lens4 f arcsin u03b8 f arc sin u03b8 lens f u03b8 lens lens f u03b8 lens6 f arcsin u03b8 34 f arc sin u03b8 34 lens lens8 f arcsin u03b8 f arc sin u03b8 f arc sin u03b8 f arc sin u03b8 lens lens lens lens33 f arcsin u03b8 f arc sin u03b8 f arc sin u03b8 f arc sin u03b8 lens lens lens lens______________________________________ since the optical system shown in fig2 is essentially equivalent to that shown in fig3 an analysis of lens characteristic is made in the same manner as above only for the scanning optical system shown in fig2 the results are as follows iv the scanning device is only one designated by 11 which is a galvanomirror and v the scanning device is only one designated by 11 which is a rotary mirror lenses 12 16 and 33 used for the case iv are all to be f arc sin u03b8 lens and lenses 12 16 and 33 used for the case v are all to be f u03b8 lens as for the scanning optical system shown in fig4 the following analysis is made vi the scanning device is only one which is a rotary polygon mirror 31 vii two scanning devices are used which are one rotary polygon.