A Modified Schmidt optical system is designed for ordinary conditions of imaging. The ordinary conditions mean the imaging of wide field angle and chromatic light. Traditional Schmidt telescope has special properties of aberrations that spherical aberration is perfectly corrected but other aberrations are remained to some level. So, to meet the ordinary condition of imaging, Schmidt telescope has to be modified to correct other aberrations. The most dominant aberration among them is field curvature aberration. For the correction of field curvature, a field flattener is added to near the imaging plane of Traditional Schmidt telescope. The field flattener is consist of one doublet lens to correct the chromatic aberration arising from Schmidt plate and the field flattener itself. To determine the feature of optical system 3rd order Seidel aberration analysis is done and optimization procedure is followed from the analytic result. The performance of Modified Schmidt optical system designed by writer is near the resolution limit. So the distribution of chromatic imaging spot traced from on axis and off axis object is confined in Airy disc. The important specifications of designed Modified Schmidt optical system are F/NO = 2.0, half field angle β = 2.0˚, MTF 0.5 at 240 cycle / mm, etc.
