The field curvature and axial chromatic aberration, 2 of 13 aberrations in an electron optical system, make the major contributions to the image blur of a SCALPEL projector. We first give a simple yet quantitative evaluation of the point spread function from the field curvature and chromatic aberration and show the merit of keeping a comparatively low field curvature. Then we describe two ways to reduce the field curvature in an electron projection system. One is to use an immersion magnetic doublet with a constant field along most of the optical column with opposite signs at two ends which are connected by a sharp field transition region. The other way is to use space charge foils. By putting a space charge foil with homogeneously distributed space charge density on either the object or image plane, we show the field curvature can be eliminated in principle without affecting any other aberrations.