Schmidt camera was used as fast astro-photograph, but it has a strong field curvature. Emulsion film can be fit the curvature, but digital camera cannot because CCD or CMOS is solid.
I just traced rays of Schmidt camera with a flattener, a singlet lens. Its spot diagram is very good. The flattener power is twice of the primary mirror, and its position is just 3mm away from the imager. This short distance may be a big problem for digital cameras, but only Starlight Xpress SXV-25MC can be used for this new Schmidt camera.
This camera is easy to be opened and could be attached a singlet lens directly on the cover glass of the CCD. This camera cooling system is not strong, so it would cause splitting the cover glass and the flattener lens if they were cemented.
D=250mm, f.l.=600mm, f/2.4
mail about Flat Schmidt Camera