 On the other hand, the best (curved) image surface of the Schmidt is practically free from off-axis aberrations, hence clearly superior in quality to a best (flat) field in the Wright camera.Also, since the Wright camera requires twice as strong corrector to cancel spherical aberration of the mirror, its chromatic error is double that in a comparable Schmidt camera.Both, more strongly aspherized corrector and, especially, strongly aspherized fast mirror (into a rather unpopular type of aspheric shape) of the Wright are a fabrication disadvantage.