Image Quality
While astigmatism remains present in the Wright camera, it combines with the mirror's Petzval field curvature to result in a flat best image surface. In effect, the only monochromatic fourth order (wavefront) aberration of the Wright camera is relatively strong astigmatism.
In terms of the wavefront error, the flat-field P–V errors are identical in both, Schmidt and Wright camera, given by W=h2/16DF3 (h being the height in the image plane, D the aperture diameter and F the focal ratio number).
However, while the off-axis error in the flat-field Schmidt results from defocus, in the Wright camera it is caused by astigmatism. Since the RMS/P–V error ratio is smaller by a factor of 0.51/2 for astigmatism, the actual quality flat-field radius in the latter is larger by a factor of 1.4.
On the other hand, (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. On the plus side, the Wright camera is only about half as long as an equivalent diameter Schmidt. Also, since the corrector in Wright's arrangement nearly coincides with the image plane, it can support the film/detector assembly, clearing the optical path from supporting vanes.
Read more about this topic: Wright Camera
Famous quotes containing the words image and/or quality:
“As good almost kill a man as kill a good book; who kills a man kills a reasonable creature, God’s image; but he who destroys a good book, kills reason itself, kills the image of God, as it were in the eye.”
—John Milton (1608–1674)
“Although good early childhood programs can benefit all children, they are not a quick fix for all of society’s ills—from crime in the streets to adolescent pregnancy, from school failure to unemployment. We must emphasize that good quality early childhood programs can help change the social and educational outcomes for many children, but they are not a panacea; they cannot ameliorate the effects of all harmful social and psychological environments.”
—Barbara Bowman (20th century)