We use Optical Character Recognition (OCR) during our scanning and processing workflow to make the content of each page searchable. You can view the automatically generated text below as well as copy and paste individual pieces of text to quote in your own work.
Text recognition is never 100% accurate. Many parts of the scanned page may not be reflected in the OCR text output, including: images, page layout, certain fonts or handwriting.
94
KAPRELIAN
July
radius, it can have a more favorable Petzval sum, and it has a small fraction of the spherical aberration. There is a complete absence of chromatic aberration in the front-surface reflector and by placing the entrance pupil at the center of curvature of a spherical reflector, coma, astigmatism, and distortion can be reduced to zero. Reduction of spherical' aberration and appropriate flattening of the field are the principal goals in the utilization of mirrors as photographic objectives. The first large-aperture reflecting system of extended field is that accredited to Schmidt,3233 Fig. 4a, which utilizes a spherical reflector and an aspheric corrector plate. It is generally well corrected except
SCHMIDT P/0.7
SONNEFELD f/0.5
HOUGHTON f/0.6 BOUWERS f/0.9
Fig. 4 — Reflecting objectives.
for curvature of field. The Schmidt system has had numerous applications and has been modified in a variety of ways even though the image falls inconveniently between the mirror and the correcting plate and though the latter is not readily or inexpensively produced at present. A logical next step was the elimination of the aspheric correcting plate. This was done by Sonnefeld,34 Fig. 4b, who utilized a dispersing corrector comprising a positive and a negative element having spherical surfaces to correct the image formed by a Mangin mirror rather than by an ordinary front-surface spherical mirror to achieve an aperture of //O.5. Mangin-mirror arrangements of //0.9 and //0.6 apertures are described by Flugge,36 and Martin, Flugge, and Roll36 have utilized a Mangin mirror hi combination with refracting elements to produce a system of //0.8 for television projection without the use of aspheric surfaces. Houghton37 obtains an aperture of