--21--

25) Equation 25 26) Equation 25
27) Equation 25 28) Equation 25

Since the inclination Γ of the extended field of view depends on the inclination φ2 of the secondary, it will result lowest in the anastigmatic device and largest in all coma-free devices. In the last explained device with a spherical corrector-lens it reaches nearly its minimum value.

Generally can be stated: by the adjustable inclinations of the mirrors an the corrector even considerable amounts of deviation from the theoretical parameters of the Schiefspiegler can be fairly eliminated and the system been brought to full definition.

The author tried out in a twentyfive years labour, to give the astro- nomical mirror its theoretical definition with means accessible for an ATM. It has proved in hundreds of nights of visual and photographic observation with Schiefspiegler of the different devices and sizes from two to twelve inches aperture that this is possible. The lunar photographs, taken with the authors optical not yet finished 'big one', (fig. 7) a 12-inch constructed after the device described last, may show it. These results were gained under unfavourable climatic cir- cumstances(the authors observatory being on the house-roof inmidst a 20 000 - population town under 48° northern latitude) and with an unfinished primary, which suffers from a turned down edge and zonal defects, so that its aperture must be stopped down to 10". With an equally sized Schiefspiegler, the mirrors of which are accurate to 1/8 wave-length, the results can be considerably surpassed.