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ASTROPHOTOGRAPHICAL EXAMINATION OF OBJECTIVE LENSES 
Abstract. 
In the introduction the faults of lenses for a centred optical system are 
exactly described and shown in diagramms for three types of objective lenses. 
In this manner the following faults are usually given in the literature: the 
spherical aberration, the deviation of the sine condition, the sagittal and tang 
ential curve of the field of the image and the degree of the distorsion. Some 
times, these data are also given in tables. But it must be noted, that all these 
statements cannot allow exact conclusions concerning the quality of the optics, 
as it was also said by W. Merte, a collaborator of Zeiss. Besides the above 
mentioned characterisation of the faults of an optical system, other scientists 
have given characteristic figures, which tell mainly something about the relation 
between the ideal and the real received image. But this classification has only 
summary value, without to have regard to the individual faults of the lenses. 
Because the judgment of the quality of an objective with the above said 
presentations suppose a lot of special knowledges, the author has made it one’s 
task, to illustrate the faults of the lenses in another rate, which make it 
possible to get very easy an opinion on the objective to be examined. As for 
testing objects for the photographs, stars are used, because these are ideal points 
like light sources. At these star photographs, a very accurate focusing of the 
objective is requested. The method of taking photographs of star stripes were 
found to be very convenient. These stripes are measured by mean of a photo 
electric photometer with which the stripe with the greatest density can be 
found easy. The density is a much better argument for finding the accurate 
focus as perhaps the measurement of the width of the stripe. A diagramm in 
which the density is plotted against the shift of the lense, let find very quickly 
the precise position of the focus with an accuracy of at least one promille of 
the focal length. Already from this diagramm one can have a view of the 
quality of the objective, because in the case of a good lense, the maximum of 
the received curve is fairly sharp. With the so focused optical system a star 
photograph of a longer exposure time is taken in the usual way. An enlarge 
ment of parts of this plate, in steps from 3 to 3 degrees, beginning in the center 
of the field, is now produced and the pictures are put side by side. In a large 
picture table the author gives samples of pictures of some types of objective 
lenses, on which all faults of the lenses can be seen and judged very well. If the 
star photographs are taken in two regions of the spectrum, it is possible to get 
a judgment on the chromatic faults of the so examined lense. At the end of 
his paper, the author proposes, to take these star photographs from only one 
star and to move the axis of the camera in steps of for instance 3 degrees. In 
this way it is possible to receive knowledge of the diminuation of the inten 
sity of the light against the edge of the field of view. 
TOPAR LENS 1:4/f = 210 mm for 18 X 18 cm AERIAL CAMERAS 
by Dr. Robert Richter, Zeiss-Opton, Oberkochen, Germany. 
This paper and the one titled “Latest News on Photogrammetric Instru 
ments in Germany” were furnished as one reprint for binding into the Archives. 
Both papers are bound, therefore, under Commission II material.