186 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1949 
will be eliminated or avoided in time, but during the tests they caused 
some loss of light and appreciable loss of definition. Nevertheless, 
the test plates record stars and nebulae fully 1.5 magnitudes fainter 
than the extreme limit of the 100-inch reflector on Mount Wilson. 
The faintest star images, on the better plates, were, however, a little 
more than 1 inch in diameter, and, at the threshold, it was sometimes 
difficult to distinguish with certainty between stars and nebulae. 
Thus the 200-inch has registered already the full gain in light- 
gathering power corresponding to the size of the main mirror. The 
slight additional gain that may be expected with a clean, sensibly 
perfect mirror surface will be accounted for by the absence of a 
Newtonian flat and by the very transparent sky over Palomar. 
The greatest improvement in the future will be in definition, as 
indicated by the size of faint star images. Definition is very sensitive 
to the seeing, and, while the test plates approached the definition 
to be expected under average conditions, they indicated that the 
mirror is not yet in shape to operate at maximum efficiency on the 
rare nights of fine seeing. The trouble arises from the turned-up 
edge and can be eliminated by the retouching now in progress. The 
improved definition will be significant, particularly for distinguishing 
nebulae from stars at the threshold of long exposures. In the higher 
latitudes, the telescope records many more nebulae than stars. 
The turned-up edge was well known from Hartman tests, and its 
effects could be predicted with some confidence. The photographs 
were made primarily to confirm and record these effects. However, 
the first plates were so impressive that a set of full exposures was 
made to serve as a record of performance before the mirror was 
removed for retouching. About 60 photographs were assembled over 
the 3 months from January 26 to April 28, as opportunities arose 
during the normal program of adjustments. Of this number, perhaps 
half a dozen represent full exposures under average seeing conditions, 
and a like number show good performance with reduced apertures or 
with a Ross correcting lens for enlarging the usable field. Selections 
from the files are illustrated in plates 5 to 10, and comments on them 
are given below. The full aperture (200-inch) and Eastman 103a—O 
emulsions were used in all exposures except those to which special 
references are made in the comments. The scale of the original 
negatives is about 1 mm=12’’. 
Plate 5, NGC2261; R.A.=6"36"6, Decl. =+8°47’ (1950); Jan. 26, 
1949; 15 min. exposure, poor seeing; enlarged 34x. 
This plate shows the first of the photographs with the Hale tele- 
scope. It is recorded as PH—-1-H (i. e., Palomar, Hale, No. 1, followed 
by the initial of the observer). It was made under poor conditions 
as a preliminary test of the mechanical operations and procedures 
involved in direct photography at the prime focus. The trial was 
