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SUPPLEMENTARY REMARKS 
TO THE 
PROGRESS REPORT 
OF THE 
WORKING GROUP ON IMAGE GEOMETRY 
l. Calibrated focal length 
  
The values for the calibrated focal lengths listed for calibration 6 
are the focal lengths associated with the so-called "unbalanced" radial 
symmetric distortion. The "balanced" values, obtained in this calibration 
by forcing an equal positive and negative area under the curve over the 
full camera format, are 152.147 mm for the RC8 and 152.069 mm for the RMK. 
These values are included in the referenced report as part of figure 
captions but were overlooked. 
2. Reference plane 
  
Calibration 6 used theimage plane as reference plane. The two 
calibrated focal lengths given above agree well with those for calibrations 
also using the image plane as reference, i.e. calibrations 4a, 5,7 and 8a. 
(See Table 1 on page 12). The somewhat larger value for Z, in Table 3, 
p.20, for calibration 6 may also have been caused by use of the reseau 
plane rather than the image plane as reference. 
3. Reference point 
  
The determination of the principal point of autocollimation is not 
possible in stellar calibrations. The values xp and yp given in Table 1, 
p. 12, for calibration 6 are the coordinates of the foot of the perpendicular 
from the lens to the image plane derived by a least squares fit to the 
reseau. Since the principal point of autocollimation is defined as the 
extension of the chief ray of the object bundle, which by definition is 
perpendicular to the reference plane, xp and yp are similar to the values 
obtained for the principal point of autocollimation in other calibrations. 
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