(210) 
— to speak not of focal distance but the principal distance in a metric 
camera; 
— to retain, unlike the rest, the test relative to the distribution of light 
only as a characterization test. To express the clarity of the camera 
by relating the illumination of the image to the brilliance of the object, 
without arbitrarily fixing at 100 the clarity on the axis of perfectly 
transparent lens with aperture F/0.5, so far removed from that of 
present day lenses used in aerial photography. 
Dr. L. E. Howlett: Before throwing the meeting open for general discus 
sion I should like to express on behalf of the Commission our thanks to the 
speakers whom we have just heard for the time and trouble which they have 
taken to prepare such thoughtful and helpful comments on the draft specifi 
cation. It is a matter of considerable encourage that all the speakers have ex 
pressed general agreement with the draft, and it is to be hoped that this is an 
augury that there will be a similar sentiment in the discussion which will now 
follow. The meeting is open for anyone to make comments. For the conven 
ience of the recording system I would ask each speaker to announce his name 
and country before making his remarks. 
Dr. I. C. Gardner: I am glad to see that such a high degree of agreement 
had been reached on the specification. However, I have a number of sugges 
tions for detailed changes in the specification which I wish to bring up for 
consideration at this time. These suggested changes follow: Section 1.3.2 should 
be changed to read “Line lengths are not less than five times line widths”. It is 
believed that there will be no significant difference in readings with lengths of 
five times and any greater length. A greater length is convenient if it is desired 
that test negatives be evaluated by means of a micro-densitometer. Referring to 
sections 1.3.2, 1.3.3, and 1.3.4. — When used with collimators as recommended 
the patterns photographed at different angular distances from the axis will 
show different spacings. It is the practice at the National Bureau of Standards 
to so distort the test targets for the individual collimators that they will appear 
of the same size on the negative. It is our recommendation that such a proce 
dure be made mandatory or at least optional (see Note to section 1.3.5, con 
cerning the annular target which sets forth a identical requirement). Section 
1.5.1 should be changed to read “The target should be placed at the focus of a 
collimator or at such a distance from the lens under test that the aberrations 
are substantially those of an infinitely distant target”. An advantage of this 
second option is that it does permit an arrangement by which the effect of 
veiling glare may be included. Section 1.5.3 — this paragraph seems unsatis 
factory and certainly not at all consistent with paragraph 1.1. If there is a con 
venient method for calculating reduction of resolving power with glare, it 
should be spelled out in the report. We know of no method of accomplishing 
this unless the resolving power as a function of contrast is determined, and this 
seems not to be contemplated in the present specification. Referring to sections 
3 and 4. — For measurements of veiling glare and image illumination, it seems 
unwise to insist that the measurements be made by photographic photometric 
methods. With suitable precaution both measurements may be made more con 
veniently by electronic methods.