purpose of the study was the determination of methods for the 
objective measurement of image quality which have a high degree 
of correlation with the subjective usefulness of the images. 
Subjective "usefulness" was characterized by a psychophysical 
scaling of the images, based upon subjective quality judgements. 
In order to make the subjective evaluations as close to 
operational practice as possible, two ground rules were adopted. 
First, the simulated aerial photography was made at typical scale 
and resolution on standard operational materials, and second, 
the examination of the image simulated actual photointerpretive 
practice as much as possible. 
Five objective measures were evaluated. They were; 4:1 
contrast resolution, 1.6:1 contrast resolution, edge slope, acu- 
tance and spectrum areas. 
The correlation analyses led to the selection of edge slope 
as the best objective measure of those investigated. The selection 
was based largely upon the fact that edge slope gave high correla- 
tion in every case, and in no case, exhibited significant spread 
function shape dependency. 
6.5 MTF Measurement on Infrared Lenses 
Hinebaugh of the U. S. Aerospace Guidance and Metrology 
reports82 on an MIF method of measuring infrared lenses in the 
eight to fourteen micro-meter wavelength region. Thermal imaging 
systems in this spectrum provide passive night vision devices 
looking only at the thermal radiation emitted by the objects 
being observed. Corresponding to the trend in development of 
such IR devices, there is more demand for good image evaluation 
techniques at these long wavelengths. The paper describes the 
techniques and reports MTF measurements made on an extremely 
fast (f/0.75) infrared lens. 
The collimator design was an off-axis spherical mirror with 
an aspheric mirror corrector, 1000? C blackbody with interference 
filters limited the radiance to the spectral requirements. A 
variable speed chopper modulated the energy to permit the use 
of synchronous detection techniques in measuring the signal for 
the detector. 
The alignment techniques are critical and time consuming. 
The autocollimating features of a thecdolite are used, aligning 
the reflected images generated by the surface of each lens element. 
When off-axis measurements are made, the nodal point is positioned 
over the axis of rotation. 
35