Hufuage163 suggests a "Simple Approximation to Diffraction 
Limited MIF." With the quoted accuracy of +0.003, this should 
allow shortcuts in many analyses. 
Hufnage19^ also notes that the phase angle of OTF contains 
valuable information and is necessary for a proper evaluation 
of image quality. The absolute value of OTF must also be taken 
into account. His paper presents a mathematical method to account 
for phase in image-quality evaluation and he concludes that "For 
the broad class of linear measures of image quality ... only the 
real part of the optical transfer function ... contributes directly 
to quality. However, the entire complex OTF, including the phase 
transfer function must be known and used to determine the suitable 
coordinate system." A later study®’/ established a 70% confidence ( 
limit for MIF measurements, based on the use of phase. Tests 
showed that the basic assumption that "over the range of interest 
when the modulus does not have a very small value, the true transfer 
function is real with no imaginary component," was valid for typical 
edge gradient analysis data. 
A study by Scott?? shows that observers can just distinguish 
a 5% difference in the size of spread functions of grainless photographs 
of identical scenes and 10% for different photos. Further, the 
study showed that subjective judgment could be made quickly without 
detriment of performance. It was demonstrated that subjective 
image quality judgments made by professional photo interpreters 
agree well with photo interpreter performance. 
An experiment to investigate the use of MIF to diagnose 
camera faults was reported by Jones 66, He concludes: "The 
procedure produced diagnostic determinations which were in good 
agreement with the known values. The experiment demonstrated Ô 
that limited photo-optical system performance can be performed 
using MIF measurements... Diagnosis of MTF's must be used in 
conjunction with other sources of information such as flight 
instrumentation, atmospheric conditions, system design expectations, 
and laboratory measurements." 
A fifteen year old tutorial paper by Scott68 and his staff 
on MTFs discusses theory, optical design, random wave effects, 
film MIF, image motion MIFs and MIF instrumentation, and gives 
an excellent summary and an example of MTF of a tracking telescope. 
5.9.5 Fairchild Camera & Instrment Corp. 
At Fairchild Camera, MIF and OTF have found their primary 
applications in optical design and diagnostics. As an optical 
design tool evaluation, based on contrast and phase, calculations