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detectable contrast it would provide a reasonable basis 
for comparing the relative merit of lenses in practically 
useful terms. A similar conversion could be made for 
3-bar targets, or any other target currently used for 
resolving power measurements. For general use and stand 
ardization this would have the advantage of avoiding any 
break with previous practice and supplementing the limit 
ing figure with a graph of contrast versus size. 
On the other hand, it might be considered best to 
provide only the MTF or OTF curves and leave the inter 
pretation to the user. Thus lenses would be compared in 
a relative way without reference to any special condition 
of use. The dangers of this should be sufficiently obvious 
from what has been said. 
10. Conclusions 
1. The MTF is a valuable tool for the anal 
ysis of aerial photographic systems, in 
assessing lens designs, and research 
studies generally. 
2. It may not be possible to achieve great 
accuracy in applying the MTF to the photo 
graphic process, because of non-linearities. 
However, for many applications in design and 
analysis the concept of an emulsion MTF is 
often useful. 
3. Effective MTF’s may be applied to certain 
stages or components, e.g. windows, filters, 
air turbulence, provided that the non 
general nature of such MTF’s is recognized. 
4. The MTF and OTF find their most natural 
application in the optical imaging com 
ponents of the photo-optical system, e.g. 
camera and enlarger lenses, microscopes 
etc. The OTF is a sensitive tool for meas 
uring lens performance, potentially superior 
to photographic resolving power in precision 
and accuracy. However, its full value will 
not be realised without considerable impro 
vement in the accuracy of present measuring 
techniques. 
5. The MTF does not, by itself, give more than 
a general indication of the value of a lens 
for practical photography because 
(a) without consideration of the emulsion 
no sound conclusions can be drawn.