[Leica] artistic intention and lens performance

[Erwin Puts <imxputs@knoware.nl>]

The argument that one does not need to be concerned with or 
interested in lens quality when one makes photographs with a purely 
artistic intent is a bit shaky. There are two implications here. One 
says that if you cannot see any difference, it is of no importance. 
And the other is that scientific lens testing is irrelevant for 
practical photography.
Let us first give some definitions. What is meant by 'scientific' 
lens testing. We all know that most lenses reproduce a three 
dimensional object on a flat plane of some recording medium (emulsion 
or CCD). This reproduction is not accurate due to aberrations. So 
every image projected by a lens will be degraded when compared to the 
original. This level of degradation can be measured by several 
methods and when put in a mathematical manner, can be evaluated in a 
scientific way. Scientific here just means that there are some 
theoretical notions which are expressed numerically and can be 
rationally discussed. The image degradation is theoretically and 
empirically defined as a number of optical aberrations, which can be 
identified separately. (coma, distortion, chromatic shift etc). So it 
is possible to study any optical system in the way it will record an 
image over its full image field and a number of distances from object 
to film plane. And of course for several apertures as the aperture 
influences the level of degradation.  In the past astronomers 
designed lenses purely by trial and error and got good results. Since 
we have an optical theory (thanks to Seidel and Petzval) we have 
progressed rapidly.
Now we can describe any lens in its level of aberration content and 
this description tells us quite correctly how much image degradation 
we may expect, including aspects as flare.
The artistic image starts with a random pattern of color patches, 
grey tones and luminance differences. Strange as it may seem: any 
photograph consists of a pattern of luminance differences, and that 
is all. Our senses make sense of such a pattern, and such a pattern 
evokes emotions, conveys meaning and records information. Here we 
have the realm of cognitive psychology and in photography this is 
codified in the so-called 'language of photography'. Numerous books 
have as subject the question how to look at a photograph and see its 
meaning and beauty.
In my view it is evident that the luminance pattern is influenced by 
the recording capacity of the lens (or its aberration content). By 
inference the aberration content will influence the recording of this 
pattern and so its meaning will be different  depending on the level 
of image degradation. There is thus a strong relationship between the 
optical quality of a lens and its projected image on film: the 
luminance distribution.
If we see this relationship and will acknowledge its importance is a 
different story.  That we do not see it, does not mean that it does 
not exist! That is a classical fallacy.
So lens quality and quality differences are of the utmost importance 
to anyone who wishes to record information and by doing this in a 
manner that evokes a human response (s)he needs to know the 
relationship between image quality and the meaning of a photograph.
It is evidently true that you may wish to ignore this. A pinhole 
camera works without a lens and gives fine imagery. The justified 
attention to the sharpness/unsharpness borderline implies a clear 
relationship between image quality and meaning. This deserves further 
discussion, not by denying the scientific approach but by 
incorporating it in the artistic way of photography.

Erwin