Archived posting to the Leica Users Group, 1999/11/09
[Author Prev] [Author Next] [Thread Prev] [Thread Next] [Author Index] [Topic Index] [Home] [Search]Erwin: I appreciate your comprehensive approach to testing lenses. They are wonderful and credible references for everyone to use as an element in selecting their lenses. The question that I have is, "Can the user tell the difference?" As an example: I enjoy my darkroom work and like the best equipment that I can justify. During the past year I have collected quite a few enlarger lenses and have limited my tests to side-by-side prints made at the same magnification. Agreed, this is not scientific. My goal is to reduce my enlarger lens inventory to one lens for 35mm and one for medium format. Yesterday I made four prints from the same negative and used a different lens for each print; Focotar 40mm f2.8, Focotar 50mm f4.5, El Nikkor 80mm F5.6 and El Nikkor 75mm f4. I printed each negative as close to "full frame 35" as possible (approx 6-1/4" x 9-1/2"). I used a Saunders 4500XL enlarger with a glass negative holder. I used Ilford Multigrade IV RC satin paper. Erwin, there has got to be a difference but damn if I can see much in the prints. I have spent over an hour with different loupes and magnifying glasses and the best that I can come up with is Focotar 40mm may have a bit more shadow detail. I can't confirm this but there may be a bit more information. The 80mm El Nikkor may be the closest to it. About 6 months ago I did the same test using a 50mm Rodagon, 80mm Rodagon, 50mm Apo Rodagon and the 50mm Focotar. The only one that I kept was the Focotar 50mm. In retrospect I should have kept the Apo Rodagon but I am not losing any sleep over it. Erwin, I have come to the conclusion that basically all of the lenses that I use are good to the extent that I use them. I am curious at to what magnification visual recognition of the quality differences would be. The prints that I made are approximately 40x. Also, my tests are not scientific enough to make a conclusion thus I must use your research as a reference. However, if I can't see it what difference does it make anyway? Personally, which enlarger lense(s) do you use? Thanks for your input and I certainly hope that you are feeling better now. Continued good health to you. Bob Bedwell << 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 >>