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Bob Newman on his plea for small, light and fast lenses, even at the expense of corner sharpness
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The new breed of mirrorless cameras seems to come with enormous lenses, which is strange because part of the manifesto for mirrorless is that it allows for lenses with a short back-focus, thus making them smaller. The clue to the bloat in the lenses is in their specifications. These new lenses are exceptionally sharp wide open, right to the edge of the frame. In order to gain this desirable characteristic, the design of these lenses is much more complex than those we are used to with traditional SLRs. The Nikon 50mm f/1.8S for the new Z system boasts 12 elements. By contrast, the 50mm f/1.8G for the F-mount system has but seven, and that is complex for an f/1.8 standard lens.
Element number
The lens that made Nikon’s (or Nippon Kogaku, as it was then called) reputation was another fast standard lens, the Nikkor- H.C 5cm f/2.0. For the first 30 years or so of Nikkor lenses, the letter suffix after the name told us how many elements the lens had. ‘H’ stands for ‘six’ from the ancient Greek
Hexa. The ‘C’ designates it as a coated lens. This lens is derived from the classic Zeiss-Sonnar design, but it is not a straightforward copy.
Saburo Murakami, who designed all the early Nikkors, had different priorities from the German designers. Lens design is always a compromise, between size, cost and the various parameters of performance. By the standards of the day, a six- element lens was already towards the limits of technology, and would provide the peak of available performance. The real question was where the peak should be located. German practice was to aim for a spread of sharpness across the whole field of view, which meant compromising the sharpness in the centre.
Mr Murakami’s preference was to maximise centre sharpness even if the corners were a little less sharp. His reasoning was that the main subject was usually in the centre of the frame and in a fast lens, the corners and edges were generally rendered out of focus by the shallow depth of field.
Adopting Nikkor lenses
The story continues. In 1950 a photographer for the American magazine Life was stationed in Tokyo. The photographer, David Douglas Duncan, was working with a Japanese photographer who was using the newly available Nikkor lenses. Duncan was highly impressed with the results that these lenses produced, and ended up buying a complete set of the Nikkor lenses for his Leica, preferring them to the Leitz lenses. The story at the time was that the Nikkors were ‘better’ than the German lenses, but it was just that they made different compromises, and ones that suited normal photography better. When Duncan was later posted to cover the Korean War, other American press photographers discovered the Nikkor lenses, and they quickly became a preference among the US press corps.
Returning to the present day, it seems that the fashion has come back to the old German practice of wanting edge-to-edge sharpness wide open. Nowadays the compromise is not made with centre sharpness; it is made with size, weight and cost. But I think there was a lot of sense in Mr Murakami’s reasoning. Indeed, the subject generally is in the middle of the frame, and yes, the shallow depth of field wide open does render the corners blurred in normal use. So please, camera manufacturers, may we have some small, light and fast options, even if it does mean compromising on corner sharpness a little.