An Idea of PC (Perspective Control)
In 1961, pioneers of Nippon Kogaku K.K. (Nikon Corporation) in those days gave birth to the world's first interchangeable tilt-shift lens for a SLR camera. The lens named "PC-NIKKOR" was released in July 1962 and, soon won popularity.
A desire of a lens designer of those days was to come true a tilt-shift function which is due technique of a large format camera by a maneuverable 35mm (135) films format SLR camera. I was surprised when I looked into the instruction manual of PC-NIKKOR 35mm f/3.5 which was originally issued upon release of the lens. In this manual, an interpretation of trial models and the history of development were explained as well as explanation and uses of the tilt-shift effect.
Having a read through the manual, you will be able to feel enthusiasm and abundant knowledge of the lens designer of those days for photography and cameras. Roughly three kinds of mechanism (lens barrel) had been manufactured by way of trial until the first PC-NIKKOR 35mm f/3.5 was completed.
Surprisingly, the first trial model was equipped with even a tilt mechanism. However, the tilt mechanism was abbreviated since they may have thought that depth of focus was sufficiently deep in a 135 format wide-angle lens different from a large format lens, so that the tilt mechanism was less frequently used. Thanks to their decision, a really compact, simple and handy lens had been completed.
In the case of PC-NIKKOR, I think mechanical (lens barrel) design was much more difficult than optical design.
I also think it is generally rare that a lens mechanism (lens barrel) designer, in comparison with a camera body designer, considering his troubles moves into the limelight. Because, in interchangeable lens design, it tends to be thought that a lens designer is an optical designer.
However, in the case of PC-NIKKOR took up this time, it is no exaggeration to say that the development of the lens depended only on the skill of a mechanical (lens barrel) designer. In the mechanical (lens barrel) design of the world's first PC-NIKKOR, marvelously original ideas were included abundantly to become easy mechanism for handling.
History of the lens
Nikon has always produced large format lenses. There are a number of employees who are familiar with a large format camera.
Time was about to change from a S type rangefinder camera to a F type SLR camera. In order to bring out the merit of a SLR camera to the full, the concept of PC-NIKKOR was born coincidentally with the development of Nikon F camera.
Now, let's go back to the history of development of PC-NIKKOR. The original PC-NIKKOR 35mm f/3.5 (composed of 6-group, 6-element) was released in July 1962.
Then, in May 1968, PC-NIKKOR 35mm f/2.8 (composed of 7-group, 8-element), which was newly designed for a large aperture, was released as generation change.
Later, in April 1976, (new) PC-NIKKOR 35mm f/2.8, which was revised its appearance, and, in November 1980, PC-Nikkor 35mm f/2.8, which was revised its lens barrel design, were put on the market successively.
On the other hand, in compliance with the wish for a wider angle of view, (new) PC-NIKKOR 28mm f/4 (composed of 8-group, 10-element) was released in July 1975. Then, PC-Nikkor 28mm f/3.5 (composed of 8-group, 9-element), which had a larger aperture of f/3.5, was released in February 1981 and now, after 22 years, it was continued to sell with revising its multicoating to SIC (Nikon Super Integrated Coating).
Moreover, in compliance with the wish for a medium telephoto PC lens, such as a large format Nikkor lens, suitable for shooting an object, PC Micro-Nikkor 85mm f/2.8D was developed and released in September 1999. As is called "Micro-NIKKOR", this lens not only has superb optical performance in close-up shooting, but also wins popularity in the field of commercial photography because this has an angle of view equivalent to that of an about 127.5mm lens in 135 films format when the lens is used in combination with a digital camera such as D1 series.
Pioneer's passion for PC-NIKKOR further grows and is continuously inherited to successors.
So, let's turn a spotlight on (new) PC-NIKKOR 28mm f/4.
The optical designer was Mr. MORI, Ikuo, introduced in Tale Nine. Optical design report was made in 1974. Originally Mr. MORI was a main optical designer of large format and middle format Nikkor lenses, and also had incomparable skill in optical design of wide-angle and super wide-angle lenses.
Classification of lenses into "a telephoto lens" or "a wide-angle lens" should not be determined in accordance with its focal length, but with its angle of view. You may easily understand this when you imagine a camera using a plurality of film formats such as a large format camera.
Usually, a 28mm lens for a 35mm films format SLR camera has an angle of view of about 74 degrees. On the other hand, PC-NIKKOR 28mm f/4 has a maximum angle of view of 90 degrees. Using its magnificent image circle, you may freely frame your subject, so that PC-NIKKOR makes it possible to correct distorted image.
Even though it is nothing more than a shift (tilt) lens, how much shift (tilt) amount is to be necessary for correcting distorted image ? Since there was no precedent in the world, nobody gave the answer. In order to determine the maximum shift amount of PC-NIKKOR, the know-how of a large format camera must have been necessary. In this respect, Mr. MORI was the most suitable person for the optical designer.
Lens performance and imaging characteristics cross-sectional view
Please look at the cross-sectional view. You may notice that (new) PC-NIKKOR 28mm f/4 is a typical retrofocus type lens. Although it has relatively fewer lens elements of 8-group, 9-element, you can see the design concept that arranging a positive lens to the first lens element, distortion (image distortion) is reduced as much as possible.
What are the imaging characteristics of PC-NIKKOR 28mm f/4 ? Let's take a look at how this lens performs from both aberration characteristics and actual shots.
When you look at aberration values, you may notice very small meridional coma and sagittal coma over the entire image field in the zero shift state. Accordingly, you can expect the lens to have high contrast and clear image rendition.
In the vicinity of the maximum shift state, it cannot be denied that imaging performance somewhat decreased by produced astigmatism and coma. However, it is inevitable in consideration of the magnificent image circle.
Moreover, lateral chromatic aberration is slightly large, but did not cause major problem in the actual shot.
Furthermore, the peripheral quantity of light is excellent and abundant.
In particular, it deserving special mention that the amount of distortion is exceptionally small. In spite of a wide-angle lens, this lens superbly corrects distortion as the maximum value of -2.6% within entire image circle having an angle of view of 90 degrees.
Here is Nikon's consideration for PC lens. To tell the truth, distortion is a natural enemy of PC lens. Because if image distortion is remained in PC lens for removing perspective distortion, the reason for existing the lens is to be reduced by half. The deformation produced by (image) distortion has not been able to be corrected by any possibility upon shooting until recent appearance of image processing software.
f/4, f/16, 1/125 sec., Y-48
Presto400, Ilford Multigrade paper
©2002 SATO, Haruo
f/4, f/16, 1/125 sec., Y-48
Presto400, Ilford Multigrade paper
©2002 SATO, Haruo
Please take a look at Examples 1 and 2. Example 1 is a picture showing that perspective distortion is corrected by the shift mechanism.
Example 2 shows that perspective distortion is maximized by using the shift mechanism inversely. Did you notice at a glance that these two example pictures were shot by lenses having the same focal length ? If there was no explanation, you would very likely believe that Example 1 was shot by a normal lens and Example 2 by a super wide-angle lens. I think it is fair to say that the skill of a large format camera that the pioneer was eager to realize by PC-NIKKOR is just this.
Then, what about the essential lens performance ? Please take a look at Examples 1 and 2. You may recognize sufficient sharpness and full gradation. According to my actual shots, it seems to me that this lens does not have priority on resolution, but on contrast. In actual shots, I obtained best optical performance upon stopping down from f/8 to f/11.
Mr. FUKINO as a "Waku-ya (Frame shopkeeper)"
We engineers sometimes call each other with putting a name of your technical field such as "XX-ya (so-and-so shopkeeper)". This name may be a kind of an engineer's dialect. So, we call each other like a nickname such that an optical designer like me is called a "KOUGAKU-ya (Optical shopkeeper)", a mechanical (lens barrel) designer is a "KANAMONO-ya (Hardware shopkeeper)" or a "WAKU-ya (Frame shopkeeper)", and an electric circuit designer is a "DENKI-ya (Electrical shopkeeper)".
Generally, "interchangeable lens design" may recall you optical design. However, optical design only is nothing but pie in the sky. Collaboration with a superior mechanical (lens barrel) designer and an electrical circuit designer can only permit to provide a product to be widely used by users. It is not too much to say that whether it is very handy or not as a tool is highly dependent on consideration and intelligence of a mechanical (lens barrel) designer.
Among Nikon's WAKU-ya (lens barrel designers), this time I introduce Mr. FUKINO, Kunihiro who has the longest career in this field. Mr. FUKINO having rich experience is relied on not only by lens barrel designers but also by optical designers like us. When an interesting idea is come to mind, or when getting into a scrape, it is always Mr. FUKINO to whom a designer asks for an advice.
Regarding PC-Nikkor Mr. FUKINO had a lot of ideas. The fruits of his effort are living in PC-Nikkor 28mm f/3.5 for reducing its weight and for improving operability and in PC Micro-Nikkor 85mm f/2.8D for improving a tilt mechanism and a preset aperture stop.
I admire his energy and unabated inquiring mind from day to day. Anyone who has been attending to only one work for many years has irreplaceable knowledge and insight, and is really reliable. There are still a lot of expert engineers in Nikon Corporation. I believe that this is the origin of a corporate culture and nature.