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  6. Tale 18 : AF Zoom-Micro Nikkor 70-180mm f/4.5-5.6D ED

World's first AF Zoom-Micro Lens Tale 18 : AF Zoom-Micro Nikkor 70-180mm f/4.5-5.6D ED

In this Tale Eighteen, I introduce an epoch-making lens, AF Zoom-Micro Nikkor 70-180mm f/4.5-5.6D ED that has successfully been completed to develop a micro lens into a zoom-micro lens.

1. Micro Lens' Trend toward Zoom-Micro Lens

Since a decade ago, I think, flower photography has gained latent popularity. Owing to this boom or not, micro-lenses have been selling well. In famous places for flowers or mountains, I frequently met people who took flower photographs with micro lenses. When I think of those days that I started taking photographs 30 years ago when micro lenses were exclusive for professionals, I feel I am living in a completely different age. As a result of increasing accuracy of auto-exposure (AE) and auto-focusing (AF), close-up photography may have become close to us.

However, a close-up photograph is by no means easy. I believe those who had an experience to take flower photographs know very well that in close-up photographs, camera should firmly be fixed on a tripod upon shooting in order to prevent camera shake and to compose strictly. If you use a tripod, however, you have to move your camera together with the tripod rightward and leftward or forward and backward whenever you want to change composition a little, or to change magnification of the subject, so it is a really nuisance. In close-up photographs, minute change in an angle produces considerable change in composition. Although you may get used to the change in horizontal direction, the magnification of the subject drastically changes with minute change in forward or backward direction, so it has been a really troublesome and difficult work for even a familiar lens.

Furthermore, in a field photograph, you are not always allowed to set your tripod at any position. You may often come across such case that you cannot draw back from or approach your subject because of a fence. So you are compelled to shoot with leaning over the fence holding the camera by your hands risking camera shake or give up shooting. A lens designer had been taking this to heart, "A zoom lens is essential for close-up photography."

Although designing a zoom-micro lens started like this, hurdles to be cleared were very high.

Optical performance was the first priority. So long as it was a micro lens, it must have a maximum magnification at least x1/2. This means this lens has to secure optical performance over more than 5 times wider range of magnification than ordinary lenses. Moreover, since this lens was a zoom lens, it was necessary to secure optical performance over entire focal length range. Over entire focal length range and entire focusing range, correction of aberration must have been carried out on both of these two aspects, only one of which was quite hard. On the other hand, the size and handling were also important. Since a zoom-micro lens was designed for using on site, it was out of question for the lens to be bulky and heavy even if it had excellent optical performance. Furthermore, if the focusing point varied upon zooming in a close-up focusing range, the lens cannot have been called as a zoom-micro lens.

Then, the development started from basic studies such that which specification permitted the lens to become compact, or to be handled easily, so that a lot of lenses were designed to decide the specification, 70-180mm f/4.5-5.6, with discussing the dimension and mechanical structure of the lens barrel. After deciding the specification, degree of the design performance had been polished by improving various aspects such as the number of lens elements, balance between the weight and optical performance of the lens, and adoption of ED (Extra Dispersion) lens.

After two years from the start of the lens design the lens was completed through two kinds of trial lenses.

2. Lens Configuration

Fig. 1
Cross sectional View of AF Zoom-Micro
Nikkor 70-180mm f/4.5-5.6D ED

As shown in Fig. 1, the zoom-micro lens has a lens configuration of a four-lens-group composed of negative, positive, negative and positive lens groups. Zooming from a wide-angle state to a telephoto state is carried out by moving the third and fourth lens groups approaching with each other. Focusing to a close object is carried out by moving the first lens group forward.

In a recent compact telephoto zoom lens, a zoom lens whose total length varies upon zooming becomes the main steam. However, when the position of the first lens group varies upon zooming, working distance and the focusing position varies in the close-up focusing range, so it is not so easy to handle. Accordingly, the lens has the configuration that the positions of the first and second lens groups do not change upon zooming so that the working distance is constant. The most prominent characteristic of the lens is that a negative lens group composed of five lens elements is arranged at the first lens group, so that the sharpness of the image from infinity to close-up focusing range is secured by this focusing lens group having compound structure. To put it shortly, the first and second lens groups play the part of a micro lens and the third and fourth lens groups a zoom lens, so by combining these two parts two functions of a zoom lens and a micro lens exist together. In addition, the construction of the lens barrel can be simplified by separating the focusing part and the zooming part, so that it cannot be neglected that it contributes to compactness and light weight of the lens.

By adopting an ED lens, chromatic aberration is excellently corrected, a sharp image can be obtained over entire zooming and focusing ranges, and distortion, an inevitable accompaniment of a zoom lens, is satisfactory corrected. When you shoot a subject extremely sensitive to distortion, a better result can be expected by shooting with using from the wide-angle end to an intermediate focal length.

3. Lens performance and imaging characteristics

Nikon F5,
AF Zoom-Micro Nikkor
70-180mm f/4.5-5.6D ED,
Aperture: full open,
Shutter Speed: auto
UV TREBI 100,
(shot in the telephoto end state, 180mm)
©2003/2004 OHSHITA, Kouichi

Let's take a look at how this lens performs with reference to Examples.

This lens gives so pretty images with providing good color reproduction and sharp but gentle imaging characteristic. In spite of the number of lens elements, the clearness of color is superb reproducing rich color even in backlighting because Nikon Super Integrated Coating is applied on each lens surface. Example 1 is a photograph of a pansy shot at close-up focusing range in a telephoto end state with a full open aperture. Despite of backlight condition, it gives excellent color reproduction without producing flare. Although you may pay stronger attention to defocused image in close-up photographs than in ordinary photographs, you may provably notice that it delivers so gentle defocused images.

In flower photographs, a micro lens having the focal length about 100mm used to be recommended. This is based on the fact that the shortest focal length of a lens that does not produce deformation in the image of the subject is about 90mm. However, when you use it in the field where camera position is restricted, a lens having longer focal length is easier to handle. Accordingly, this lens capable of shooting close-up photographs over entire focal length range from 70mm to 180mm is really ideal lens for flower photographs.

Nikon F5,
AF Zoom-Micro Nikkor 70-180mm
f/4.5-5.6D ED,
Aperture: full open, Shutter Speed: auto
UV TREBI 100,
(shot in the wide-angle end state, 70mm)
©2003/2004 OHSHITA, Kouichi

Of cause, this lens has high optical performance as a zoom lens as well as a micro lens. Example 2 is a photograph shot at close-up focusing range in a wide-angle end state with a full open aperture. In candid photographs like this, it is convenient that the wide-angle end of a zoom lens is 70mm.

Although this lens is frequently used at full open aperture since it is not fast, optical performance of this lens is excellent to be used even at full open aperture without anxiety. Moreover, since the lens does not vary its performance significantly with the aperture value, the focal length, or the focusing range, so that it is very easy to handle. Actually, whenever I shoot candid photographs with this lens attached to a Nikon F5, I can shoot smartly from distant landscape to close-ups of a small subject, so that I have an illusion that I can shoot any subject by this lens only. This sounds like a slight exaggeration, but if you add a wide-angle lens to it, you can cope with various shooting scenes. Although it may not be an appropriate word to explain a lens, this lens can be a productive lens capable of coping with most of scenes with minimal materials and labor.

[Zoom-Micro Lens Is Unexpectedly Fast]

If you hear f-number is 4.5-5.6, you may get impression that the lens is slow. However, you may provably not wish the lens were faster while actually shooting flower photograph with the zoom-micro lens. In close-up range, although you often stop down at about f/5.6 in order to secure depth of field, the real trick is an exposure increase factor.

In these days when AE has become popular, it is being forgotten that a lens has a characteristic that the lens gradually becomes slow upon focusing at close subject. Exposure increase factor shows the manner of becoming slow. In an all-element-focusing lens, exposure increase factor is two at magnification x1/2, and four at magnification x1. In other words, even if a lens has the f-number of f/2.8, when you focus at magnification x1, exposure increase factor becomes four, it means two steps stopping down, so the effective f-number becomes f/5.6. On the other hand, in Zoom-Micro lens, exposure increase factor is always one, it means the lens does not become slow. The following table shows effective f-number of Zoom-Micro lens comparing with other AF Micro lenses. Although the speed difference is more than one step at infinity, the speed difference becomes smaller to be about 2/3 steps at magnification x1/3, which is frequently used for close-up photographs. Accordingly, Zoom-Micro lens is unexpectedly fast in close-up range.

Table 1: Effective f-number of Micro Lenses
AF Micro
60mm F2.8D
AF Micro
105mm F2.8D
AF Micro
200mm F4D ED
AF Zoom-Micro 70-180mm F4.5-5.6D ED
70
mm
85
mm
105
mm
135
mm
180
mm
Infinity
2.8
2.8
4.0
4.5
4.5
5.0
5.3
5.6
1/4x
3.2
3.3
4.2
4.5
4.5
5.0
5.3
5.6
1/3.2x
3.5
3.5
4.5
4.5
4.5
5.0
5.3
5.6
1/2x
4.0
3.8
4.8
-
-
-
5.3
5.6
1/1.32x
4.5
4.2
5.0
-
-
-
-
5.6
1x
5.0
5.0
5.3
-
-
-
-
-

Note

This issue first appeared in "NIKKOR Club Quarterly" magazine; No. 184 (2003-03-31), published by the NIKKOR Club, and was revised for Nikon's webpage.
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