1- The dual challenge of achieving high performance within a compact body. The solution: Fixed-type lens.
- The X100 was originally conceived as a slim and compact camera for users to take with them wherever they go. When we first began considering the lens design, we examined the many possibilities from a variety of perspectives, for example, the aperture value and lens size in the case of a zoom lens and lens-body combinations in the case of an interchangeable lens system. As a result, we determined that a non-collapsible, single focal length lens was the ideal choice to meet our two goals of achieving the product concept and delivering the high level of quality demanded by professional users.
- Regarding the focal length, we considered the 135 equivalent of 24mm, 28mm, 35mm and 50mm. For each length, we evaluated the relationship between the F value and lens size, capability to satisfy user expectations, and the breadth of their application. We selected the 35mm lens as the best match for the camera concept.
2- Road to the F2 aperture value.
- Designing an F1.6 or F1.8 lens is not so difficult; however, in the case of a digital camera, even if an aperture larger than F2 is used, the light receiving elements on the sensor cannot effectively use the brighter portion of the incoming light because of low incident light gathering efficiency.
- Also by choosing an aperture of F2, it is possible to achieve a higher MTF* level when the aperture is closed to F4, F5.6, F8, etc. In most photographic situations, we envisage that users will often use an aperture that is 1 to 2 stops higher than F2. Therefore, in designing the lens, we put a priority on capturing superior quality photos with exceptional expression of detail in the aperture range of F4 to F5.6.
*MTF: Modulation Transfer Function is an index of the image formation performance of the lens. The value indicates the ability to reproduce contrast over a range of spatial frequencies.
3- The double-sided aspheric lens combined with high refractive index glass, results in optimum performance.
- The use of an aspheric lens increases the freedom in lens design; however, it does not necessarily lead to the development of a good lens. For the X100, spherical lens elements are used as much as possible, and one double-sided aspheric lens made by a glass moulding process has been adopted as the most effective element for delivering maximum performance.
- The X100 lens delivers performance in a compact body, and also boasts excellent results. The shape of the aspheric lens not only provides performance but also ease of manufacturing. As the other lens elements are spherical, a high level of design performance can be achieved when they are actually assembled in the product.
- High-refractive-index glass is used for all 4 convex lens elements. This is necessary to correct image field curvature and achieve optimum image quality.
4- 5.6mm back focus.
- In the case of the X100, the lens back focus, (the distance between the rear lens element and the sensor), is remarkably only 5.6mm. Incorporating the large-diameter rear lens element in the body and shaving tenths of millimeters from the lens elements and their integration, has also allowed us to retain a very slim and compact design.
- The sensor has been specially customised just for this lens. Unlike film, the sensors of most digital cameras require incoming light to strike the sensor surface at an angle that is as perpendicular to the sensor surface as possible. Because this is difficult to achieve with a slim lens, the positioning of the microlens on the sensor of the X100 has been customised to allow the capture of light rays with up to a 20° angle of incidence. Without this sensor customisation, it would be necessary to lengthen the size of the lens by 10mm.
5- Large-diameter internal lens structure – unnoticeable from the front.
- Exploiting the benefits of a fixed lens, the rear lens element is larger than the front lens element. By giving it a diameter of 27mm, which is about the same as the sensor's diagonal dimension of 28.4mm, ample light volume can be received in the edge areas of the sensor.
6- 9-blade aperture diaphragm and a high-performance lens shutter system.
- In order to capture images with a beautiful "bokeh" effect with the background softly out of focus, a 9-blade aperture diaphragm has been adopted for the X100.
- The 4-blade shutter achieves a maximum shutter speed of 1/4000s. Because the X100 uses a lens shutter system, the camera is capable of high-speed flash synchronisation.
7- An Integral ND filter allows the X100 to take full advantage of the power of F2.
- To enable shooting under very bright conditions with a maximum open aperture, an ND filter becomes indispensable.
- A sheet-type ND filter which can be switched on/off is built into the lens system. When switched off, the filter is retracted.
- The ND filter is the equivalent of an f-stop reduction of 3 stops or a reduction of light volume to about 1/8.
8- FOCUS; the only lens design software of its kind in the world! The essence of FUJINON lens design.
- Our unique lens design software FOCUS, (Fujinon Optical Class library & Utility System), is used in the design of Fujifilm lenses. The major difference from commercially available lens design software and FOCUS is that the software developer is able to work together with the lens designer. This enables rapid improvement of the software in response to the needs of the designer, which in turn contributes to higher quality lens design.
- In the initial stages of designing the X100 lens, we used a configuration of a gauss-type lens and the arrangement of the cemented-type lens near the image formation plane as the basis for our study. This configuration is especially responsive to bright F values and also has the benefit of superior close-up photography performance from the standpoint of low aberration variance. Unfortunately, the disadvantage of this type of lens is that the total length cannot be reduced, so further development was required.
- Keeping our development focused on the concept of a lens that achieves both high performance in a highly compact form, we cancelled our first design and went back to the drawing board. We then engaged in diverse experiments including the reversal of part of a lens element group, separation of the cemented-type concave-convex lens and other exercises, carefully evaluating each modification. This process was repeated many times eventuating in the production of a bespoke 6 group/8 element lens, a unique lens configuration completely different from a gauss-type lens.
9- One more challenge: 10cm macro performance!
- In order to expand the camera's scope of applications, a macro capability is essential. However, the adoption of a lens that has both a "bright" aperture value and slim size makes exceptional macro performance especially challenging.
- While adopting a focusing system of a fixed rear lens element group and an adjustable front lens element group, the lens has been designed to hinder the occurrence of "image plane error" when taking a macro shot. However, when shooting macro shots with an open aperture in the neighborhood of F2, spherical aberration tends to occur. It is therefore recommended that an aperture value of F4 is selected for macro applications.
10- All-new "Super EBC".
- In order to maintain high image quality with exceptional clarity, the lenses are treated with FUJINON's proprietary Super EBC.
- Of the 6 lens groups housed within the X100, 3 of the 12 faces,with the exception of cemented faces, are treated with conventional EBC. The other 9 faces are given a wide-band coating to prevent red ghosting from incident light rays, with a maximum of 9 layers of coating appropriately applied according to the requirements of the lens element.
11- Message to photographers from the X100 lens design team.The X100 lens is not just about focusing on a part of the scene and capturing only that area in sharp detail, it is about achieving beautiful quality that extends to the out-of-focus parts of the image. In designing this lens, we paid attention to the way the lens renders out-of-focus points of light and especially the beauty of the background "bokeh" effect. You could say that the X100 lens enables you to effortlessly achieve high image quality. With this lens, I want to make the most of its superior image quality with low distortion and high resolution to attain stunning landscape photos.
Takashi Suzuki Senior Operations Manager, Optical Design Group, Engineering Division, Optical Device Business Division.
Before each X100 lens is shipped, the MTF characteristics are measured and the lens is tuned. That is why I am confident that the photographer will enjoy the satisfaction of a lens that performs according to the original design specifications. My main responsibility was making the lens as compact as possible, and so I hope that you enjoy its easy-to-carry slim form and make it your constant companion, ready to capture high quality images that only the X100 can achieve.
Yoshitaka Takeshita Engineering Manager, Electronic Imaging Products Development Centre, Research & Development Management Headquarters.