Inkjet printing technology that “functions” in a digital camera

For more than 20 years since the launch of the RICOH GR series in 1996, in the era of film cameras, we have continued to develop these high-end digital cameras as snapshooter cameras based on the same concepts (high image quality, quick photographing, portability and evolving. For the distinctive specification models, the RICOH GR Ⅲ HDF and RICOH GR Ⅲx HDF, we applied our own inkjet (IJ) printing technology to develop a soft filter (a filter that bleeds light and softens the mood of a photograph), to expand the depictive representation possible without sacrificing the quick photographing, which is a key point for the GR cameras.

The Highlight Diffusion Filter (HDF) soft filter we developed enables a softer expression that emphasizes the light. This realizes nostalgic photography like that in film photography and movies. The features of these images are that the highlight areas are diffused and the areas around the highlights are blurred (Figure 1). Based on the concept of GR, we wanted to make it possible to capture various scenes in everyday life, so rather than adding a flamboyant and striking effect, we instead made adjustments to produce a filter effect that users will be able to utilize for a long time to come.

To make it possible to turn the filter effect on and off at the touch of a button, it is necessary to place a thin, small and lightweight filter inside the optical path in the photographic lens system in the camera. The requirement to be thin is to prevent an adverse effect on the image formation performance when the filter is inserted or removed from the optical path. The requirements to be small and lightweight are to realize the driving of the filter inside the camera.

We successfully developed the HDF by combining the optical technology and IJ printing technology of Ricoh to develop IJ manufacturing technology for a thin optical filter.

To reduce the thickness of the filter, we developed the technology to place structures that perform the desired optical functions on the surface of a filter, rather than inside the filter. IJ printing technology made a great contribution to this development, as it enables detailed and highly precise drawing on a wide variety of media. IJ printing also does not require an original plate for the printing, so it has the benefit that the filter effect can be fine-tuned through the production of a large number of prototypes, even when the research and development period is short. By reducing the thickness of the filter, we were able to minimize the change in the imaging performance of the photographic lens system when the filter is inserted or removed.

To reduce the size and weight of the filter, we adopted a layout that places the filter near the aperture stop of the lens system (Figure 4). With an aperture stop, the light path in the photographic lens passes through nearly the same position regardless of the angle of view. The advantage of this layout is therefore that even with a small filter, the filter effect can be applied uniformly across the entire screen. This layout requires the insertion and removal of the filter inside the photographic lens system, so it was necessary to devise a method to make the filter thinner. Making the filter smaller and lighter also made it possible to reduce the size of the drive motor, so we made it possible to turn the filter on and off without increasing the size of the camera.

In order to achieve a desired optical function on the surface of a filter, it is necessary to precisely control the density characteristics, size, shape, and arrangement of the structures to be placed on the filter surface. We achieved this by applying the IJ printing technology Ricoh has developed so far.

Picoliter^* sized ink droplets are arranged on the filter surface. While optimizing the number and placement of those ink droplets, we also realized a positive effect on the filter characteristics by using multiple types of ink droplets with slightly varying sizes. This is realized with our unique IJ printhead that can eject tiny ink droplets (Figure 6), and with our multi-drop control technology to control the size of the ink droplets (Figure 7). In addition, we used ultraviolet-curable (UV) ink to ensure that the ink droplets maintain a dome-like shape on the surface of the filter while also maintaining an appropriate density of ink droplets for the filter expression. Moreover, we formulated the ink to withstand constant mechanical operations when the filter is switched on and off in harsh environments—as in high and low temperatures or humidity in which ink may peel or discolor—or repeatedly inserted and removed, which may also lead to deterioration.

It is also important to ensure stable mass production of these technologies in which the filters are made as thin as possible to realize weight reduction and desired optical properties. Because extremely thin films quickly become distorted and wrinkled and are also difficult to set in the printing equipment and mount on the camera after printing, production equipment must also be able to stably place ink droplets in the desired position. In the mass production process, all films must achieve the same quality, so the production technologies, which we have used so far to produce many precision instruments, played a major role.

By combining the optical technology and printing technology that Ricoh has developed over many years since the foundation of the company, we worked on new ideas and challenges in the form of printing technology that functions inside a digital camera.

We will take advantage of this initiative to further explore the possibilities and development of new filters that can contribute to the culture and history of cameras and photography.