ZP_Salon

Making a zone plate: A pinhole plate is a plate with only one small hole but a zone plate has by far complicated pattern in the plate. Moreover, size of the pattern is very small in the case of a zone plate used for taking photographs and usually there are more than ten concentric slits within a small area with a diameter of several millimeters. Therefore, it is difficult to make a zone plate by drilling a metal plate as the case of a pinhole plate. As applications in scientific and engineering fields zone plates are used for non-visual light beams, especially, for short wavelength waves such as ultraviolet lights, X-ray, gamma ray and so on, and , therefore, the patterns of zone plates are finer for these applications. Usually these zone plates are processed by high precision technology and it is difficult for a non-expert to shape a zone plate with an extremely small pattern. To cope with this difficulty usually a very simple method to use a photographic film for a zone plate is employed.

The simple method to make a zone plate is as follows: (1) calculate zone sizes of the necessary zone plate, (2) draw a large pattern of the zone plate such as several 10 to several 100 times larger than the pattern of the necessary zone plate, (3) take a negative monochromatic photograph of the above magnified pattern by a film camera so that the size of the zone plate image on the film is the same as that of the necessary zone plate, and (4) use this film as a zone plate. Because we use the film directly as a zone plate to take a photograph, it is very important that the size of the pattern on the film is the same as the originally designed pattern. For this sake the distance between the magnified pattern and the camera should be carefully adjusted by considering multiplication of the magnified print and the focal length of the taking lens of the film camera. Though the above whole process can be carried out by ourselves, there are convenient web sites or softwares available by which the steps (1) and (2) are carried out automatically. A free software for Windows, Zone Plate Creator and a web site, Zone Plate Generator are useful examples for this purpose .

Zone plate camera: To take a zone plate photograph one must, naturally, prepare a zone plate camera. As I use a digital SLR, I fit an “interchangeable zone plate” of my own to the digital SLR instead of a usual interchangeable glass lens. This is same as my way to take a pinhole photograph. Needless to say one can use a self-produced camera body as the case of a self-produced pinhole camera. However, it should be noticed that a distance between a zone plate and an image screen should be carefully adjusted because the focal length of a zone plate is given definitely. Moreover, preparing a zone plate itself is a more complicated and more time-consuming task than preparing a pinhole plate. As it is possible to buy a ready-made zone plate by mail-order, it may be a good idea to buy such a zone plate for the moment and to try to take a zone plate photograph.