Vertical and Horizontal Stripes
This week I was off the nano-lathe and focused instead on creating images to match the cut planes of the mirror facets. I put both of these into my optical system for testing and figured out that there would be lots of incremental changes to make. I began by printing a series of small scale translucent images to allow the light travel through the image and onto the mirror plane.
I created both vertically and horizontally striped images to reflect at 90 degrees to the cut mirror plane. That is, for the mirror with vertical cuts, I reflected/projected a horizontal stripe image and vice versa. This allows me to see how much the depth of cut bends the light and if my next program for the nano-lathe requires deeper cuts. These striped images are just for optical testing, when I work out how much the light bends I will create a series of images and matching mirrors.
Within the images I added a fine black stroke line in between each coloured stripe. This allows my eye to pick up the change in direction of the light (stripe) more easily – a trick I picked up from the 19th century artist-engineer Charles-Émile Reynaud! He used a black background in his image frames so that the viewer could more easily perceive the change in the characters in the foreground.
Image and mirror holders
After preparing the images, I modelled up and 3D-printed some image holders so I could control their position in the optical system. Originally I thought that the image size needed to be exactly the same as the mirror, but when I tested this, it turned out that the image frame needs to be significantly larger than the mirror to compensate for the distance between the image-object and the surface of the mirror.
Before placing the facets onto the polygon gig, I needed to test a single mirror facet in my optical system and therefore modelled up a small holder for the mirror.
At the same time Tom Cave from the School of Physics Workshop make a brass gig allowing me to easily attach the aluminium facets onto a holder for cutting. This will make centring the placement of the facet on the spindle much easier – for when I’m back cutting again next week on the lathe!
Geoff and I have been working on a python script that we will use next week once back on the machine. We’ve been working towards achieving more stepped and deeper cuts on the aluminium facets, to see if this changes the reflected image more dramatically.
To begin a conversation with Geoff about the mirror cuts, I 3D modelled and printed some surface profiles. Understanding now how the nano-lathe works has modified my thinking about how to make the mirrored facets. Geoff wrote a python script to approximate the spline into a series of points and then turned this into g-code for the nano-lathe. The machine also cuts very slowly, for example a facet of 18mm x 25mm takes about 4 hours to cut about 120 microns (0.12mm).
After several years of working with miniature architectural structures in glass and the moving image, projected image-light had firmly cast its spell on me. I projected video-animations or dreamscapes to wrap around my constructed glass buildings. The glass walls, which once encapsulated spaces full of life, now abandoned and empty, released fleeting memories in the form of nonsensical fragments of image-light. As an object maker, I carefully controlled the translucency of the glass, allowing the image-light to enter into the walls and remain there. I focused on glass as a material substrate with which to hold these fleeting images, rather than as part of the mechanism that generated them.
I spent many days in my studio deconstructing various old projection devices, extracting their lenses and light sources. Each time I held up one of the lenses in front of my studio window, the scene from outside was somehow magically transported onto the wall behind me. It seemed unfathomable to me that the material of glass, just by being formed and polished in a particular way and interacting with natural light, could transport an image across my studio, creating its own parallel space-time. Determined to understand the uncanniness of this deceptively simple technology, I looked to the history of lens making and its application.
I was amazed by the 17th century natural philosopher and lens maker Christiaan Huygens’ combined mathematical knowledge and material skill in forming telescopic lenses and Rene Descartes’ determined, but ultimately failed quest to build an automated machine to grind and polish a perfect hyperbolic lens. But when I encountered the early optical technologies of preternatural philosopher and natural magician Giovanni Battista Della Porta, (some 80 years before Huygens), a whole new world opened up. The experience of wonder witnessing the uncanny ability of glass to transfer and image of an object across space and time was explicitly used by Della Porta.
During the development of one of my image systems Ghost in the Machine, I came across the 19th century artist-engineer Charles-Émile Reynaud. Reynaud developed a system of optical mechanics first with his praxinoscope and later in his more elaborate Théâtre Optique. When I witnessed these devices in motion at the Cinémathèque Française, animated characters reflected themselves off mirrored polygons, which rotated around static sources of light. Brought to life through the movement of a mirrored polygon, these images appeared like spectres, suddenly re-activated from the dormant past of the nineteenth century.
The praxinoscope uses an optical mechanism of a mirrored polygon sitting inside an encircling metal drum twice its diameter. Reynaud described the polygon as a ‘cage of mirrors’, a series of twelve small vertical mirrors glued to each other and positioned in the centre of the drum. The polygon and the drum rotate on the same axis. Each mirrored facet of the polygon reflects a single and different image frame painted on the inside of the drum. Collectively, the images make up a frame-by-frame sequence of movement, so that when the device rotates in front of a viewer, it creates the appearance of a moving image. Reynaud later developed the praxinoscope device into a more elaborate form of the Théâtre Optique, which used hand-painted translucent glass slides on a rotating device allowing up to 250 image frames. He rear-projected these reflected images through an objective lens system onto a screen.
While developing Ghost in the Machine it proved challenging to generate a projected moving image that wasn’t blurred. To overcome this problem I applied Reynaud’s technique of individually reflecting each image frame on to a matching mirrored plane. This concept worked because in contrast to my image frames, where each image presents a different stage of movement, each segment of mirror is identical. It is the image reflected from the mirror (and not the translucent image frame per se) that travels through the objective lens and is projected on to the screen. So while the mirrored plane renders the moving image legible, its reflective properties hide the mirror in plain sight – as the viewer of the projected image, I don’t perceive the changing mirror plane, only the different stages of movement foregrounded on an apparently static background.
Fabricating the polygon proved to be the most problematic component of Ghost in the Machine, but also one that provided numerous ‘next steps’ in my practice. Machinist engineer Neil Devlin at the RSP who, being the innovative master he is, milled and polished the polygon by fly-cutting the surfaces using a diamond tool from the School’s ultra-precision lathe. The rotating polygon, the process of making it and understanding optical mechanics gave me new ideas for creating moving images in novel ways.