Returning to pixelated patterns and 3D image-objects

Pixel patterned facets. Here the pixel size is increased from 1 to 1.5mm and the pattern difference from one facet to the next is more controlled than previous tests

Following on from previous tests with pixelated patterns I wanted to find out if modifying the ‘pixel’ size on the surface of the mirror would create a more distinct projected image. I increased my ‘pixel’ pattern size using Photoshop and then imported these files into Jupyter so that Geoff could help me edit the Python script to generate the g-code for the nano-lathe. Each colour in the pattern represents a specific depth of cut in microns. For example the blue pixels have the deepest profile cut at 120 microns and the green pixels are cut to 60 microns.

‘Pixel’ images created in Photoshop. Each colour represents a different depth of cut, for example the blue ‘pixels’ have the deepest profile at 120 microns and green ‘pixels’ are cut to 60 microns.
Colour map generated by Geoff’s Python script from one of the Photoshop images above. This is then translated into a NC format file containing the g-code for the lathe.

Resolving problems of distance from image-object to mirror plane

Projecting the image from the pixelated mirror frame. The image is being projected at a 45 degree angle and therefore only the right half of the mirror frame is effecting the image.

Above is the projected image created by using one of the ‘pixel’ mirror facets. To front-project the image, I placed the mirror at 45 degrees to the image-object (translucent slide), resulting in only half of  the mirror surface effecting the projected image. To achieve the optimal reflection of the image-object in the mirror (which is then projected through the objective lens system onto the wall), the mirror needs to be very close to the image-object. Two considerations emerged relating to this required proximity between the image-object and mirror. The first was that to overcome the 45 degree angle issue, I tried using a second mirror to reflect the light in a forward direction. However this doubled the optical distance from the image-object to the mirror facet. The second consideration was that because the mirror facets are part of a rotating polygon, a certain amount of space (a little more than the radius of the polygon) is required for the polygon to rotate without touching the image-object.  This means the image-object is too far from the mirror plane. After conversations with Geoff about resolving this issue,  we decided to image this image-object just before the surface of the mirror using a wide aperture short focal lens. To make such a lens we needed a large diameter (75mm) relative to its focal length.

50mm acrylic lens blank made by Neil Devlin
50 mm acrylic blank in the aluminium, both fabricated by Neil Devlin. The jig is vacuumed onto the nano-lathe spindle during cutting.

Neil Devlin fabricated the optical acrylic blank and aluminium jig for us to use in the nano-lathe. To make the shortest focal length possible we will cut a lens using the full 50mm thickness of the blank. Stay tuned for the result!

Testing 3D image-objects
During the last few weeks I also tested how, using an object instead of a 2D image (translucent slide), effects the projected image. Working from previous image-object works, where I created translucent printed objects to generate projected images in ‘3D’, I was interested if this would have the same effect when using the mirror facets.

This image, depicting an empty space stairwell is pure light. It is generated though a translucent 3D printed object placed in one of my optical image systems.

Simulating the 2D lined image that I had previously created in Photoshop,  I modelled the 3D image-object using 1.5mm lines of different depths. I wanted to know if the different depth of each line would affect the transfer of light and hence the projected image. This 3D image-object was printed using an SLA Form printer with translucent resin. I discovered that this line object requires optical polishing for it to transmit sufficient light!

Top view of resin printed translucent 3D image-object.
Profile view of different depths of the lines for the image-object.
Projected image generated through printed ‘line’ object.



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