While the length of this lens piece is specific to the lenses used here, due to the modular nature of the DOME it would be trivial to adjust this dimension to suit alternative optics. Positioning both the camera and projector perpendicular to the sample stage results in significant lens flare through which imaging is difficult. To circumnavigate this the projector is angled at 10°, positioning the bright spot created by the light source of the projector out of the camera field of view (FOV). The exact spacing between critical optical components is given in Figure 5.
Characterisation of imaging and projection modules
The modular design of the DOME allows for interchangeable levels of magnification using a tube lens and an RMS threaded tube to mount different microscope objectives. A low magnification of 9X is suitable for larger microsystems of the order of hundreds of microns in size such as multi-cellular algae, while a higher magnification of 90X is appropriate for smaller agents such as mammalian cells or bacteria.
To assess the imaging and projection capabilities, we began by comparing the 9X and 90X magnification settings and used Volvox as an example subject. Volvox are an algae 350–500 µm in diameter where a single spherical colony houses up to 50,000 cells. At 9X magnification, many colonies can be seen in low detail whereas at 90X magnification only a few at are visible but smaller features such as daughter colonies within the body of each Volvox are clearly seen (Figure 1e). A scale for both magnifications was calculated by imaging a measuring ruler.