parametrised microscope darkfield masks

Darkfield masks are used in microscopy to block direct light from the light
source, but allow indirect light to pass through cutouts in the filter,
which scatters and illuminates the specimen indirectly, thereby increasing
contrast with translucent specimen.

This design is provided with OpenSCAD source, which has been written to
parametrise relevant values for customisation. Interface variables are:
filters : the count of filter sets (one set consists of all different filters of one size)
height : material thickness. Also determines rim and spokes strengths
outer : outer filter diameter (fits Swift SW380T)
smallesthub: smallest size of light blocking pad
smallestcutout: smallest distance between hub and rim (extent of cutout)
spokes : number of spokes
spacing : distance between filters

I suggest to print the device in ABS, because with a few strokes over
sandpaper a nicely smooth surface can be obtained.