Re: What is the correct technical name:3-mirror kaleidoscope & image made

I am not certain, but I did find a reference to ‘three mirrors each placed 
to form a hollow prism', see  http://www.words
mith.org/anu/vrml/kaleidoscope/info.html .  There is 
another site you may have already discovered,  http://www.kaleido.com/resource.htm , which provides a wide 
range of resources for kaleidoscope.

A cylinder narrower at one end than the other is referred to as a frustum 
of a right circular cone.

A solid geometric figure bounded by polygons is a polyhedron, solid 
geometric figure being comparable with a 3D image.

Again, if the two sites mentioned do not help with the terminology for the 
configuration of mirrors used, it may be better to describe it as three 
mirrors placed to form a hollow prism, along with a description of how the 
prism is position within the frustum (orientation relative to the axis, 
etc. ).

Good luck with your project, it sounds interesting.