A sample presentation apparatus comprises a round support movable in an optical assembly and having a flange region and an elevated gear shaped region having indexing gear cogs at intermediate radius locations of the support; a sample carrier slide holder removably supported on and movable with the support, the slide holder having at least one arm extending radially from a central hub of the sample carrier slide holder and being aligned between a first pair of indexing gear cogs; and at least one sample carrier slide removably supported on the support and aligned by the first pair of indexing gear cogs. In another embodiment of the invention, a self-aligning movable platform and support apparatus in an optical assembly comprises coarse and fine alignment mechanisms.