Luminar, but not Zeiss!
The Zeiss Luminar series of photomacrographic lenses is famous among practicers of this field of photography, because these lenses provide a very high image quality (on this site, see here, here, here, here, here, here and here). Whenever one mentions the Luminar name in the context of camera lenses, it is implicitly meant that one means Zeiss Luminars. However, here is one Luminar lens not made by Zeiss, but by an unnamed Japanese maker:
This is a cheap 75 mm f/3.5 enlarger lens in M39 mount. Neither the lens nor the box display any information about the maker, except for a generic "Lens made in Japan" engraving. No instruction sheet is available.
The lens barrel and plastic front lens cap are identical to those of 75 mm f/3.5 enlarger lenses made by Omega and branded in various ways (e.g., Voss, Vivitar). Lenses marked Vivitar are slightly different from the one above in that the front portion of the barrel is not anodized (at least in the specimens I have seen). Voss lenses were distributed with cheap Bogen enlargers, and the general opinion of these lenses is that they should be replaced as soon as possible with something better. Therefore, the interest of this lens lies only in its use of the Luminar name and as a collector's item.
The optical design appears to be a three-element design derived from the Cooke triplet (which, by coincidence, is the same used in most Zeiss Luminar lens models!), with the typical arrangement of convex front and rear elements and concave intermediate one, albeit the rear element is biconvex, rather than plano-convex like in the original Cooke triplet. The two front elements are mounted in a barrel subassembly, and could not be separated for further examination. The five-blade diaphragm is mounted between the intermediate and rear elements.
Other enlarger lenses made by Omega include the Omicron-EL series, which, despite rumours to the contrary, was not manufactured by Nikon for Omega. Incidentally, the ugly but predictable Omegaron name was not available for Omega enlarger lenses, because already used by Rodenstock for a series of enlarger lenses. There are also old Super Omegaron medium-format camera lenses with built-in shutter made by Koni Omega.