Uncommon Vivitar 600mm Pre-Set T-mount Telephoto Lens. #37900707. Lens splits in two for ease of storage. With front and rear "rifle sights" and focus assist lever. (Signs of normal use, slightly musty from storage, some internal fungus/coating marks to front element). Last image taken with this lens at f8 on Micro 4/3rds DSLR with M42 adapter.