I sold my TMB152's on Astromart to fund the TMB175 project. The lens was aquired directly from Thomas Back. The tube design was inspired by the large "CNC" models of TMB scopes, where a threaded-rod frame runs through a phenolic tube and pulls the focuser receiver and lens counter-cell into the tube under tension. The OTA tube is a fiberglassed phenolic tube purchased from publicmissiles.com (rocketry hobby supplies,) it was very nicely made. Like the TMB152 project, the focuser receiver was machined to receive either 2.7" or 4" Astro-Physics focusers. The dewshield assembly was a "rare score" on Astromart of an actual TMB175 dewshield assembly that Tim Povlick had lying around! The 3 major aluminum parts were turned from billets by Jim Eggers of Aeroquest machining outside of Palmer, Alaska. My planetary views from this scope, are, as of yet, unsurpassed. I think the TEC200 is going to take the prize shortly though. (Later Note: Yep! Aperture Wins Again)