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I have owned several Zeiss telescopes over the years as an amateur astronomer and enjoyed each and every one of them. There is something about a Zeiss that appeals to me. It may be the craftsmanship - they are built like tanks. It's certainly the lens quality - the figure and polish is second to none. But then again there's the history - so long a run in amateur telescope market only to be haulted in the mid 1990's. It's enough to keep me coming back to them again and again. So, recently when I was offered the opportunity to purchase a Zeiss ED80/840 lens in new condition, I took another plunge.
The Zeiss ED80/840 lens is a real odd ball. It's certainly an enigma in the Zeiss amateur line, shielded in a some mistery. From all I can gather, they were made in 1994/1995. The idea was to make a scope that would be be a step above the achromat line of AS (Sonnefeld designed) scopes and yet be more affordable than the top-of-the-line APQ fluorite apos. There was already an AS80/840 refractor and to begin with, a number of these lenses were put into AS cells & OTA's with the only change being the designation ED80/840 on the dewshield. I have seen only three of these models. However, before the ED80 could go into mass production Zeiss made the decision to get out of the amateur telescope market. According to Baader Planetarium in Germany ( A Zeiss dealer and only authorized repair facility), only 30 of these lens were made by Zeiss, making them a very rare lens indeed!
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I started by setting up a test bench. The Zeiss lens at one end and a diagonal at the other. This enabled me to determine the position of the focuser so that its back focus would accomodate all my various eyepieces as well as my digital camera, and to determine the tube length. Once these measurements were made, I began work on the OTA.
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First, I machined a tube plug with an 1.25" hole in it to fit my laser collimator. With the laser in place (shim-fit), I positioned the plug so that the laser beam hit the center of a paper disc inserted into the other end of the tube. While aligned I layed out the mounting bolts for the plug and drilled and tapped them. This plug will be the basis for properly aligning the tail-piece and focuser.
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At this point I drilled and tapped the plug for mounting the tail-piece and opened the hole in the plug to allow clearence for the focuser's drawtube.
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The tail-piece that I machined, serves as the transition between the OTA and focuser. Holes were drilled in it for mounting it to the plug and then more holes were drilled and tapped for mounting the focuser to it. When ready, I mounted the tail-piece to the plug.
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and then the focuser to the tail-piece, checking the alignment again with the laser.
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Next I began work on the other end of the OTA. I machined and threaded a nose-piece and fitted it to the OTA.
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