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    Re: USN MkII Sextant Telescope lens coatings and cleaning?
    From: Todd Spath
    Date: 2023 May 23, 17:36 -0700


    Thank you for your feedback. There are 7 achromats in the MkII telescope. Its possible that some have bond line issues, but that doesn't seem to be the predominant case. As I tilt individual doublets, in most cases I can see two distinct patterns which can be shifted relative to each other indicating that they are not on the same plane. I could be seeing one surface and the bond line, but not likely the bond line alone. I think I'm seeing the exterior surfaces. Also, when tilted to a glancing angle relative to a light source, I can still detect the pattern on the near side and the other side (or interior?) texture goes away. I'll have to try some surface wetting test with immersion oil or similar. I would expect a surface issue to be modified (cleared or blurred) while the bondline appearance won't be altered.

    I'm glad your Plath repair went well. How did you realign the singlets when bonding? Just mechanical vee block or similar, or did you have optical means?

    Thanks again,


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