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7189Re: [William-Optics] Re: Air-spaced versus oil-spaced lens elements?

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  • Robin Retzlaff
    Jan 23, 2006
      The lens designer I know uses a synthetic oil with a refractive index carefully matched to the glass. Protected from oxygen between the glass elements he doesn't think that deterioration over time is much of a problem. But even if after half a century an oil-spaced lens needed servicing it seems like a good compromise to me. Another myth is that they'll leak oil. Truth is that the cohesion forces of such a thin film of oil prevent this from happening even under pressure. Sealing the edges is largely unnecesary but they do it anyway. Is your f/15 a nice achromat? I'd relish a look through it.......

      Rick Jack <jack11973@...> wrote:
         How does the oil hold up to time and elements?  I know some oils used in microscope optics discolor and reduce light transmission. I've been using a 6" f15 air spaced objective for years without a hitch.

      Robin Retzlaff <robinretzlaff@...> wrote:
      Glad to help. Hopefully we'll get opinions from others and mix it up a bit.

      rfrisk <rfrisk@...> wrote:
      Great Scott, Robin - you just addressed about 99% of my questions in
      one post!! My reason for purchasing this scope is casual planetary
      observation and serious DSO observation and imaging. I have been
      strongly favoring the WO FLT-110 and appreciate the heads up for
      Tom's review. I really appreciate you taking the time to reply with
      such an informative response. It helped me out more than you know.

      Thanks again.


      --- In William-Optics@yahoogroups.com, Robin Retzlaff
      <robinretzlaff@y...> wrote:
      > We could try and start a discussion of this issue here if you
      want. FWIW I'll share with you some of my gleanings and hope for
      someone more knowledgeable to post........
      >The curvature radiuses of the mating surfaces in an oil-spaced
      design must be .....
      >The main thermal problem with air-spaced lenses are the .....
      >The amazing Flt-110, by the way has all the advantages of an oil-
      spaced design and with its......

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