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Measuring of the condenser NA

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  • Dushan Grujich
    G Day! Having gotten rather good results measuring the NA of microscope objectives, I decided to try and measure the NA of several condenser s and compare
    Message 1 of 3 , Feb 1 4:49 AM
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      G'Day!

      Having gotten rather good results measuring the NA of microscope
      objectives, I decided to try and measure the NA of several condenser's
      and compare them, having in mind that the system largely depends on the
      condenser quality and performance. Again, I faced a problem of finding
      and deciding which measurement method should I employ to accomplish the
      task. Obviously the simplest (read cheapest) there is, but accurate
      enough to give meaningful results.

      Searching the literature, finding several methods, I have decided to go
      on with method utilising the thick plate glass (by H.P. Gage ), found in
      "The Microscopy" by Simon Henry Gage. Method is simple enough, perhaps
      not as accurate as some other but it seems to be more than ample for
      home use. Paragraph #266 gives description on how to make the apparatus,
      then paragraph #268 gives explanation about how to use it to measure
      diameter of the light cone used in turn to calculate the condenser NA,
      explained in paragraph #268a followed with few examples.

      To make the apparatus I used one of my 60 mm (2-3/8") Optical Flats for
      which the Refractive Index is known, as is required for accurate
      determination of condenser NA. Departing from instructions in one
      detail, instead of frosting one surface I used a small thin piece of
      plastic drafting film laid on top surface for taking the measurement,
      with the assumption that it shall not influence readings too much,
      expecting that it will not introduce too large an error. Optical Flats
      are rather costly affairs to have them destroyed by frosting one of the
      surfaces. ;-)

      Otherwise I followed directions as given in the text.

      All of the testing were done dry, I left immersion tests to be done at
      another time.

      The condenser NA measurement results, rounded to two decimal places, are
      as follows:

      LOMO Aplanatic NA 1.4
      measured NA 0.93
      LOMO KOH-3 w/o supplementary lens measured NA 0.81
      LOMO KOH-3 with supplementary lens measured NA 0.36
      Carl Zeiss Jena NA 1.2
      measured NA 0.80
      Unknown maker NA 1.2
      measured NA 0.78

      I would really be appreciative of any comments.

      Cheers

      Dushan
    • Randall Buck
      Hi Dushan, I assume you had the condenser iris wide open and that the condenser was adjusted up or down relative to the stage so that the lower light bundle
      Message 2 of 3 , Feb 1 7:48 AM
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        Hi Dushan,

        I assume you had the condenser iris wide open and that the condenser was
        adjusted up or down relative to the stage so that the lower light bundle was
        minimum in size?

        Remember, to actually get NA 1.4 from a NA 1.4 condenser, you will have to
        use oil immersion on the top lens.

        Randall



        -----Original Message-----
        From: Microscope@yahoogroups.com [mailto:Microscope@yahoogroups.com]On
        Behalf Of Dushan Grujich
        Sent: Friday, February 01, 2013 4:49 AM
        To: Microscope@yahoogroups.com
        Subject: [Microscope] Measuring of the condenser NA


        G'Day!

        Having gotten rather good results measuring the NA of microscope
        objectives, I decided to try and measure the NA of several condenser's
        and compare them, having in mind that the system largely depends on the
        condenser quality and performance. Again, I faced a problem of finding
        and deciding which measurement method should I employ to accomplish the
        task. Obviously the simplest (read cheapest) there is, but accurate
        enough to give meaningful results.

        Searching the literature, finding several methods, I have decided to go
        on with method utilising the thick plate glass (by H.P. Gage ), found in
        "The Microscopy" by Simon Henry Gage. Method is simple enough, perhaps
        not as accurate as some other but it seems to be more than ample for
        home use. Paragraph #266 gives description on how to make the apparatus,
        then paragraph #268 gives explanation about how to use it to measure
        diameter of the light cone used in turn to calculate the condenser NA,
        explained in paragraph #268a followed with few examples.

        To make the apparatus I used one of my 60 mm (2-3/8") Optical Flats for
        which the Refractive Index is known, as is required for accurate
        determination of condenser NA. Departing from instructions in one
        detail, instead of frosting one surface I used a small thin piece of
        plastic drafting film laid on top surface for taking the measurement,
        with the assumption that it shall not influence readings too much,
        expecting that it will not introduce too large an error. Optical Flats
        are rather costly affairs to have them destroyed by frosting one of the
        surfaces. ;-)

        Otherwise I followed directions as given in the text.

        All of the testing were done dry, I left immersion tests to be done at
        another time.

        The condenser NA measurement results, rounded to two decimal places, are
        as follows:

        LOMO Aplanatic NA 1.4
        measured NA 0.93
        LOMO KOH-3 w/o supplementary lens measured NA 0.81
        LOMO KOH-3 with supplementary lens measured NA 0.36
        Carl Zeiss Jena NA 1.2
        measured NA 0.80
        Unknown maker NA 1.2
        measured NA 0.78

        I would really be appreciative of any comments.

        Cheers

        Dushan


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      • Dushan Grujich
        ... G Day Randall! Of course, I left iris wide open. It is stressed in the article that pinhole must be in focus of the condenser as if it is not then the
        Message 3 of 3 , Feb 1 8:11 AM
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          On 1/02/2013 4:48 PM, Randall Buck wrote:
          > /I assume you had the condenser iris wide open and that the condenser was
          > adjusted up or down relative to the stage so that the lower light bundle was
          > minimum in size?
          >
          > Remember, to actually get NA 1.4 from a NA 1.4 condenser, you will have to
          > use oil immersion on the top lens./
          G'Day Randall!

          Of course, I left iris wide open. It is stressed in the article that
          pinhole must be in focus of the condenser as if it is not then the
          diameter of the cone of light cannot be accurately measured, the empty
          space (if any) need be closed with a glass slip and bridged with oil on
          both sides. I did take time to play a little with iris, closing it down
          and seeing how it acts on the light cone narrowing its diameter on the
          frosted surface thus reducing the usable NA.

          I do understand that to achieve NA higher than 1.0 it is necessary to
          use oil to bridge all surfaces, condenser to a slide and cover slip to
          the objective lens otherwise maximum achievable NA will be 1.0 only and
          judging from my experiment even less than 1.0 can be expected even if
          allowed for errors in measurements I have taken.

          Cheers

          Dushan


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