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 Post subject: Hemicylinder or prism in refractometer
PostPosted: Sun Feb 23, 2020 1:07 pm 
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Hi everyone,
I am new to this website. So much great information! Thank you.

My question is about the shape of the high RI glass in the refractometer. The one in the GIA Duplex refractometer is a hemicylinder. What are the optical advantages of using that shape for measuring RI?

What about the Dialdex that Gem-A provides to its students? I believe it is a truncated prism. Again, why is it shaped like that?


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 Post subject: Re: Hemicylinder or prism in refractometer
PostPosted: Sun Feb 23, 2020 1:19 pm 
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Joined: Sun Oct 16, 2005 12:22 pm
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Location: San Francisco
Hi Valaya and welcome.
All refractometers use hemicylindars. See:
https://www.gemologyproject.com/wiki/in ... fractomete


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 Post subject: Re: Hemicylinder or prism in refractometer
PostPosted: Sun Feb 23, 2020 2:16 pm 
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Hi Barbra,
Thank you. I have read the chapter on the refractometer in Gemology Project. Really helpful but here are the two concepts I don't grasp:

"In a hemicylinder, the incident and exiting ray always reach the boundary at a 90 degree angle when directed to the center. Refraction doesn't occur when a light ray is at 90 degrees to the boundary. A hemicylinder is used so there will be no refraction of the light entering nor leaving the denser material. "
Is that the goal of having a hemicylinder, i.e. the fact that all incident and exiting rays will pass through the hemicylinder without being reflected nor refracted? How does that work from the point of view of optics?

Thank you!


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