Hello science students! This is the third installment of our telescope optic study. Check back to the Smith’s Kotoen Astronomy Course Home Page now before proceding, and also have a look back at previous soapbox postings, especially the post dated Aug 28, 2011.
It was only days ago that astronomy suddenly became cool again with the Annular Solar Eclipse passing right over our heads on the Pacific side of Japan. Next on June 6, all day Wednesday, solar revelers have the opportunity to witness a Solar Venus Transit, an event much rarer than the eclipse.
So astronomy is no longer a nerd’s passion but absolutely back in the ultra-cool circle where it always should have been….. because it’s cool.
On the other hand the technicalities of optical quality, and of optical glass quality in particular, can hardly be called cool in the same sentence as astronomy. At least most people wouldn’t. But then a couple of the really smart students at my school in Kotoen are not like most people. For them I offer a basic glossary of optical glass evaluation parameters which is homework for the next lesson. The vocabulary goes as follows:
glass tone – astigmatism – spherical aberration – chromatic aberration – contrast – center sharpness – edge of field sharpness – light transmission – field curvature – focal shift – pin cushion distortion – field of view – apparent field of view – coma aberration – parfocal – orthoscopic – aplanatic – apochromatic – Abbe number reflective properties – Abbe number refractive properties – thermal expansion coefficient – Abbe number dispersion properties
Glass Types Under Evaluation – Corning Pyrex, Schott Zerodur, LZOS OK-4, Ohara FPL-53. The Takahashi Mewlon pictured above uses Corning Pyrex. All Carl Zeiss products including the binoviewer you see on the Mewlon use Schott glass. The Pentax eyepieces use Hoya optical glass.
For a look at my most recent lens evaluation:
Kokusai Kohki www.kkohki.com Telescope Store in Kyoto
Martin Werner Zander, Smith’s Partner
Owner, Smith’s School of English in Kotoen