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Does an APO always have three lenses?

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#26 ridurall

ridurall

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Posted 14 November 2003 - 09:33 PM

Here is what my Takahashi manual says on the subject of Fluorite & Apochromatic refractors.

"When Takahashi first designed the fluorite apochromatic refractor, they realized that the optimum design placed the fluorite element in front. Coating technology of the time did not permit this to be done. Therefore, an alternate but excellent design placed the element in the rear. Now, due to a production and technological breakthrough, fluorite can be hard multi-coated. The new FS Series benefits from this by placing the fluorite element in front with a low dispersion glass in the rear. The result is the finest apochromat on the market today. This breakthrough not only improved on an already outstanding design, but it dramatically lowered the cost."

Now before you flame me. I just copied this from my manual. I do like my little FS-78 and can't say I have any problems with color if I'm using a quality eyepiece.

Ron D

#27 Ron B[ee]

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Posted 14 November 2003 - 09:46 PM

Here is what my Takahashi manual says on the subject of Fluorite & Apochromatic refractors.


Excellent point, Ron D. While we're on this thought, here's an interesting writeup about Takahashi flourite lens.
http://www.lsstnr.com/FluoriteAdv.htm
However, the last paragraph does need revision as the TOA series now uses "flourite" glass (not crystal).

Ron B[ee]


#28 ridurall

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Posted 14 November 2003 - 10:17 PM

I had not read that Ron B. Thank you it was interesting.

Ron D.


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