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09-06-2015, 10:00 PM   #1
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Lost in translation: New Pentax D FA lenses use anomalous partial dispersion glass

I noticed that between the US and Japanese documentation, there are discrepancies as to the special glass used in the Pentax D FA 150-450mm and D FA* 70-200mm lenses.
  • The US product page states that the D FA 150-450mm lens has 3 ED elements and 1 Super ED element. However, the Pentax Japan product page says the lens has 3 ED elements and one anomalous partial dispersion element.
  • For the D FA* 70-200mm lens, the Pentax Japan product page states that there are 2 ED elements, 2 Super ED elements, and 4 anomalous partial dispersion elements. However, the US press release has an incorrect translation for the underlying Japanese for "anomalous dispersion" as "super-low dispersion". This is not the same as Super ED.
To understand the difference, I will note that dispersion is the breaking up of light into its constituent colors (wavelengths). High dispersion results in chromatic aberration, so low dispersion glass makes it easier to correct to CAs. Super ED glass is a type of glass with extremely low dispersion, more so than ED (extra low dispersion) glass. Anomalous partial dispersion glass have non-linear light dispersion profiles, where dispersion is higher or lower in a limited range of wavelengths than in the rest of the spectrum. Both types of glass can be very expensive, and play a key role in reducing chromatic aberration in today's high-performance lenses.

In other words, Ricoh is using far more exotic glass than you may have expected in the upcoming D FA* 70-200mm lens.

—DragonLord

---------- Post added 09-07-15 at 01:05 AM ----------

Even the Pentax DA 18-50mm retractable kit lens uses anomalous partial dispersion glass.



Last edited by bwDraco; 09-06-2015 at 10:26 PM.
09-06-2015, 10:19 PM   #2
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QuoteOriginally posted by DragonLord Quote
in other words, Ricoh is using far more exotic glass than you may have expected in the upcoming D FA* 70-200mm lens.
Considering that Sigma have been using their ED and FLD glass, Nikkor using high grade ED and ELD, Canon using Fluorite and ED glass in their 70-200mm f2.8 lenses. Pentax shoud do the same to keep up with the competition.
09-06-2015, 10:55 PM   #3
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I have came across with similar discrepancies too.
May be it comes from the translation Jp-En.
This lens - "1 Super ED element" or "one anomalous partial dispersion element" - is surely made of special dispersion material.
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