I just ordered a Rodenstock APO sironar S 210 mm to go between the 150 mm sironar and the 360 Nikkor T. [Buyer's remorse: should I have gone with a 240 instead? Please don't tell me ;-)]. Anyway, looked at the Rodenstock tech data, and the chromatic correction chart shows the curve passing zero twice, around 438 nm (blue) and around 540 nm (green). I thought the term "apochromatic" means corrected for THREE wavelengths, while corrected for two wavelengths is "achromatic". Am I missing something? Is this some sort of terminology inflation in LF-gear? My microscopy lenses (Zeiss planapos) are truly apochromatic.
The lens seems to be quite fine according to the messages and reviews I've seen, so I'm not worried about performance. Just wonder about some terminology.
Thanks in advance for the collective wisdom.
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