I could be wrong, but I think it's plastic AL some sort (same as FA*24 AL). Pentax Japan web site doesn't seem to emphasis it's glass AL, like the FA31.
The FA* 24 mm. 2.0 has a "sandwich" aspherical element (aspheric plastic surface on a glass lens), but the FA 35 2.0 has a molded all glass aspherical element.
Carlos
Could the 24mm plastic surface be the cause of its rather high CA?
Andre
