Originally posted by Kunzite Can we trust press releases to be accurate? If they are, that would be interesting...
From DPReview:
"To achieve this feat, Tamron has employed an exotic optical formula that makes extensive use of special elements. It includes three Low Dispersion (LD) glass elements, two Extra Refractive Index (XR) glass elements, three glass molded aspheric elements, and one hybrid aspherical element in its 17 element / 12 group design."
We have the 4 asphericals, what doesn't match is the LD+XR vs. ED.
The wording of the press release is perhaps slightly inaccurate, or Ricoh's website and optical design chart are inaccurate. (I'd guess it's the press release.) Either way, the Pentax version of the lens does indeed appear to have different elements than the Tamron-badged version. From Ricoh's product description on their website: "the newly designed optics feature three ED (Extra-low Dispersion) optical elements, one anomalous-dispersion-glass aspherical optical element and three aspherical optical elements to accommodate super-high-resolution image sensors."
Not sure if the hybrid aspherical element is the same as the Tamron one (since they don't explicitly say "three
glass ashperical optical elements,") but from the optical design shown in the chart, the front glass aspherical element in the Tamron has been upgraded to anomalous dispersion glass. (Though I'd imagine it does mean the other three are glass since they did go out of their way to specify the material of one aspherical element--it wouldn't make sense to bundle the other three together if they're not all the same.)
Also, I like that they threw the phrase "super-high-resolution image sensors" in there.