Originally posted by Digitalis There is an extra Aspherical in the Pentax lens, and no mention of the XR lens elements by another name. Which suggests that there have been some alterations made to the Tamron design.
Maybe. But I think the more likely explanation is that Pentax has merely chosen to highlight different aspects of the lens, underscoring the use of aspherical and low-dispersion glass, while ignoring the XR elements. Furthermore, I don't find that the Pentax lens features an aspherical element that is entirely lacking in the Tamron lens. Look more closely at the optical formula of the Tamron:
From this drawing we can see that the Tamron uses three "Glass Molded Aspherhical" lenses and one "Hybrid Aspherical Lens". That's four aspherical elements right there. And from the
Ricoh-Imaging website there's the following:
Quote: Consisting of 17 elements in 12 groups, 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.
I would suggest that would what Tamron calls "hybrid aspherical lens" corresponds to what Ricoh calls "anomalous-dispersion-glass aspherical optical element." Moreover, in Tamron's own
explanation of hybrid aspherical technology, they write about "AD-Hybrid Aspherical " elements (where AD stands for "anomalous dispersion").
That doesn't mean, of course, that Pentax might not be using their own glass elements. But given the $1,299 pricetag, I think that's rather unlikely.