Originally Posted by CMur12
My understanding is that the 7-element 50mm lens that succeeded the 8-element version was made with special (radioactive; thorium?) glass, which Pentax probably felt offered the same performance with one less element. I'm pretty sure the radioactive glass cost more than the more common glass. I don't see it as Pentax lowering their standards.
I'm far from an expert on this (hopefully others will offer their take...) but my reading is that the cost associated with the 8 element wasn't just that it had one more piece of glass, but rather than it had a cememted triplet that was very expensive to manufacture. Every bit of info I've come across agrees that the 7 element was more affordable to produce*.
I don't know the relative cost of thorium vs regular glass, but given that Pentax also used thorium in their cheaper 'kit lens' 55/f1.8, I can't imagine the difference is significant.
*Having said all that, none of the comparisons I've seen between the Super-Tak 7 and 8 elements suggest a notable difference in image quality.