Originally posted by Adam The optical design of the 100mm dates back to the 80s hehe. The DFA and FA versions actually share the same optics.
But why the FA is much sharper and bigger? Not only sharper, it has less aberations and fringe.
Originally posted by lesmore49 Are you relatively new to Pentax ?
A couple of years, why?
Originally posted by JinDesu Closest of your choices, with the same groups and elements, but different filter diameter and generally a different shape.
Would be highly unlikely, considering it's rear focus motor, different number of groups of elements, and I don't think lens construction works that way.
The Sigma 2.8-4.0 came out after the Pentax 17-70. Also different number of groups of elements. Not the older one either, because that one had 15 elements, while the DA 17-70 has 17 elements.
Definitely not the Tokina, which has 9 blade aperture vs the 8 in the DFA
The easiest thing to do is to compare lens construction diagrams. I think most of the Pentax lenses have lens diagrams available for viewing.
About 18-135 - If we look at the lens it is 18mm with streching to 135mm, my theory is that removing some elements from the long end made the lens 135mm instead of 250mm and that's why the 18-135 is so poor performer after 50mm. Sigma 18-250 also look like possible donor, it even zooms the right way(like the pentax).
My point for this thread was - does pentax develops lenses now days or they use other companies for the job and just re badge them.
Last edited by simbon4o; 01-05-2013 at 01:51 AM.