Originally posted by normhead And as has been pointed out countless times, lenses like the 31 and 77 are loved more for their handling of out of focus areas than they are for their sharpness. My Sigma 18-250 could never match my DA*60-250 for bokeh, even shot at the same FL and aperture. That's why we still have the 60-250 and gave the 18-250 to my daughter in law. Digitalis once posted a comparison of the 31 and Sigma 30 1.4. There was a very subtle difference in OoF areas in favour of the 31. That's why the 31 is highly regarded and the 30 1.4, not so much. What many seem to fail to understand is that the differences between average lenses and really good lenses, can be very subtle. If you're looking for a huge difference with lenses made in the last 10-15 years, you probably won't find them. And I guarantee you, if Pentax could do what they did with the 31 and 77 with every lens, they would have. There seems to be an element of luck involved. You're much better off to buy what's really good, than hope something better will come out. The odds are seriously against that, although, it could happen.
Or buy what has the aperture and FL you need and don't worry about pixie dust. There's more than one way to think about lenses.
Exactly!
Yet pixie dust is really a matter of engineering and physics. The shapes of the bokeh, color casts, color fringing around bokeh, "busy" bokeh etc. are all predictable consequences of the lens design, manufacturing techniques, and materials. It's simply a matter of the designer looking into it (and having a company that's willing to pay the development and manufacturing costs to build in pixie dust).
Whether a lens designer spends time optimizing the design for pixie dust or devotes it to corner-to-corner DXO MTF resolution is the bigger issue. (And whether the market rewards companies who try to win the DXO game versus the pixie dust game is an even bigger issue). It seems that Pentax already has competitive options for pixie dust lenses and is now trying to fill-in it's offerings on the big-aperture, DXO/MTF side of the spectrum.
And maybe they are being extremely clever about it. One could describe their intended lens line up as:
31Pixie, 35DXO, 43Pixie, 50DXO, 77Pixie, 85DXO