Originally posted by Adam Is the difference really that big? If it is, I'll go ahead and add it!
Bojidar Dimitrov has separate entries:
Pentax Zoom Lenses with Short Focal Lengths
Summary: Optical formula is different: old 12 elements in 11 groups, new 11 elements in 10 groups. The new one is 5g lighter. Pentax also claims that front and rear element coating is different. Finally, first tests indicate improved corner sharpness at 18mm and 55mm as well as improved close up sharpness at 55mm.
Definitely different and hence it should have a separate entry.
Also: DA 55-300 is almost there (already listed at Amazon and Henry's) so you can add that one too in one shot.