This is a very good lens for shooting butterflies "in the wild".
For example, this photo has not been cropped, and I am not even at the minimum focus distance.
Had I been at the minimum focus distance, this Eastern Tiger Swallowtail's wings would be touching the edges of the frame.
The lens itself is not particularly heavy, is very well built, and has a well-dampened focus throw that makes slight adjustments to focus very easy.
It is also happily compatible with the Pentax Rear Converter A 1.4x-L, which is actually sharper than the HD DA 1.4x TC, according to Pentax Forum's review.