Here is a Bigma photo taken, admittedly with Canon gear as I do not have this lens on a Pentax mount.
I like the Bigma for its versatility. When your stalking things in nature, you just never know what you will come across and having a 50mm to 500mm focal length range on tap, has gotten me that photo that I could not have gotten with a smaller focal length range. When dealing with nature, you just never know what you will find and where.
Anyways, here is a photo taken maxed out at 500mm. Any blurriness in the shot was due to my hand holding it at the time. The lens is fantastic considering this is a shot I could not have gotten without having that extra 100mm range.