I am looking for an Ultra wide zoom on my GX-10. I have found some review of two lens that seam okay: Pentax DA 12-24mm f/4, and Sigma AF 10-20mm f/4-5.6. Is there any other lens on the market i should consider? Does anyone have experience with any of those two lenses? Pros & Cons, recommendations, sample shots would all be appreciated! Thank you!