Originally posted by PJ1 Hi Jim. Another welcome from Australia. Good luck sticking to just two lenses. Unless you are super-human, the Forums will reshape your wants and needs very quickly.
Hi PJ1. Since I joined I've been doing a ton of research about what appears to be a "unicorn" lens...a beautiful fictional creature. I don't want much; just perfection ;-) Anyway, I need a lens that is f2.8 at the slowest, ultra wide (12mm to 15mm), tack-sharp across the entire frame, minimal distortion and CA, and costs less than $500 US. A Pentax/Ricoh-built lens is preferred, but I've owned other brands over the years and I'm impressed with Sigma and Tokina. I've never owned (or afforded) Zeiss or any of the other German lenses.
I will be using it primarily for wide vista landscapes (Grand Canyon, for example) and astrophotography. While I'm in Arizona, I can't pass up the chance for Milky Way shots in the clear desert night air.
The 20-40mm is not wide enough for me, both for landscape and astro work. I've been looking deeply at the Sigma 17-70mm f2.8 to 4 (the new generation), but it suffers from softness and significant CA and distortion. The Tamron 17-50mm f/2.8 XR Di-II LD appears good, and it's more affordable, but it has wonky focusing problems with accuracy and inconsistency. It would be too unreliable as my primary glass.
Unfortunately, my original option of the Pentax 14mm f2.8 has too many poor professional reviews. The other lens I was looking at, the Pentax 50mm f1.8, is still a viable option for me, though. Like I said earlier, I won't be shooting much at 75mm (equivalent).
So I'm still looking for that WA lens. Maybe I'll use different unicorn bait, or a bigger net. Any advice from users of WA lenses with the K-70, used for landscape and astrophotography, would be greatly appreciated.