Gotta agree that Sigma is killing it lately, but honestly, you don't even need to spend your whole $1500 budget to get great results on the S1R II. If you’re gonna be hiking or doing long exposures, definitely look at the Sigma 16-28mm f/2.8 DG DN Contemporary. I was skeptical at first since it’s not an 'Art' lens (wasn't sure if it could handle the 47MP resolution), but in real-world testing, the center sharpness is basically top-tier when you stop down. The best part is it takes standard 72mm front filters. Most ultra-wides need those massive, expensive 150mm filter holders, so this saves you a ton of cash and bag space. It’s sorta lighter too, which your back will thank you for on long trails. TL;DR: The Sigma 16-28mm f/2.8 DG DN Contemporary gives you 90% of the performance for like $900. Use the extra money for a killer filter set or a better tripod.

Panasonic 16mm-35mm f/4! Razor sharp. I used it for years capturing my vintage Mustang's glory. Amazing detail!

Consider Sigma 14-24mm f/2.8 DG DN. Aberration correction is superb; I'm happy with mine.

Sigma 14-24mm f/2.8 DG DN. Used market is your friend; can find it ~$1200.

Sharp wide-angle, huh? DIY lens calibration can sometimes help sharpness, but it's tricky. I've had issues with DIY on my S1R, honestly. For guaranteed results, consider a pro calibration service instead. Alternatively, the Sigma 14mm f/1.8 is usually pretty sharp out of the box. Worth a look before diving into adjustments!

Sigma's a contender! Research used prices; less depreciation risk, more lens for your buck!

Heads up on that wide angle! Consider a lens hood; prevents glare, sure, but also protects glass from flying rocks. Sigma 14mm f/1.8's a beast, but hood's crucial for safety!