> Which one is actually gonna give me the sharpest corners for big landscape prints? I'd really suggest sticking with the native glass for a trip as big as the Dolomites. I learned the hard way when I took my Leica Super-Elmar-M 21mm f/3.4 ASPH out to the Alps a few years back. On paper, it is a legendary lens, but the SL2 sensor has a thick cover glass that just doesnt play nice with M-mount optics, especially wides. I ended up with these weird purple color shifts and soft corners that basically ruined my larger prints. You might want to consider the weight, but if sharpness is the priority, the Leica APO-Summicron-SL 21mm f/2 ASPH is the only way to go. It is corrected to a level that the M glass just cant touch because it is designed specifically for that digital sensor stack. Make sure to check your weather sealing too... the native SL lenses have those rubber gaskets which saved my gear when a sudden storm hit me near Seceda. With an adapted lens, you are leaving a gap for moisture to crawl into the mount. I wouldnt risk a brand new SL2 with an adapter in mountain weather tbh. Just be careful about the size tho, it is way bigger than the M version, but for prints, you wont regret the extra glass.

If you're heading to the Dolomites, you definitely want something that just works without a lot of fussing around with adapters or corner smearing. I personally prefer to stick with native L-mount glass because the communication between the lens and the body is just more reliable. Tbh, for a trip like this, you want that consistency and the peace of mind that comes with weather sealing.

• Leica APO-Summicron-SL 21mm f/2 ASPH: This is basically the pinnacle for the SL system. The APO correction means no color fringing at the edges, which is huge for those high-contrast mountain peaks. It is much heavier than the M glass, but the edge-to-edge sharpness is objectively superior on the SL2 sensor. No complaints about the build quality either, it works well in tough conditions.
• Sigma 20mm f/1.4 DG DN Art for L-Mount: I was actually quite satisfied with this for a more budget-friendly alternative. It is remarkably sharp in the center and holds up well in the corners once you stop it down to f/5.6 or f/8. It is bulky, though, so keep that in mind for long hikes.
• Panasonic Lumix S Pro 16-35mm f/4: If you want safety and flexibility, this is a solid choice. It's an L-Mount Certified lens so it feels very native and handles the 47MP sensor well. Corner sharpness is good, maybe not APO level, but very respectable for landscape prints. I would honestly go with the native SL 21mm if the budget allows. It just gives me peace of mind knowing the optics were designed specifically for that sensor. Its just safer... nothing worse than getting home and seeing soft corners on a once-in-a-lifetime shot.

TL;DR: Native glass is better but pricey. Unfortunately, the Leica APO-Summicron-SL 21mm f2 ASPH is overpriced. The Sigma 20mm f1.4 DG DN Art is way cheaper and its basically just as sharp.