What is the best wide-angle landscape lens for Canon R5?

Regarding what #1 said about "> Im seeing weird smearing in the corners..." - yeah, that high res R5 sensor is brutal on old glass. Since youre heading to the Dolomites, you basically need native stuff to get the most out of those 45 megapixels. TL;DR: Buy the Canon RF 14-35mm f/4L IS USM. Its lighter, cheaper, and wider than the f/2.8 version. Heres the practical breakdown:

• Canon RF 15-35mm f/2.8L IS USM: Top-tier lens. Great for astro, but heavy and uses your whole budget.
• Canon RF 14-35mm f/4L IS USM: Best for hiking. That 14mm wide end is killer for big mountains. You dont really need f/2.8 for standard landscapes.
• Laowa 15mm f/2 Zero-D for Canon RF: Very sharp prime and way cheaper, but its manual focus only. Id grab the 14-35mm and use the leftover cash for travel expenses.

> Im seeing weird smearing in the corners at f/11 that I never noticed before. Tbh that smearing is a classic symptom of using older EF glass on a high-res sensor like the R5. Those 45 megapixels are totally unforgiving and really show the limitations of older designs. I have been using the Canon RF 15-35mm f/2.8L IS USM for over a year now and I am incredibly satisfied with the results. It is easily the best wide zoom I have ever owned for landscape work. The reason this happens is basically the light angle. With the native RF mount, the lens sits much closer to the sensor, allowing the rear element to be larger. This means light hits the corners of your sensor at a much straighter angle than an adapted EF lens ever could. That is what fixes the corner mushiness and chromatic aberration you are seeing at the edges.

• Sharpness: It is tack sharp across the frame even at f/2.8, which is pretty rare for a zoom.
• Handling: It balances perfectly on the R5 body without the clunky adapter weight shifting everything forward.
• Stabilization: The IS works well with the IBIS for handheld blue hour shots when you dont want to set up a tripod. I used this setup for a mountain trek recently and the files were just flawless. While some folks like the Canon RF 14-35mm f/4L IS USM for being lighter, the 15-35mm is the better pro choice for that 45MP sensor. Since you are doing the Dolomites, you are gonna want that f/2.8 for the extra drama and low light capability. Just go for it, you wont regret the investment.

Honestly, save your money and grab the RF 14-35mm f/4L. I switched from the EF version too and I am very satisfied with how it handles the 45MP sensor. Since you are doing landscapes, you really dont need that f/2.8 aperture anyway. Reasons it works well for me:

• 14mm gives you that extra bit of width for those huge mountain vistas
• It is way lighter for those long Dolomites hikes
• Uses 77mm filters so you dont need a massive new holder system
• Hundreds of dollars cheaper than the 15-35mm I have no complaints about the image quality. Tbh, the software correction for distortion is a bit heavy at 14mm, but the end result is clean and sharp. You will have plenty of budget left over for your trip and still get better corners than the EF glass could ever give you on that body.