This ^

Seconding the recommendation above! Honestly, after years of shooting wide fields, I've found that the Sigma 28mm f/1.4 DG HSM Art for Canon EF is the real sweet spot for the Ra's sensor. It's much cheaper than RF glass and the edge-to-edge sharpness is incredible at f/2.0. If you're on a tighter budget, the Samyang 14mm f/2.8 ED AS IF UMC for Canon EF is a classic value pick, though teh corners can be a bit hit-or-miss. Hope this helps!

Regarding what #10 said about the Sigma 40mm, I honestly couldnt agree more. That lens is in a league of its own for star fields. I stumbled upon this discussion and felt like I had to weigh in since I have been shooting with the Ra since it dropped. While the 40mm is unmatched for sharpness, sometimes you just need a wider field. Here are a couple of other options that have kept me satisfied:

• Canon RF 28-70mm f/2L USM
• This is my go-to for versatility. It handles coma way better than the 15-35mm and the f/2 aperture is plenty for deep sky.
• Voigtlander Nokton 50mm f/1.2 Aspherical
• If you want something manual and tiny, this thing is beautiful. Stars stay pinpoint even wide open. I really like the Sigma Art series, but the native RF glass has been much more reliable for my workflow lately. No complaints with the optics on either of those.

Seconded!

@Reply #6 - good point! Honestly though, I've had some pretty frustrating issues with those big adapted setups on my Ra. The balance is just wonky. It makes the whole rig feel way too clunky for long nights out there. Unfortunately, the sharpness at the edges on those older lenses just hasn't been as good as I expected once you really zoom in. Kinda disappointing tbh.

• Honestly, just go with Canon, you cant go wrong with their native stuff.
• Stick to the native mount glass if you want to avoid adapter issues.
• Look into the newer manual lenses from some of the boutique brands. Its a letdown that the expensive glass still has these quirks. Staying with the same brand usually fixes most of the headache though. Just keep looking at the native options and you'll find something much more reliable for your setup... it's out there!

To add to the point above: it seems like everyone is torn between the heavy Sigma Art glass and native RF options. I have been following this thread since yesterday, and honestly, the reliability of your rig is just as important as the corner sharpness. Don't underestimate how much stress those heavy EF adapters put on your mount over long, cold nights.

• If you are worried about weight and balance, maybe look at the Canon RF 35mm f/1.8 Macro IS STM. It is way lighter, and while it is not f/1.4, the star shapes are surprisingly clean for the price.
• Just be careful with third-party lenses if you plan on doing lots of firmware updates on the Ra. I had a buddy run into communication glitches with some older adapted glass, so make sure to check compatibility reports first.
• If you really need that wider look but want to avoid the coma issues people mentioned, the Canon RF 16mm f/2.8 STM is super cheap and small. It is not perfect, but it is a safe, reliable backup that wont stress your tripod head.

+1

🙌

Wait really?? Thats actually super helpful. I always thought it was the other way around.

In my experience, you should definitely watch out for the Canon RF 15-35mm F2.8 L IS USM if you're chasing f/1.4 level sharpness. It's a great lens, but for the Ra's sensor, the coma at the edges can be frustrating for the price. Honestly, I've had the best luck with the Sigma 14mm f/1.8 DG HSM Art for Canon EF using the adapter. It’s heavy and pricey, but the light gathering is unreal for those H-alpha regions! Hope this helps!

Saved for later, ty!

To add to the point above: after years of testing glass on modified bodies, I really think people sleep on the Sigma 40mm f/1.4 DG HSM Art for Canon EF. I know, it sounds a bit narrow for wide-field, but the lack of coma is just breathtaking. Its easily the sharpest lens Ive ever put on my Ra. Most wide lenses get mushy in the corners but this one stays tack sharp even at f/1.4. It basically turns your camera into a mini telescope. If you are dead set on something wider for those massive Milky Way arches, the Sigma 20mm f/1.4 DG HSM Art for Canon EF is still the one to beat. Youll need the Canon Mount Adapter EF-EOS R obviously, but native RF options just havent caught up to these specific Art primes for pure astro performance yet. The 20mm has some slight vignetting wide open, but the star shapes are way better than what you get on the zooms. TL;DR: Grab the Sigma 40mm f/1.4 DG HSM Art if you want the absolute best star quality and dont mind stitching panoramas. Its a heavy beast, but the optics are flawless for H-alpha regions.

> Most wide lenses get mushy in the corners but this one stays tack sharp even at f/1.4. Like someone mentioned, corner performance is the real bottleneck with these high-resolution sensors. I struggled with this for months when I first picked up my modified body. I went through three different fast primes trying to eliminate that pesky aberration, but honestly, the field curvature on most fast glass just doesnt pair well with the sensor stack. Be careful if you are buying used, as internal alignment issues can really throw off your focus across the frame. I found that even with my current setup, micro-adjustments are mandatory. I would suggest spending extra time checking your back-focus. It took me a dozen sessions to realize it was my technique, not the glass, that was ruining those long exposures. Just make sure to verify your infinity focus settings every single night, or you might find yourself with a pile of soft, unusable shots after a long hike.

👆 this