Careful: dont chase max aperture—corner coma wide-open will wreck stars. I’d start with a 20–24mm fast-ish wide (f/1.8–2.8) and stop to ~f/2.8–4; cleaner corners, easier 500-rule, way less pain.

Oh man, been there — when I got into Milky Way stuff I also assumed “fastest lens wins” and then the corners were… not great lol.

Quick question before I steer you: are you on the EOS Ra with the EF adapter already (so EF lenses are fine), or are you trying to stay native RF only? And do you care more about wide landscapes (14–16mm vibe) or a tighter MW core (20–24mm)?

If EF is ok, in your budget I’d look at:
- Sigma 14mm f/1.8 DG HSM Art for Canon EF (insanely bright, but heavy)
- Sigma 20mm f/1.4 DG HSM Art for Canon EF (nice compromise, stop to f/2)
- Canon EF 24mm f/1.4L II USM (used, classic astro option)

Lesson learned: I pick “clean corners at f/2–2.8” over “f/1.4 bragging rights” every time. whats your usual foreground style?

- Just catching up on this thread — I went through this last year w/ a similar setup (full-frame astro body + tripod, no tracker), and I totally fell into the “f/1.8 solves everything” trap. Spoiler: it didnt lol.
- What surprised me most: corner coma/astigmatism mattered WAY more than center sharpness. I had a fast wide zoom and a fast prime, and the prime was “brighter” on paper, but wide open the corners turned stars into little seagulls. I ended up shooting it stopped down anyway, so the extra speed was kinda wasted.
- I’m not 100% sure this is universal, but IIRC once I stopped obsessing over f/1.8 and started treating $$f/2.8$$ as my “real” working aperture, my keepers shot way up. Cleaner corners, easier processing, and less time swearing at the edges.
- Cost-wise: I kept trying to save money by buying the absolute fastest thing, then I spent more later swapping around. In hindsight, paying for better corner behavior (even if it’s only “fast-ish”) was the value move.
- Practical tripod tip: I basically lived around 14–24ish mm, timed exposures conservatively (shorter than the rule-of-thumb), and just accepted higher ISO + stacking later. The EOS Ra RAW files handle that pretty well imo.

good luck, been there 🙃

For your situation, I’d suggest a **quality wide prime in the ~20–24mm range** from Canon or Sigma (or similar). Background: on the EOS Ra, stars show every flaw. Why it matters: **coma/astigmatism in the corners** is what makes “clean stars” or a smeary mess, not just f/1.8. So yeah: buy for **corner performance**, shoot **wide-open only if it’s clean**, and plan to stop down to ~f/2.8-ish on a tripod. Also safety-first: dont go super heavy on a basic tripod, wind is brutal idk... good luck

Saw this earlier—if I were buying *one* “keep it for years” astro lens for the Ra in ur budget, I’d go Canon RF 16mm f/2.8 STM + spend the rest on a small tracker later. It’s not the sexiest spec sheet, but it’s light, cheap (~$250), and I’ve found it’s easy to live with long-term because it actually gets used for daytime too. If you want the nicer “forever” option in that $600–$900 window, Samyang/Rokinon AF 14mm f/2.8 RF is kinda the sleeper: wide enough that you can run longer exposures on a tripod before trails, and the frame looks more “night landscape” than 20–24mm. Practical step: on the Ra I always do a quick focus check at 10x live view, then lock focus with gaffer tape—temperature drift is REAL. Also enable the Ra’s interval timer and shoot 10–20 frames to stack; it’s the biggest quality jump without changing gear tbh.

- Just catching up on this thread — I went through this last year w/ a similar setup (full-frame astro body + tripod, no tracker), and I totally fell into the “f/1.8 solves everything” trap. Spoiler: it didnt lol.
- What surprised me most: corner coma/astigmatism mattered WAY more than center sharpness. I had a fast wide zoom and a fast prime, and the prime was “brighter” on paper, but wide open the corners turned stars into little seagulls. I ended up shooting it stopped down anyway, so the extra speed was kinda wasted.
- I’m not 100% sure this is universal, but IIRC once I stopped obsessing over f/1.8 and started treating $$f/2.8$$ as my “real” working aperture, my keepers shot way up. Cleaner corners, easier processing, and less time swearing at the edges.
- Cost-wise: I kept trying to save money by buying the absolute fastest thing, then I spent more later swapping around. In hindsight, paying for better corner behavior (even if it’s only “fast-ish”) was the value move.
- Practical tripod tip: I basically lived around 14–24ish mm, timed exposures conservatively (shorter than the rule-of-thumb), and just accepted higher ISO + stacking later. The EOS Ra RAW files handle that pretty well imo.

good luck, been there 🙃

🙌

Just saw this today - honestly before you drop 900 bucks you gotta consider where youre actually shooting. Are you in like a Bortle 1-2 area or closer to a city? Because light pollution is going to dictate your signal-to-noise ratio way more than a tiny bit of coma will. Also ngl do you plan on printing these large or just for web? Tbh for the best performance-to-dollar ratio:
- Go with a third-party brand like Samyang or Rokinon
- Any of the newer wide primes from Sigma are usually solid for astro testing
- Just get a decent EF-to-RF adapter if you dont have one Afaik most of the serious benchmarks for astro favor these brands for corner consistency over the budget-tier native glass. You basically cant go wrong with any of their fast primes if you check the raw samples first.

For your Canon EOS Ra, the best single lens is the Sigma 28mm f/1.4 DG HSM Art with an EF-to-RF adapter. This lens has emerged as a favorite among EOS Ra users for Milky Way and wide-field astrophotography

Ugh, im in the exact same spot right now and honestly its been pretty discouraging. Just got my Ra and ive been struggling to find a lens that doesnt make the stars look like little boomerangs in the corners. I feel like ive wasted so much time testing stuff and still havent found the one.

• Canon RF 16mm f/2.8 STM: Its super light and cheap which is nice, but unfortunately the corners are just a mess of distortion on the Ra sensor.
• Samyang AF 14mm f/2.8 RF: Gives a really great wide view, but I had huge issues with quality control and the stars were never truly sharp for me.
• Canon RF 35mm f/1.8 IS Macro STM: Nice and fast for low light, but not as good as I hoped for astro because the coma is pretty noticeable wide open. Tbh it feels like this camera is so good that it just exposes every tiny flaw in glass. Im still hunting for something that actually works... let me know if you find the magic bullet because I sure havent yet.