RF 35/1.8 for astrophotography

[AJ]

I am looking for a 35 mm lens for astrophotography. I've been looking at RF 35/1.8, but the sticking point is coma/astigmatism which is severe wide-open.
But ... does this problem go away when the lens is stopped down? For example, here is an aperture sweep of my RF 24/1.8 which has bad astigmatism wide open but produces nice results from f/3.5 and up.



I shoot with a star tracker so f/4 is not a big deal.
I know that there are other lenses out there that have well-controlled astigmatism wide open: EF 35/1.4 L mk2, Tamron 35/1.4 di USD, Sigma 28/1.4 Art. But these are big and heavy lenses, and I'd love to have a small, nimble little lens, particularly for other uses. RF 35/1.8 has a lot going for it: nice bokeh, close focusing, sharp, lightweight, punchy colors, small, great price. There is just the astigmatism problem. Does RF 35/1.8's astigmatism problem go away when stopped down? Is there an aperture sweep out there that anyone can point me to? Usually I look at Lenstip for that, but they don't have a complete review of this lens.
One more thing. Does RF 35/1.8 have field curvature? Field curvature and astro don't go together very well. I've been burned by that before with other lenses.
Thanks.

 

[Frodo]

I compared astro performance of a friend's RF 35/1.8 with my EF 35/2 IS and RF 24/1.8. I can post the results in 4 weeks when I'm back home. But here is a comparison of the EF vs RF 35mm at f/2.8 (not a perfect comparison as I misfocused the RF and had to reshoot). But the difference was quite dramatic.

 

[AJ]

I compared astro performance of a friend's RF 35/1.8 with my EF 35/2 IS and RF 24/1.8. I can post the results in 4 weeks when I'm back home. But here is a comparison of the EF vs RF 35mm at f/2.8 (not a perfect comparison as I misfocused the RF and had to reshoot). But the difference was quite dramatic.

Wow is it ever a dramatic difference. The EF 35/2 turns stars into albatrosses migrating away from the center of the image. An interesting effect for sure, but not exactly what I'm looking for. I look forward to your results - thanks!

 

[SwissFrank]

The Sigma 28/1.4 seems to have no coma whatsoever wide-open. I think the Sigma 24/1.4 had bad coma though. There's definitely a good vid comparing the two lenses with side-by-side pixel-by-pixel comparison about half-way through the vid. It's the only non-Canon lens I've bought ever since switching to Canon in 1996, and really the only lens I use the EF adapter for. (I had 15 EF lenses when I got my EOS R, but just about never used the old lenses on the new body.) It is massively discounted at Adorama periodically--sometimes mentioned on this site but sometimes not, so don't rely on seeing a mention here.

 

[Frodo]

Here are some comparisons of the EF and RF 35mm lenses, and the RF 24mm, all at f/2, 2.8, 3.5 and 4. Not sure what the magnification is, but about 1/6 of both dimensions of the full frame.

 

[AJ]

A belated Thanks for this! It looks like the RF 35/1.8 coma and astigmatism problems go away between f/2.8 and f/3.5. Behaviour not unlike the 24/1.8.