EOS Ra: A great Full Frame Astrophotography mirrorless camera...

First up: The cause of the vignetting with the EF 24mm f/1.4L II USM lens:
I made two local attempts to test this lens again but I live in the suburbs and there's so much light coming off the clouds after the moon set that I simply can't expose for similar exposure times to conduct a test with and without the lens hood in place.  Until the weather clears and I can get to a dark-sky location again, I can't even test the camera with similar conditions/settings.  A 15 second exposure at f/1.6 and f/2 with ISO 1000 was unable to even coax out any hint of a vignette.  I will have to wait for another clear night with no moon.
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Last night I drove up to the mountains and took more shots with the Canon EOS Ra camera. These are really just early tests for me.  I'm really just limited by the lenses I'm using and those offer me either 10 second (max) exposures at 50mm and 20 second (max) exposures with the 24mm lens.  Any longer and I'll be getting obvious star trails without an EQ mount. The Auto WB also meant inconsistencies with sky shots based on other factors.  Again - these are simply test shots with minimal effort.I'm not going to edit anything properly until I get to refine the procedure in a future shoot. I'm sure all you RAW shooters will still have a keen edge on this, regardless.
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EOS M6 - Someone has recently graded the road onto the mountain ridge I was heading to.  Whoever that was: Thank you!.  I couldn't risk my non-offroad car on the old road.

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The camera was VERY easy to use in the dark and although it meant nearly 4 hours of driving at night to get there and home again, I had to time my arrival with the setting of the moon.  Someone had graded the dirt road leading into the National Park and that meant a bunch of carvans and cars parked where I usually set up.  I ended up lugging my gear to a mountain ridge in the dark and regretted leaving my hat with the LEDs in the brim at home.
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The shots I took are simply JPEGs.  I'd normally edit these JPEGs to increase contrast and bump up colors but this time I increased the Saturation in the "Fine Detail" User Defined Setting and then promptly forgot that I had calibrated my camera's Custom White Balance by shooting a white card in sunlight at midday.  That's pretty embarrassing and it meant that I had different colors to contend with than expected. 
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EOS Ra + Canon EF 50mm f/1.2L USM lens - quick test to see how the AF on the R worked with such a tricky and thin DOF with this lens... (which is notoriously fickle to work with).  My target was the second pencil from the left and the image was taken at MFD.  The lens works just fine with the Ra.

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Second Night Shooting with the EOS Ra.
This was much easier because I was now familiar with my settings and what to expect from the camera.  Again, the 30x magnification on the LCD made it so easy to manually focus the lenses I was using.  I often refocus a lens just to be sure I would nail a shot but virtually every shot was sharp, with only very slight movement on the stars.  The lenses I was using both produce chromatic aberration and coma ...plus light-falloff (on the 50mm)... and hard vignetting on the 24mm lens, just like the previous evening.  With a tracking mount I can use smaller apertures to cut out most of those issues.  These are lens limitations and have nothing to do with the camera.
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EOS Ra - my view South at night.  The Magellanic clouds can be glimpsed here (the LMC is slightly cropped on the right).  The light from the left is from the city of Sydney.  The lights on the right are from the city of Blackheath.

EOS Ra - Looking North from my position.   This is a dual exposure/composite.  The "swirl" was caused by not screwing down the  pivoting head on my tripod during a 10 second exposure.  The camera slowly turned on the tripod for the duration of the first exposure. I didn't want to throw the shot out so I used it here since my foreground wasn't all that interesting.  Milky Way colors were not enhanced.

EOS Ra LCD during playback - you can see the colors in the JPEG as presented by the camera after taking the shot.  This is literally what the camera is producing and displaying.

EOS Ra - My view North East from where I was set up.  I just took this one randomly while waiting for some clouds to move.

EOS Ra + Canon EF 50m f/1.2L USM lens - three merged JPEGs with light-falloff removed.  Plenty of coma swirling around here from the lens used.  Colors haven't been tweaked.  It's essentially the JPEGs that came out of the camera.  These are simply test shots so I haven't bothered to edit them at this stage.

EOS Ra + Canon EF 50mm f/1.2L USM lens - JPEG from the camera - taken with the 50mm lens.  These are the colors captured by the camera.  I simply made a light adjustment to the "Levels" in Photoshop to increase the contrast and lift the colors slightly.  I used to spend hours trying to bring out these colors and contrast from shots with other cameras.  WB is still set to Auto here.

This is the LCD of the Ra again, this time showing the LIVE view of the the Milky Way.
EOS Ra + Canon EF 24mm f/1.4L II USM lens. - JPEG from the camera using the Auto WB setting. Vignetting was reduced in Lightroom and cropped out by Photoshop..  A very slight increase in saturation was added - just to see what the camera had pick up.  This odd magenta/teal hue is presumably from my Auto WB choice.  I'm certainly picking up colors that I don't get from non-modded cameras.

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Thoughts...
My thoughts after spending more time with the camera is that it's really quite a versatile alternative to the other conventional choices. Obviously I messed up again by forgetting to use the Custom WB and only discovered this oversight when I was reviewing the images at home with friends.  As a camera for use at home, it's actually more fun to use that a DSLR and only slightly more arduous than using a Canon EOS M-type mirrorless camera. I took some pictures of my pets when I got home and that narrow FOV from the 50mm lens I was using nailed the shots in an instant.  Battery Life is great. I like the button placement. Not sure I needed the Control Ring variant of the lens adapter as the "normal" version would have worked fine at a lesser price.  I found the -6EV was effective at nailing focus in virtual darkness when required.  I may need to bump down the color (saturation) setting on the Ra camera slightly - after lifting it a notch for these shots.
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'll be sure to pop back to this thread after confirming whether or not the Lens Hood is contributing to the vignetting by the 24mmL lens.  I'm quite sorry I am unable to put that mystery to rest sooner.