I have been taking milky way panoramas, typically using 24mm or 35mm f/1.4 Samyang/Rokinon lenses, a Canon DSLR and a gigapan or roundshot motorized panorama head. At each position in the panorama I take multiple photos and stack them.
It has occurred to me that I would get better quality using longer focal length lenses - 50mm, 85mm or even longer. Obviously it will take more frames to get the same sky coverage, but the quality will be much higher.
Ironically, if you expose long enough to reach the same limiting magnitude, then my calculations show it can actually take less time to take a panorama with an 85mm than a 24mm. That's because light gathering power for astrophotos depends on the square of the clear aperture, not the f-stop.
You have to take more positions to get the same sky coverage, but need fewer shots to stack at each position.
My question is this - which short to medium telephoto lenses can be used wide open, or if not wide open, then how much do you need to stop them down?
Typically daytime photography treats the maximum aperture - i.e. wide open - as a bit of a desperation move, and the best quality occurs 1 or 2 full f-stops lower. However, every stop you stop down makes a lens less competitive for astrophotography.
That's usually not true for the fast telephoto sports lenses - like 300mm f/2.8 or 600mm f/4, which are typically used wide open, but those are too long for making panoramas.
Obvious candidates are:
Samyang/Rokinon 85mm f/1.2 XP/SP - I wonder what coma / edge quality is like at f/1.2 and f/1.4 or f/2?
Samyang/Rokinon 85mm f/1.4 - this is the ordinary, non premium version, presumably the SP/XP is better?
Sigma ART 85mm f/1.4 - I have no idea what it is like with respect to edge / corner quality
Zeiss Otus 85mm f/1.4 - I have tried this and it has way too much coma at f/1.4, less at f/2 but I am not sure even that is good enough.
Zeiss Otus 100mm f/1.4 - I haven't tried this one. But there is a lot of coma in the 55mm Otus, and 85mm so I am not hopeful
Sigma ART 105mm f/1.4 - I have seen photos online suggesting this needs to be at least f/2, and maybe more
Samyang/Rokinon 135mm f/2 - I have seen photos online that suggest it might be OK at f/2. If so it would be a great contender.
Canon 200mm f/2 - somewhat surprisingly to me, I have seen photos online suggesting this is very usable wide open. It's the baby brother to the 300mm f/2.8 so that might explain why it was built with good wide open performance.
I am open to other lenses too, so long as I can use with a Canon camera.