Jeff
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Jeff wrote:
It was indeed interesting enough to try... and then return due to the marginal corners. 28/1.4 Art is the lowest I'd go.
kirbic wrote:
Certainly not going to shoot the 20/1.4 Art at f/1.4 - yes, the corners get a bit bad. I have found, however, that by f/2 things are pretty good, and a 20mm f/2 astro lens is something that we could only dream about just a decade or so ago.
I did not find it pretty good (nor even OK) at f/2, which was the problem (most 'astro' lenses need to be stopped down to at least ~f/1.8 or so to get adequate corners). I found it clears up around f/2.5, at which point it had virtually zero value over just using the Tamron 15-30/2.8, which is actually quite a good lens and can be used wide open, as well as giving additional flexibility for composition. Of course, the 20 Art is otherwise a great lens.
Perhaps I got a bad one, but I did subsequently also try the 24 Art and returned both for the same reason(s); unfortunate because either could be a useful lens. I'm pretty far down the rabbit hole of these kinds of lenses, though, so my expectations are quite high in regard to corners. Since getting a tracker I really only use anything less than 28mm for timelapses, and almost always choose the lens based upon how much time I have to capture a scene before I need to move on for a variety of reasons (e.g. to capture a different scene, timing of an astro event, incoming clouds/weather, impending dawn/moonrise, etc.).
Sigma's 20, 24 and 85 can be made better if Sigma so chooses (mostly by increasing size of the lens; 85 would just need an optical re-design/tweak). I actually find it quite amusing that Canon is finally, after all these years, following Sigma's lead and starting to produce lenses that can be used for serious astro. The amusing part is, after migrating to the R platform which promised more compact cameras and lenses, they flout the trend and produce beasts like the RF85/1.2 (a positively stellar lens) and RF28-70/2 (can't speak to it for astro, was probably designed for video). I really hope they continue the trend with a 35 or 28/1.2 (!), as well as a 16 or 20/1.4 lens. I won't hold my breath, but I bet they come out with something usable in that range in the next year or two.
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