Quote:
Originally Posted by alpal
Ground based scope can't pick up ultra violet &
I don't believe they can give large pictures all in focus
at
a resolution of better than 0.1 arc seconds.
They can only give that resolution for a pinpoint little picture -
like splitting double stars.
Correct me if I'm wrong.
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Fair point on far UV, but a dedicated platform like GALEX (maybe a bit bigger) would probably still be better for that than a broadband observatory like HST.
As for resolution and large pictures Suprime Cam on Subaru has 0.2" per pixel, (ie same as HST WFC/IR), but ten times the FOV, while its update, Hyper Suprime Cam, has a pixel scale of 0.17 arcsec/px over 1.5 degrees (versus 2.7 armin for WFC) [which is why its looking for Planet 9] while "the LUCIs" on LBT are 0.12"/px over 4'
in the infrared (HST WFC/UVIS does indeed have a 4 "centiarcsec" [lets make that a word!] pixel scale quoted but the recommendation to users is not to image above 0.4" resolution, although the default setting is still 0.2": the CCD's are now significantly degraded by radiation and this along with a suite of software processing tools are necessary to combat the decrease in charge transfer efficiency due to "the space environment") Also, LBT has a nicely stabilised high resolution spectrograph in the basement that's 6m long and doesn't need a crew of 4 qualified astronauts and a Canadarm to service
Of course such wide fields are possible because of 2-storey field flatteners and other things space telescopes don't have, (like 400 fibre heads feeding cryostat-housed instruments the size of minivans), so it's really mostly the "other things" than just a mirror and a camera that favour ground based observatories, though size does matter.
But as you pointed out, not for every job, true. Also I can't say big images are what I had in mind with my post, pretty as they may be. So I could be plenty wrong about how the 8m class ground based observatories compare...