CCD imaging resolution of large atm scopes?

Hi all...

Was pondering my future retirement dreams and visions of a large telescope and
observatory in some reasonably dark location in the southeast...

By large I mean something in the 24 to 40 inch class....

Now it is apparent from some of the CCD pics amatuers have taken of the planets
with more modest size scopes that they are able to reach darn close to the
theoretical limits of resolution and contrast...ie in the .5 to .25 arc second
range....

Butttt....these result from several things.....first modest size scopes ( 8 to
16 inches).....secondly...they can image for hours, days, even weeks to get a
good planetary shot.....and thirdly....they take many FAST images where they
"freeze" the seeing, pick the best looking of some fraction of them, and then
combine that fraction for a final image....

Back to the large dream scope....lets say Im not really interested doing the
planet imaging thing....Im more interested in CCD photometry, asteroid
searches/astrometry, nova patrol, faint comets etc etc......now this kind of
work (if your looking to be at all efficient about it) requires long exposures
per frame...and the ability to use the majority of the frames taken....so now
in addition to having a scope 2 to 5 times as large as what the planetary
imagers use we also have the exact opposite in terms of exposure duration and
required fraction of usable frames....

Sorry, getting to my point here....now I find it hard to imagine if I built a
40 inch scope and it was located somewhere near sea level in the southeast USA,
that I would get anything remotely close to .1 arc second star images on CCD
frames ranging anywhere from 30 seconds to many minute exposures (and lets
assume seeing is our only problem....other problems such as tracking, scope
vibrations, tube currents, overly warm observatory etc etc have been
eliminated)....

Now, my WAG is that such large scopes probably dont exceed .5 arc seconds
imaging give or take the majority of the time...if that good...

Anybody here with relatable experience or other WAGS?

take care

Blll

BllFs6 wrote:

Hi all...

Was pondering my future retirement dreams and visions of a large telescope and
observatory in some reasonably dark location in the southeast...

By large I mean something in the 24 to 40 inch class....

Now it is apparent from some of the CCD pics amatuers have taken of the planets
with more modest size scopes that they are able to reach darn close to the
theoretical limits of resolution and contrast...ie in the .5 to .25 arc second
range....

Butttt....these result from several things.....first modest size scopes ( 8 to
16 inches).....secondly...they can image for hours, days, even weeks to get a
good planetary shot.....and thirdly....they take many FAST images where they
"freeze" the seeing, pick the best looking of some fraction of them, and then
combine that fraction for a final image....

Back to the large dream scope....lets say Im not really interested doing the
planet imaging thing....Im more interested in CCD photometry, asteroid
searches/astrometry, nova patrol, faint comets etc etc......now this kind of
work (if your looking to be at all efficient about it) requires long exposures
per frame...and the ability to use the majority of the frames taken....so now
in addition to having a scope 2 to 5 times as large as what the planetary
imagers use we also have the exact opposite in terms of exposure duration and
required fraction of usable frames....

Sorry, getting to my point here....now I find it hard to imagine if I built a
40 inch scope and it was located somewhere near sea level in the southeast USA,
that I would get anything remotely close to .1 arc second star images on CCD
frames ranging anywhere from 30 seconds to many minute exposures (and lets
assume seeing is our only problem....other problems such as tracking, scope
vibrations, tube currents, overly warm observatory etc etc have been
eliminated)....

Now, my WAG is that such large scopes probably dont exceed .5 arc seconds
imaging give or take the majority of the time...if that good...

Anybody here with relatable experience or other WAGS?

take care

Blll



Bill,
The atmospheric limitations on long exposures are quite variable and 1
arc sec would usually be considered quite good. Using the quality of
planetary images as a guide the best skies (for seeing) in the US are in
south Florida and texas Texas. Of course there is the adaptive optics
route to higher resolution.

Dave