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Buying an SCT



 
 
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  #1  
Old January 22nd 05, 06:20 AM
Larry G
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Default Buying an SCT

On Fri, 21 Jan 2005 22:41:37 GMT, SCT Buyer wrote:

I'm going to buy an 8" SCT in the next month or so, but am undecided
if I should buy a Meade or Celestron.

Generally speaking, which of the two tends to be better optically and
mechanically? I can't afford to buy a new scope very often, so I want
my decision to be an informed one.



I've owned two SCT's, both 8". The first was a Meade 2080 (circa 1982).
The optics were (apparently) exceptional for a mass production SCT. The
Encke Division (Minima, for you purists) was visible nearly the entire
circumference of the rings. It had an oversized primary, and smooth
focusing.

Tnen, in the late 1990's, I picked up a used Celestar with StarBright
coatings (made around 1992?). Optically, it never performed as well
as the Meade, but on occassion, delivered some of the best images of
Jupiter I've seen, though not as good on Saturn! And, under dark skies,
it provided a very pleasing view of M51.

It is unwise to make too much of these annecdotal comparisons because
the observations were made years apart, in different locations, under
different condition, and are subject to the frailties of human memory.

It is my understanding that the newer Meades have stepper motors which
make an awful racket under the most peaceful skies. And Celestron's
single armed fork isn't stable enough for serious long exposure
photography. However, the larger Celestron scopes (esp. 9.25") are
rumored to have excellent optics these days.

Your best bet may be to buy according to features, from a company which
will allow generoust test time and exchange rights. Then, test the
dickens out of which ever you choose to see if it lives up to expectation.

Cheers, and good luck,
Larry G.

  #2  
Old January 22nd 05, 06:30 AM
Chris L Peterson
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On Fri, 21 Jan 2005 23:20:12 -0600, Larry G wrote:

It is my understanding that the newer Meades have stepper motors which
make an awful racket under the most peaceful skies...


Meades use DC servo motor drives (and have for as long as they made DC units,
AFAIK). The drive systems perform very well, but are noisy. The newer units are
somewhat quieter. The default high slew rates should be slowed down a bit to
make operation quieter, and in all likelihood to significantly increase the
mechanical life of the scope.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com
  #3  
Old January 22nd 05, 09:30 AM
David Nakamoto
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The last time I checked, if you go with a GOTO, the Meade may have more objects
but the Celestron is quieter. I like the packaging better on the Celestron, but
this is subjective.

Optically and mechanically, because they're mass produced, you have a spread of
quality, and the mean or center of the spread is pretty much the same.

Personally, my experience with their electronic or computer technical support
departments is heavily in favor of Celestron, but others have reported
differently.

Good Luck !
--
Sincerely,
--- Dave
----------------------------------------------------------------------
It don't mean a thing
unless it has that certain "je ne sais quoi"
Duke Ellington
----------------------------------------------------------------------

"SCT Buyer" wrote in message
...
I'm going to buy an 8" SCT in the next month or so, but am undecided
if I should buy a Meade or Celestron.

Generally speaking, which of the two tends to be better optically and
mechanically? I can't afford to buy a new scope very often, so I want
my decision to be an informed one.



  #4  
Old January 22nd 05, 11:25 AM
Roger Hamlett
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It is my understanding that the newer Meades have stepper motors which
make an awful racket under the most peaceful skies. And Celestron's
single armed fork isn't stable enough for serious long exposure
photography. However, the larger Celestron scopes (esp. 9.25") are
rumored to have excellent optics these days.

Both the Meade units, and the Celestrons, use servos. The difference is
that on the Celestron NS family, these are professionally made industrial
servo systems. On the Meades, the older units used what were basically
'slot car' motors, and mouse encoders for the position, the latter units
have retained the mouse encoders, but switched to slightly improved
motors. The Celestron motors are more accurate, and smoother/quieter,
_but_ they still have the downside, of no working PEC, in the NS units...
I posted the following in answer to an almost identical question about
'which is best', on another group, and think it is close to saying it
all...

It is difficult.
I have had a number of scopes from both manufacturers. Generally, in the
last few years,I have allways found the Celestron optics to have the
slight 'edge' (some of the earlier units were 'dogs'). Apparently this may
be down to a fractional difference in the way the correctors are
fabricated, giving slightly less chromatic aberration. However on all the
modern scopes, both are pretty good.
Mechanically, the Meade, has the better external 'finish', with nicer
shaped knobs and handles, and surface detailing. Internally, the Celestron
has the better drives on the NS models in particular. The Meade has more
'frills' in the hand controller, but in use, both work well, and point to
the objects you want, with the NS, being slightly quieter.
The Celestron scopes are easier to 'handle' for a given size. The actual
lifting handles work, while the Meade ones are poorly placed.
Currently, on the Celestron NS models, PEC, still does not work. However
their drives are enough better, that tracking is still very good. It is
though a very 'silly' missing feature.
I 'prefer' Celestron, having had better performance, and experience with
servicing from them. However that being said, I'd say that (perhaps
unfortunately), it is down to the 'deal' you can get. I suspect you will
be able to afford more 'extras' with the Meade, than the Celestron unit.
There is also the problem, that these 'bundles', are so cheap, that it
makes other routes look expensive. For instance, as a small SCT, with a
'great' mount, I'd say the combination of a third party mount (the GP-DX
for smaller scopes, and the G-11 for heavier units), with a Celestron OTA,
is really nice, but the price of this type of setup is far above what you
can buy a bundled scope, mount, and controller for...
Take your time, see if you can actually 'see' the scopes you are
considering, before spending your money.
Both makes are phenomenal value for money, with an 8" SCT, and mount, with
very competent optics, costing less, than I paid to make an 8" Newtonian,
with basic clock drive, some years ago.

Best Wishes


  #5  
Old January 22nd 05, 09:32 PM
Matthew Ota
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Based on experience, I would give the nod to Meade for excellence in
service alone.

Matthew Ota

SCT Buyer wrote:
I'm going to buy an 8" SCT in the next month or so, but am undecided
if I should buy a Meade or Celestron.

Generally speaking, which of the two tends to be better optically and
mechanically? I can't afford to buy a new scope very often, so I want
my decision to be an informed one.

  #6  
Old January 22nd 05, 10:28 PM
Too_Many_Tools
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Hi,

Could you expand on this comment with further detail ?

"The Celestron motors are more accurate, and smoother/quieter,
_but_ they still have the downside, of no working PEC, in the NS
units..."

And how Meade apparently has a working PEC?

I jsut bought a N11GPS so I am interested in your further discussion on
this subject.

Thanks

TMT

  #7  
Old January 22nd 05, 11:10 PM
Roger Hamlett
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Default


"Too_Many_Tools" wrote in message
oups.com...
Hi,

Could you expand on this comment with further detail ?

"The Celestron motors are more accurate, and smoother/quieter,
_but_ they still have the downside, of no working PEC, in the NS
units..."

And how Meade apparently has a working PEC?

I jsut bought a N11GPS so I am interested in your further discussion on
this subject.

Thanks

TMT

The motors in the Celestron, are industrial servo systems. These are quite
expensive assemblies with armatures designed to minimise 'cogging', and
give smooth responses. They are about 10* the price of the motors used in
the Meade scope!. They are quieter, and smoother than the Meade units.
However the biggest error for short durations on any scope, is surface
errors on the main gear, and the worm. A tiny misalignment of the shaft,
or a small error on the surface finish, translates into several arc
seconds of movement. The error in earlier gears in the drive is reduced by
the gear ratio after the gear. It is the final drive worm (because of it's
small diameter, relative to the main gear), which ends up introducing the
biggest error. Fortunately, the largest part of this error is 'periodic',
repeating each time the gear turns. In order to improve this, scopes
generally apply 'periodic error correction', where the movement of the
worm, is fractionally 'tweaked' to adjust for the errors. This feature,
has never (yet) worked on the Celestron NS scopes. However their
'uncorrected' error is typically a little less than on the Meade units,
and fortunately quite smooth (which allows guiding to correct it fairly
well). This is the cause of quite a bit of 'annoyance' to imagers wanting
to use the scope for long exposures, without having to rely too much on
the guiding. It is important to realise the difference about PEC, versus
correcting this with the guider. The guider is allways 'reactive', it can
only correct for an error that has occured. PEC, can be 'proactive',
correcting for the expected error as it occurs.

Best Wishes


  #8  
Old January 22nd 05, 11:17 PM
Rod Mollise
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Could you expand on this comment with further detail ?

"The Celestron motors are more accurate, and smoother/quieter,
_but_ they still have the downside, of no working PEC, in the NS
units..."



Hi:

The Celestron uses high-quality Pittman servos, though the lower quality motors
of the LX200 GPS certainly don't seem to hurt it. They do seem a wee bit
noisier. But the LX200s are quite accurate indeed.

As for PEC, no, Celestron's PEC is NOT working correctly. They are aware of the
problem, and are supposedly working it. I doubt it's a front burner thing,
though, as most folks seem to have got away from PEC and are tending to either
autoguide or stack short exposures, both of which are techniques that make PEC
a little less needed.



Peace,
Rod Mollise
Author of _Choosing and Using a Schmidt Cassegrain Telescope_
Like SCTs and MCTs?
Check-out sct-user, the mailing list for CAT fanciers!
Goto http://members.aol.com/RMOLLISE/index.html
  #9  
Old January 22nd 05, 11:58 PM
matt
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Default


Rod Mollise wrote in message
...

Could you expand on this comment with further detail ?

"The Celestron motors are more accurate, and smoother/quieter,
_but_ they still have the downside, of no working PEC, in the NS
units..."



Hi:

The Celestron uses high-quality Pittman servos, though the lower quality

motors
of the LX200 GPS certainly don't seem to hurt it. They do seem a wee bit
noisier. But the LX200s are quite accurate indeed.

As for PEC, no, Celestron's PEC is NOT working correctly. They are aware of

the
problem, and are supposedly working it. I doubt it's a front burner thing,
though, as most folks seem to have got away from PEC and are tending to

either
autoguide or stack short exposures, both of which are techniques that make

PEC
a little less needed.



Peace,
Rod Mollise


well, Celestron calls those Pittman servos "high quality". As far as
industrial grade servos, they're as lame as the Meade using Mabuchi toy
motors. They're low end motors, nothing high quality in them. Higher quality
than Meade due to metal gearhead instead of plastic , that's about it.
Same size but high quality servos would cost several hundred dollars apiece
, would be brushelss or coreless , the Pittmans are $10 each, the Meade are
$2 each.

best regards,
matt tudor


  #10  
Old January 22nd 05, 11:58 PM
matt
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Default


Rod Mollise wrote in message
...

Could you expand on this comment with further detail ?

"The Celestron motors are more accurate, and smoother/quieter,
_but_ they still have the downside, of no working PEC, in the NS
units..."



Hi:

The Celestron uses high-quality Pittman servos, though the lower quality

motors
of the LX200 GPS certainly don't seem to hurt it. They do seem a wee bit
noisier. But the LX200s are quite accurate indeed.

As for PEC, no, Celestron's PEC is NOT working correctly. They are aware of

the
problem, and are supposedly working it. I doubt it's a front burner thing,
though, as most folks seem to have got away from PEC and are tending to

either
autoguide or stack short exposures, both of which are techniques that make

PEC
a little less needed.



Peace,
Rod Mollise


well, Celestron calls those Pittman servos "high quality". As far as
industrial grade servos, they're as lame as the Meade using Mabuchi toy
motors. They're low end motors, nothing high quality in them. Higher quality
than Meade due to metal gearhead instead of plastic , that's about it.
Same size but high quality servos would cost several hundred dollars apiece
, would be brushelss or coreless , the Pittmans are $10 each, the Meade are
$2 each.

best regards,
matt tudor


 




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