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9.25 SCT, it ain't no planet scope

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#176 ensign

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Posted 29 October 2018 - 11:58 AM

No SCT's are  planet scopes. Always soft compared to a well built Newt.

I had an excellent 10” Newt.  I now have a 9.25 Edge HD.  IMHO, the views are at least as sharp in the cat as they were in the Newt.  I would go so far as to claim that the views are even better in the cat.  

 

I also have a “standard” C8 that gives soft views.  Because of this I don’t use this scope for visual at all, but it is fine for EAA.

 

I’ve done side by side comparisons with the Edge, properly acclimated, and my Equinox 120 on planets - in particular Saturn on a night of fair to good seeing.  I would say that it was a wash.  Both scopes delivered very good views.


 

#177 wargrafix

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Posted 29 October 2018 - 12:39 PM

Collimation is life. Just saying


 

#178 Magnetic Field

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Posted 29 October 2018 - 12:48 PM

Collimation is life. Just saying

But a miserable life. Just saying.


 

#179 skyjim

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Posted 29 October 2018 - 04:11 PM

Going back around 2010 I had a very good sample of a C9.25, a Intes Micro M703 and before all those nice cats a Skywatcher 120ED. First off the 120ED was a nice scope for good all around planetary views but the M703 cleaned its clock on every planetary target, yes it had taken longer to cold soak but there was soo much more detail seen on any decent night as in regards to seeing. The C9.25 at times would best the M703 on Saturn and Mars but on Jupiter it was a close one but always the C9.25 would be best in show. On Lunar the mac was always the best scope for jaw dropping views, it was always like the mac was made for lunar so unless you had a bad sample of a C9.25 then I have really issue with it not being a good scope on planets. 


 

#180 CHASLX200

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Posted 29 October 2018 - 07:21 PM

I had an excellent 10” Newt.  I now have a 9.25 Edge HD.  IMHO, the views are at least as sharp in the cat as they were in the Newt.  I would go so far as to claim that the views are even better in the cat.  

 

I also have a “standard” C8 that gives soft views.  Because of this I don’t use this scope for visual at all, but it is fine for EAA.

 

I’ve done side by side comparisons with the Edge, properly acclimated, and my Equinox 120 on planets - in particular Saturn on a night of fair to good seeing.  I would say that it was a wash.  Both scopes delivered very good views.

Depends on the Newt brute. I can't say how good your Newt was.  I do think the C9.25 would be the better choice out of all the SCT's for planets if i had to pick a SCT.


Edited by CHASLX200, 29 October 2018 - 07:21 PM.

 

#181 Jaimo!

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Posted 29 October 2018 - 08:03 PM

Going back around 2010 I had a very good sample of a C9.25, a Intes Micro M703 and before all those nice cats a Skywatcher 120ED. First off the 120ED was a nice scope for good all around planetary views but the M703 cleaned its clock on every planetary target, yes it had taken longer to cold soak but there was soo much more detail seen on any decent night as in regards to seeing. The C9.25 at times would best the M703 on Saturn and Mars but on Jupiter it was a close one but always the C9.25 would be best in show. On Lunar the mac was always the best scope for jaw dropping views, it was always like the mac was made for lunar so unless you had a bad sample of a C9.25 then I have really issue with it not being a good scope on planets. 

Skyjim, his scope was not collimated, I doubt he had a bad sample...  See here.  Occam's razor would agree.

 

Jaimo!


 

#182 Redbetter

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Posted 29 October 2018 - 11:27 PM

My new ES 127 Mak was no planetary scope either, until I collimated it.  My first two targets were a bright star and Jupiter.  Both looked poor so I immediately began trying to figure out how to collimate it.  The time it was putting up poor images was short, measured in hours only because there were no collimation instructions and the hidden collimation screws for this scope are a different arrangement than the Orion/Synta/Skywatcher Maks.  I did a rough collimation in poor seeing to get rid of substantial coma, then dialed in collimation a night or two later in decent seeing. 

 

"Conventional wisdom" is that Mak's don't need collimation... 4.gif    rofl2.gif   and that refractors don't need collimation either.  Odd, because I have had to center or collimate a few refractor doublets as well.  undecided.gif    SCT's are easier in that the manufacturers assume that collimation might require user adjustment, so they have them set up to do so, and with some instructions on what to adjust.  Compare that to some of the smaller Mak's (such as the ETX's) which are difficult to collimate, while some other Maks can be adjusted more easily but have no documentation on where the adjustment is or the sequence of screws to be turned.  Then there are the refractors that either have no built in adjustment or undocumented cells. 


 

#183 Boom

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Posted 30 October 2018 - 01:39 AM

There is an easy experiment to do that will put the "oh but digital processing can cover for optical defects" myth to bed:

Pick a night of good-to-excellent seeing, take an AVI of a planet. Deliberately miscollimate the scope till the image in the eyepiece is fuzzier. Take another AVI. Process both to the max and compare.

Any takers? Especially in the southern hemisphere where the ecliptic with the planets is high in the sky currently.

Tanveer

What is this supposed to prove?

Wouldn't it make more sense to process the miscollimated AVI to the Max and compare that to a not so heavily processed collimated AVI?

Edited by Boom, 30 October 2018 - 01:40 AM.

 

#184 DMach

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Posted 31 October 2018 - 11:07 AM

There is an easy experiment to do that will put the "oh but digital processing can cover for optical defects" myth to bed:

 

Pick a night of good-to-excellent seeing, take an AVI of a planet. Deliberately miscollimate the scope till the image in the eyepiece is fuzzier. Take another AVI. Process both to the max and compare.

 

Any takers? Especially in the southern hemisphere where the ecliptic with the planets is high in the sky currently. 

 

Tanveer

Been there, done that ... but not deliberately! 

 

As per my earlier post, I learned the hard way that even the "slightly defocused star" method was not accurate enough to extract the best performance from my SCT. With the help of the fantastic members on this forum, I learned about the high-power, in focus star test to precisely dial in collimation and have been using that ever since.

 

Disclaimer: these images are taken with a 6" SCT, not a 9.25" ... so don't take them as an indication of what the 9.25" can do.

 

Also not actually on the same night, but I live near the equator so I have the advantage of having the planets high in the sky all year 'round. Seeing is usually decent (3/5+) ... transparency is more often the issue, with so much moisture in the air.

 

With 'scope slightly miscollimated (notice in particular what appears to be "ghosting" of the planet limb, almost like image shudder):

 

Jupiter 2018-02-20.jpg   Jupiter 2018-03-24.jpg   

Saturn 2018-02-20.jpg

 

After dialling in collimation using a high-power star test:

Jupiter 2018-05-17 w Ganymede v1.jpg   Jupiter 2018-06-04 w Ganymede and Europa v6 25pc.png   

Saturn 2018-05-14 1.0x redux.jpg

 

 

What is this supposed to prove?

Wouldn't it make more sense to process the miscollimated AVI to the Max and compare that to a not so heavily processed collimated AVI?

I would agree with this statement: with good collimation and good seeing, less processing is needed in the first place. But there's only so far you can push any data set - processing can't recover inherently poor data or lack of detail, and over-processing becomes pretty obvious.

 

Another factor of course is getting focus spot-on when imaging ... took some practice for me!

 

And finally, for those trying to compare/equate "viewing" to "imaging" in the first place: I fully agree with prior posts that it's actually hard to get an image to compare to what my eyes can see through the eyepiece.

 

Important to remember that our eyes (and, more importantly, our brains) can do things that no telescope (or camera) can do:

  • Rapidly adjusting focus and providing a much larger apparent depth of field.
     
  • Dealing with high dynamic ranges of light intensity.
     
  • etc. etc.

 

Not to mention our brain's ability to "fill in the gaps" based on what is has learned to expect it should, as evidenced by countless optical illusions (such as this one).

 

So at the end of the day, you could in fact ask: is the image captured by an electronic sensor (even after processing) in fact more faithful/dependable than what you see with your eyes? wink.gif


 

#185 Tom Glenn

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Posted 31 October 2018 - 11:57 AM

Collimation is important, although the limb defect in the Jupiter images posted above has nothing to do with collimation, but is instead an artifact of stacking and processing.  Happens even with perfect optics and excellent seeing, and is constantly discussed on the imaging forum.  As far as collimation is concerned however, the importance cannot be overstated.  Often times, poor collimation is confused with bad seeing, or bad optics.  Rough collimation doesn't cut it with SCTs, and the performance impact is dramatic.  


 

#186 ensign

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Posted 31 October 2018 - 01:58 PM

Depends on the Newt brute. I can't say how good your Newt was.  I do think the C9.25 would be the better choice out of all the SCT's for planets if i had to pick a SCT.

And since my 9.25 compared favorably to a very good apo, you couldn’t go far wrong. Slightly dimmer and a bit more contrast with the refractor.  I counted one more of Saturn’s moons with the Equinox.


Edited by ensign, 31 October 2018 - 02:00 PM.

 

#187 Magnetic Field

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Posted 31 October 2018 - 02:10 PM

And since my 9.25 compared favorably to a very good apo, you couldn’t go far wrong. Slightly dimmer and a bit more contrast with the refractor.  I counted one more of Saturn’s moons with the Equinox.

 

The photos that people post here are really amazing.

 

One should let the refractor people in and show them what can be done with a comparatively (to refractors) cheap SCT.


 

#188 starman876

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Posted 31 October 2018 - 02:16 PM

interesting mix of opinions on which type of scope gave the best views.  I would say the only way to accurately determine if the SCT in question that started this post was a bad as the OP stated is that it  would need to be checked against a know good scope from the same location on the same night.   Their are so many variables that can account for poor images at the eyepiece.    Any speculation of what it might be might not be accurate unless all the conditions were known.  


 

#189 Foehammer

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Posted 31 October 2018 - 05:16 PM

I have been using C9,25's for planetary observing and imaging since 2009 and I can say this. If you pay attemtion to what the design needs to perform, then it will perform very well indeed!

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#190 wargrafix

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Posted 31 October 2018 - 05:27 PM

Collimation is not that hard
 

#191 Jaimo!

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Posted 31 October 2018 - 05:56 PM

The photos that people post here are really amazing.

 

One should let the refractor people in and show them what can be done with a comparatively (to refractors) cheap SCT.

Large SCTs are the preferred scope for planetary imaging, where a higher f/ ratio is desired.  Spend a little time on the Solar System Imaging forum, it is amazing the images you can attain from a relatively "inexpensive" scope (compared to APOs).  

 

Jaimo!


 

#192 Cpk133

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Posted 31 October 2018 - 08:10 PM

interesting mix of opinions on which type of scope gave the best views.  I would say the only way to accurately determine if the SCT in question that started this post was a bad as the OP stated is that it  would need to be checked against a know good scope from the same location on the same night.   Their are so many variables that can account for poor images at the eyepiece.    Any speculation of what it might be might not be accurate unless all the conditions were known.  

 

If the op still owns this scope, I'd be willing to meet up and a to b next summer when the planets are back and the weather / seeing is more hospitable.


 

#193 DMach

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Posted 01 November 2018 - 01:05 AM

Collimation is important, although the limb defect in the Jupiter images posted above has nothing to do with collimation, but is instead an artifact of stacking and processing.  Happens even with perfect optics and excellent seeing, and is constantly discussed on the imaging forum.  As far as collimation is concerned however, the importance cannot be overstated.  Often times, poor collimation is confused with bad seeing, or bad optics.  Rough collimation doesn't cut it with SCTs, and the performance impact is dramatic.  

Hi Tom, the Gibbs artefact was considered as part of the troubleshooting (see the link I posted) but the limb "ghosting" was also present in the raw frames. Ultimately, it was collimation that improved the situation. I do still get the Gibbs effect of course, but at more "normal" levels (as per the latter, "after collimation" images).

 

Quite possible that stacking and sharpening exacerbated the issues, of course!


 

#194 Tom Glenn

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Posted 01 November 2018 - 03:48 AM

Hi Tom, the Gibbs artefact was considered as part of the troubleshooting (see the link I posted) but the limb "ghosting" was also present in the raw frames. Ultimately, it was collimation that improved the situation. I do still get the Gibbs effect of course, but at more "normal" levels (as per the latter, "after collimation" images).

 

Quite possible that stacking and sharpening exacerbated the issues, of course!

Also, I think that to some degree, Jupiter (and Saturn) have some limb effects similar to the "rind" artifact observed on Mars, but to a much lesser degree.  Notably, with Mars, the artifact does not come from stacking or sharpening but rather from diffraction of light as it passes around Mars and through its atmosphere.  The artifact is definitely visible in the raw frames.  I have seen Jupiter data behave somewhat similarly, but the degree to which this happens is much less than Mars and seems to vary somewhat inconsistently night to night, probably dependent on seeing and some unknown variables.  Collimation could indirectly affect things by reducing detail in the image overall, and allowing the sharpening scheme to inappropriately exaggerate the limb defect.

 

Post #16 from your referenced post (by John Boudreau) basically states what I just did above regarding diffraction. 


Edited by Tom Glenn, 01 November 2018 - 03:53 AM.

 

#195 Bomber Bob

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Posted 01 November 2018 - 06:19 AM

I think that to some degree, Jupiter (and Saturn) have some limb effects similar to the "rind" artifact observed on Mars, but to a much lesser degree.

 

I've seen it, and I bet a lot of other planet imagers have, too -- and probably attributed it to their camera and/or techniques.  Thanks for pointing that out.


 

#196 Asbytec

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Posted 01 November 2018 - 08:32 AM

So, is the presence of the rind effect evidence we cannot process out diffraction and aberration effects? After processing, the real(?) image has not been deconvoluted by technology.
 

#197 BarrySimon615

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Posted 01 November 2018 - 01:08 PM

At the risk of being pedantic, I wrote "9.25 SCT," singular, and not "9.25 SCTs." I did not say nor did I imply they were all bad. I could have written "this" or "my," to reinforce that, but chose not to because is I had no reason to assume that mine is not a representative sample. And as a durable item in good working order, I expect companies to supply a good, working item the first time, even if it is 2nd hand. It's not my job to protect Celestron's reputation or the feelings of its management. Of course, I realize now it needs columation, which may or may not solve the problem. In any event, I will not apologize or retract my observation and this is the last I will comment on this matter.

Have you attempted to collimate your Celestron 9.25 yet?  It is likely that the poor images that you were seeing and reporting that led to the creation of this thread could be solved by good collimation.  I think we are all curious to know how your scope performs after it is in proper alignment.

 

Barry Simon


 

#198 Bean614

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Posted 01 November 2018 - 04:05 PM

"Have you attempted to collimate your Celestron 9.25 yet?".  

 

I agree with Barry's question, and am waiting to hear the answer myself.

 

But, the OP wrote "Of course, I realize now it needs columation, which may or may not solve the problem. In any event, I will not apologize or retract my observation and this is the last I will comment on this matter."

 

   Some SCT users just refuse to collimate their scopes, for whatever reason.  Fear?  Don't know how? Or, as the OP seems to say, they expect that, EVEN with a second hand scope, the manufacturer is responsible for keeping the scope in perfect collimation for the duration of it's life!  And this, when every SCT manufacturer lists in the owner's manual, direct instructions for collimating the scope.  It's usually in the section called Care & Maintenance.  It's like changing the oil in your car.  Is Honda responsible if my 6 year old CRV stops working well, or at all, if I haven't changed the oil since I bought it?


 

#199 Achernar

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Posted 01 November 2018 - 04:43 PM

Your experience matches mine.   

 

There was (is?) an urban legend that the C9.25 is somehow "special" but stacks of iterferometer tests testify that it is a scope that is rarely anything special optically.  The quality varies quite a bit, and the chances of getting a really good one seem to be about the same as getting a barely passable one.

 

Coupled with the large obstruction, you get a scope that is in my own experience, a very poor planetary instrument and near the top of my list of telescopes to avoid for that application.  I know the SCT crowd will hate me, but I have owned pretty much every SCT model made, and the C9.25 to me was simply the worst overall in terms of performance per inch of aperture.  The fact that a good 5" Achromat would equal or best a C9.25  on planets does not surprise me at all.

 

My top recommendation to people that want to do more serious planetary observing is a cheap 8" or 10" dob with a mirror that has been refigured to a high Strehl ratio.  This will be a hard scope to beat on planets even with a $10,000 Apo. 

 

Anyone that has had the chance to  view planets through a really finely made 8" or 10" premium mirror reflector on a night of even pretty good seeing will tell you that they offer extremely detailed planetary views and views that are far more colorful than high power views with smaller instruments like a 6" Apo (and yes, I have owned one of those too, and a very good Astro-Physics one at that). 

I had the opportunity to look at Mars and Saturn through my 10-inch F/4.5 Dob and a 6-inch F/9 Meade apochromatic refractor at magnifications as high as 400x during good seeing. The view through the APO was noticeably more contrasty than through the Dob, and the features on Mars were more apparent probably because it was an unobstructed telescope while mine was. Nevertheless, the views through the Dob were very good and did not give up much to the APO, but critical examination shows it had better contrast. As for my SCT, I have an 8-inch EdgeHD, and when the seeing is good and the telescope cooled down, I get very nice views of the planets and moon through it. I like the views through bigger Dobs even better, the best views I ever had of Jupiter and Saturn I ever had with my telescope was when I looked at them through my 15-inch during periods of excellent seeing.

 

Taras


 

#200 Ron359

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Posted 03 November 2018 - 10:44 PM

 

There was (is?) an urban legend that the C9.25 is somehow "special" but stacks of iterferometer tests testify that it is a scope that is rarely anything special optically.  

 

Where are these "stacks of interferometer tests" of 9.25" SCTs?  Please provide complete references or links.  


 


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