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9.25 SCT, it ain't no planet scope

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#226 Asbytec

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Posted 06 November 2018 - 10:43 AM

So, have we settled the question?
 

#227 Magnetic Field

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Posted 06 November 2018 - 12:02 PM

So, have we settled the question?

 

1. I think everyone is expecting the outcome and observing report after the telescope has been collimated.

 

2. I for one would like to know if things have improved after a successfull colimation session.

 

3. If things are still bad it can only mean there are other problems, e.g. spherical aberration and what else?


 

#228 Redbetter

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Posted 06 November 2018 - 01:46 PM

1. I think everyone is expecting the outcome and observing report after the telescope has been collimated.

 

2. I for one would like to know if things have improved after a successfull colimation session.

 

3. If things are still bad it can only mean there are other problems, e.g. spherical aberration and what else?

 

It is going to be difficult to get any sort of reference for the planetary comparison for some time.  Mars is in the 11 arc second range now and shrinking rapidly.  I don't know about NE Ohio, but this time of year usually brings poorer seeing to the places I have lived.   Jupiter won't be back in view for some months and will be much lower than before, about the declination that Saturn has been. 


 

#229 Deep13

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Posted 06 November 2018 - 04:14 PM

1. I think everyone is expecting the outcome and observing report after the telescope has been collimated.

2. I for one would like to know if things have improved after a successfull colimation session.

3. If things are still bad it can only mean there are other problems, e.g. spherical aberration and what else?


I will let everyone know, but it may not be until spring. The weather around here is usually overcast from Nov. through April at least. Plus, during the academic year, I have very little time for such things.
 

#230 Deep13

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Posted 06 November 2018 - 04:16 PM

It is going to be difficult to get any sort of reference for the planetary comparison for some time. Mars is in the 11 arc second range now and shrinking rapidly. I don't know about NE Ohio, but this time of year usually brings poorer seeing to the places I have lived. Jupiter won't be back in view for some months and will be much lower than before, about the declination that Saturn has been.


Yeah, that too, no planets for a while.
 

#231 Magnetic Field

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Posted 06 November 2018 - 04:52 PM

I will let everyone know, but it may not be until spring. The weather around here is usually overcast from Nov. through April at least. Plus, during the academic year, I have very little time for such things.

The moon may be an object (e.g craterlets in plato).

 

If your scope wasn't sharp on planets it wasn't good at observing the moon either.

 

You should also see some improvement when observing the moon.


 

#232 Bomber Bob

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Posted 06 November 2018 - 08:53 PM

CATs are complicated.  I own or have owned a variety of these designs.  To get the most from one, you have to collimate it.  Assuming it was made well, and the optics are clean & collimated, it will give fine views of the planets when the seeing cooperates.  I've seen it myself.  When my Vixen VMC200L is "close enough" with a quick laser check, I get small stars, but with very short comet tails.  When I collimate on a star at 200x, this 8" Field Maksutov acts like a Big APO, but weighs less than my Edmund 4" F15 refractor.

 

I used to think that CATs :: refractors was a +2 / +3 relationship.  An 8" SCT = a 6" refractor; or, a 6" MAK = a 4" frac.  Like these scopes, it's more complicated than that.  On some objects my dinky Questar is like a 6" Newtonian.  It just depends.

 

I've only looked through one Celestron Edge 9.25, but its lunar & planetary performance was excellent.  I don't know what aperture refractor I'd compare it to, and I really don't care.  

 

I'm in it for the views, doesn't matter to me what scope makes them.


 

#233 Tom Glenn

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Posted 06 November 2018 - 08:56 PM

The moon may be an object (e.g craterlets in plato).

 

If your scope wasn't sharp on planets it wasn't good at observing the moon either.

 

You should also see some improvement when observing the moon.

100% true.  Resolving fine structure on the Moon is optically the same challenge as for planets, and is severely impacted by collimation.  But it can be tricky to assess what is "good" or not on the Moon if one does not have a lot of experience looking at it, and a frame of reference for what kinds of detail should be expected with different scopes under good conditions.  


 

#234 highfnum

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Posted 06 November 2018 - 09:05 PM

I did this lunar with c925 I did pick up  rille feature or at least parts of it 

fc2_save_2018-09-30-062207-0000c925.jpg


 

#235 Bomber Bob

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Posted 06 November 2018 - 09:17 PM

Visually, my Edmund 4" F15 can show the rille and some of the small craters along the floor.  But I doubt I could replicate those views with my ASI120.


Edited by Bomber Bob, 06 November 2018 - 09:18 PM.

 

#236 Tom Glenn

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Posted 06 November 2018 - 11:01 PM

I took this with my C9.25 Edge HD.  As far as the optics are concerned, I have nothing but good things to say about this scope.  It has performed extremely well on the Moon and planets.  (You will have to click image for full size).

 

Plato_Vallis_Alpes_TG.jpg


Edited by Tom Glenn, 06 November 2018 - 11:05 PM.

 

#237 Asbytec

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Posted 06 November 2018 - 11:18 PM

100% true.  Resolving fine structure on the Moon is optically the same challenge as for planets, and is severely impacted by collimation.  But it can be tricky to assess what is "good" or not on the Moon if one does not have a lot of experience looking at it, and a frame of reference for what kinds of detail should be expected with different scopes under good conditions.  

Yes, it is in terms of being an extended object. I think the difference may be in the scale and level of contrast. The moon tends to have very high contrast features like Plato's craterlets (even though the floor of the crater itself is somewhat dark.) This allows us to resolve higher contrast features to smaller scales. Planets, with Jupiter being a benchmark, have lower contrast features. On these scales, the obstruction does limit resolution a bit, more similar - in my view - to a close unequal double which can prove difficult with an obstruction. 


 

#238 Tom Glenn

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Posted 07 November 2018 - 12:21 AM

Yes, it is in terms of being an extended object. I think the difference may be in the scale and level of contrast. The moon tends to have very high contrast features like Plato's craterlets (even though the floor of the crater itself is somewhat dark.) This allows us to resolve higher contrast features to smaller scales. Planets, with Jupiter being a benchmark, have lower contrast features. On these scales, the obstruction does limit resolution a bit, more similar - in my view - to a close unequal double which can prove difficult with an obstruction. 

True, but the obstruction only reduces contrast transfer in the low frequency zone of the MTF curve (such as Jupiter cloud belts) relative to scopes of approximately equal aperture. But I was only referring to using the Moon as a benchmark for the quality of the optics and the accuracy of the collimation, since Jupiter is long gone for awhile.  And unfortunately, north of the equator Jupiter is so low (and soon to be lower) in the sky that it will be difficult to really test the optics.  I was able to get a few images of Jupiter this season, but I don' know if I ever completely tapped the potential of my C9.25 Edge because of the low altitude.  

 

Jup_222942_TG.jpg

 

Jupiter_June27_223700_TG.jpg


 

#239 Deep13

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Posted 07 November 2018 - 03:10 AM

100% true.  Resolving fine structure on the Moon is optically the same challenge as for planets, and is severely impacted by collimation.  But it can be tricky to assess what is "good" or not on the Moon if one does not have a lot of experience looking at it, and a frame of reference for what kinds of detail should be expected with different scopes under good conditions.  

Impacted? Is that a crater joke?lol.gif


 

#240 Asbytec

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Posted 07 November 2018 - 04:16 AM

True, but the obstruction only reduces contrast transfer in the low frequency zone of the MTF curve (such as Jupiter cloud belts) relative to scopes of approximately equal aperture. But I was only referring to using the Moon as a benchmark for the quality of the optics and the accuracy of the collimation, since Jupiter is long gone for awhile.  And unfortunately, north of the equator Jupiter is so low (and soon to be lower) in the sky that it will be difficult to really test the optics.  I was able to get a few images of Jupiter this season, but I don' know if I ever completely tapped the potential of my C9.25 Edge because of the low altitude.  

 

attachicon.gif Jup_222942_TG.jpg

 

attachicon.gif Jupiter_June27_223700_TG.jpg

Tom, I do not disagree. Having observed some very small craters on Plato's floor with an obstructed 6" scope, maybe we both know how important really excellent seeing is to even approach the (high contrast) resolution limits of a modest (or any?) aperture. So, yes, if evaluating contrast (optics) can be done on such small scales less than Dawes (for comparison, not applicability). But, seeing has to be spectacular. On Jove, the offending first ring and a bit more, where aberration and obstruction do the most damage, is a little further out in angular diameter. A bit beyond the Airy disc and first ring. That damage is done near 0.6 and 0.7 spatial frequency. I believe the belts and larger contrast features on the order of several arc seconds are much lower spatial frequencies on the left side of the MTF. In this realm, both obstructed and unobstructed begin to normalize fairly rapidly. Most of the damage is done on the right hand side of the graph. 

 

You're images are absolutely incredible. WOW. If you have a scope that visually shows half (sic) of that, sheesh be happy.  That's a planetary scope. :)


Edited by Asbytec, 07 November 2018 - 04:19 AM.

 

#241 aa6ww

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Posted 07 November 2018 - 04:58 AM

Ive looked through many C9.25's and think its the best size SCT on the market for size vs performance. I've had many nights watching incredible Jupiter lunar and GRS transits. There was never a difference on planetary performance on an Edge vs a non edge, they are all excellent when set up correctly.

 

With an SCT, the collimation is just one part of how it performs. It also has to be well acclimated to the night skies, and most of all, the seeing conditions have to be excellent for it to perform at its peek.

 

There's no such thing as a true grab and go SCT because of the above mentioned factors.

 

...Ralph


 

#242 highfnum

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Posted 07 November 2018 - 06:37 AM

BomberBob ASI120 camera i assume?


 

#243 starman876

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Posted 07 November 2018 - 08:59 AM

anytime you have a folded light path you need to make sure everything is aligned properly.   It only takes a slight hair off and it will turn soft. The above images show what a good scope a C9.25 is.    Would be nice if there was a software program that would work with a CCD imager that  you could hook up a SCT that would allow us to dial in an SCT so the alignment was perfect.


 

#244 Axunator

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Posted 07 November 2018 - 09:26 AM

Would be nice if there was a software program that would work with a CCD imager that you could hook up a SCT that would allow us to dial in an SCT so the alignment was perfect.


Metaguide (freeware) and CCDInspector (rather expensive)?

Edited by Axunator, 07 November 2018 - 09:29 AM.

 

#245 Sarkikos

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Posted 07 November 2018 - 10:04 AM

In my experience, the best planetary scopes are moderately-sized Dobs.  My 10" f/4.8 has given me the most detailed planetary views of any telescope I've ever owned or ever looked through.  Aperture is important.  Aperture done well is more important.

 

By the way, I'm talking about visual observing, not imaging.  Those are two entirely different things.  I have no interest in pictures.  They do not give a good indication of what can be seen with the eyes, even of a skillful observer.

 

Mike


Edited by Sarkikos, 07 November 2018 - 10:09 AM.

 

#246 SandyHouTex

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Posted 07 November 2018 - 10:14 AM

I took this with my C9.25 Edge HD.  As far as the optics are concerned, I have nothing but good things to say about this scope.  It has performed extremely well on the Moon and planets.  (You will have to click image for full size).

 

attachicon.gif Plato_Vallis_Alpes_TG.jpg

I count 9 craterlets in Plato.  That is outstanding performance.


 

#247 Asbytec

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Posted 07 November 2018 - 10:44 AM

I count 9 craterlets in Plato. That is outstanding performance.


I count upwards of 20 in craterform. I'd like to get measurements from the smallest discernible craterform and see how well his scope is resolving. My smallest crater seen visually was miles diameter = 5.3/D inches.

Edited by Asbytec, 07 November 2018 - 10:48 AM.

 

#248 Bomber Bob

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Posted 07 November 2018 - 11:00 AM

BomberBob ASI120 camera i assume?

Yes, ASI120MC.  I started out with a used Orion StarShoot 2, and I could definitely say that I saw more than that camera imaged -- but for $35... not too shabby!

 

I try to keep the imaging requirements in mind, and only use the 120 when the seeing is 8 or better.  But that's tough when a year has been as lousy as 2018 -- I want to look more than shoot!

 

There's no such thing as a true grab and go SCT because of the above mentioned factors.

 

Yes, I have to Plan on using a CAT, and give it plenty of time to adapt.  Most nights at The Swamp, that means letting the scope warm up going from indoors to outdoors.  Our temp changes during most sessions are gradual, which does help.


 

#249 Sarkikos

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Posted 07 November 2018 - 11:29 AM

I think the 9.25 SCT could be a good planet scope for visual, but you do have to work at it.  It's not the kind of scope you can just plunk down in the back yard and start seeing fine detail on Jupiter or Mars.  (Is there really such a scope?)  Collimation and acclimation is what it needs. 

 

I don't care about what a photo shows or doesn't show.  I can download astro pics all day from the internet.  What can you see with your eyes at the telescope?

 

Mike


Edited by Sarkikos, 07 November 2018 - 11:33 AM.

 

#250 Ron359

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Posted 07 November 2018 - 12:01 PM

I think the 9.25 SCT could be a good planet scope for visual, but you do have to work at it.  It's not the kind of scope you can just plunk down in the back yard and start seeing fine detail on Jupiter or Mars.  (Is there really such a scope?)  Collimation and acclimation is what it needs. 

 

I don't care about what a photo shows or doesn't show.  I can download astro pics all day from the internet.  What can you see with your eyes at the telescope?

 

Mike

And what I care about is how much more detail I can get with imaging.  My location generally has poor to bad seeing, so I will never 'see' visually what I can get with 'lucky imaging'.  Not only do you need collimation and acclimation, but if you don't have excellent seeing when you "plunk it down,"  you will never get the views of detail on Mars and Jupiter you expect. If you're ignorant of these factors you will call it a 'bad scope, as some have claimed here.  So round and round this thread goes, with so much subjective preference with no point or conclusion possible.  

 

Yes, you can download images all you want, some of us prefer to try and make them and hope you like them.  And seeing is still by far the biggest limitation to producing good images, cause imagers already know that collimation and acclimation is critical but under your control.  It still amazes me how few of these 'naysayers' seem to follow any of the imaging and images posted every day, day after day on the planetary imaging forum.  

 

As professional astronomers have known for over a hundred years, images and data are the only objective form of making critical observations and discoveries or determining quality of an instrument in astronomy.  They gave up doing visual in the early 20th century.  Of course that shouldn't take away your preferred enjoyment of looking through a telescope, but its not going to settle any question of quality.  


Edited by Ron359, 07 November 2018 - 12:08 PM.

 


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