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Having a Hard time justifying getting a C-9.1/4

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#1 George Methvin

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Posted 18 January 2020 - 09:52 AM

Hi folk I have a C-8 and really enjoy it but I have for many years secretly wanted to get a C-9.1/4 but have not done so and one of the reason is the cost the ota they are not cheap. I have a nice old Meade LXD-75 mount just setting not around not being used and was wondering if a C-9.1/4 would ride on it ok,I am mostly a visual observer but also like to do some planetary photos some times but not very often. Now here's where I have a hard time justifying this I will turn 68 in a few months but I am in good shape so first would a C-9.1/4 show me that much more then my C-8 to make it worth while getting and would the C-9 be much more heavier  to haul in and out to set up? Would I be duplicating what I already have at the cost of  around a thousand dollar more or should I just stick with what I have,inquiry minds would like to know LOL. Thank you all for your input and clear skies.



#2 RaulTheRat

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Posted 18 January 2020 - 10:01 AM

I have been looking at these a bit and the original non edge 925 is quite big, almost like a C11 in size and weight. The flip side is that this is because it has a slower primary and is reputed to be better corrected than the rest of the line.

I think the edgehd are all the same primary focal ratio so the size and weight scales more as you would expect.

#3 Traveler

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Posted 18 January 2020 - 10:17 AM

Read what Ed Ting wrote about your question:

https://www.scoperev....com/CSCTs.html



#4 Eddgie

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Posted 18 January 2020 - 10:30 AM

Read what Ed Ting wrote about your question:

https://www.scoperev....com/CSCTs.html

I think Ed Tings review is responsible for the urban legend where people think that the C9.25 is somehow going to have better optics than the other SCT models.

 

I can point to a half a dozen interferometer tests that completely disprove that urban legend.  The quality of these varies, so if someone is thinking of buying one, they should not expect it to be any better than any other SCT and should buy it solely on whether its characteristics match their desires.


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#5 astro42

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Posted 18 January 2020 - 10:38 AM

Ok let's get back too the 8" over the 9 1/4 being justified cost/weight.

I don't think its enough of an upgrade in aperture that it will make a huge difference over the 8".


Edited by astro42, 18 January 2020 - 10:38 AM.

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#6 macdonjh

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Posted 18 January 2020 - 10:38 AM

George Methvin,

 

I look at it in terms of incremental gain.  When I needed to cure aperture fever I went from a 4" scope to a 6" scope.  Quite a revelation, but of course, it was approximately 100% gain in light gathering.  My next step was from 6" to 11" (a C11, coincidentally).  Again, a revelation, of course. 

 

I had that C11 for five years, and a 10" scope for a few years after that.  After making that jump I noticed I started thinking the view through an 8" scope looked dim, but a view through a C9.25 looked quite similar.  I sometimes wondered why I didn't get a C9.25 instead...

 

But, then, I reversed my point of view of the argument: if stepping back from the C11 to the C9.25 wouldn't be that big a change in my observing experience, then stepping up from a 6" to a C9.25 wouldn't have been as big an improvement, either.  The two thoughts don't quite follow each other, but I felt better just the same.

 

I don't think you'll notice that big an improvement going from a C8 to a C9.25 (C6 to a C9.25 or C8 to C11, sure).  If you're looking for a "light bucket" consider a 10" or 12" Dobsonian and put it on a furniture dolly so you can leave it assembled and wheel it to your observing spot.  The 12" especially will provide you with a huge gain in image brightness compared to your C8.  You can still use your C8 to dabble in planetary photography.



#7 Traveler

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Posted 18 January 2020 - 10:39 AM

I thought the maker of this C9.25 urban legend was Todd Gross? 



#8 macdonjh

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Posted 18 January 2020 - 10:40 AM

I think Ed Tings review is responsible for the urban legend where people think that the C9.25 is somehow going to have better optics than the other SCT models.

 

I can point to a half a dozen interferometer tests that completely disprove that urban legend.  The quality of these varies, so if someone is thinking of buying one, they should not expect it to be any better than any other SCT and should buy it solely on whether its characteristics match their desires.

But a 1/4-wave f/3 mirror must provide better images than a 1/4-wave f/2 mirror, right?  It works like that, doesn't it? smile.gif



#9 Eddgie

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Posted 18 January 2020 - 10:41 AM

Hi folk I have a C-8 and really enjoy it but I have for many years secretly wanted to get a C-9.1/4 but have not done so and one of the reason is the cost the ota they are not cheap. I have a nice old Meade LXD-75 mount just setting not around not being used and was wondering if a C-9.1/4 would ride on it ok,I am mostly a visual observer but also like to do some planetary photos some times but not very often. Now here's where I have a hard time justifying this I will turn 68 in a few months but I am in good shape so first would a C-9.1/4 show me that much more then my C-8 to make it worth while getting and would the C-9 be much more heavier  to haul in and out to set up? Would I be duplicating what I already have at the cost of  around a thousand dollar more or should I just stick with what I have,inquiry minds would like to know LOL. Thank you all for your input and clear skies

First, I have owned the C90, the C5, the C8 (well, three of them to be complete), the EdgeHD 8, the C11, and the C14.

 

First, vs the C8, I would say that the increase in performance is rather small.  Now bigger is better, but here, you move to a substantially bigger OTA for what I perceive as a rather small gain in all aspects of performance. 

 

The C8 will work comfortably on a lot of light weight mounts and depending on your mount, the C9.25 could push it over the edge. 

 

Remember, with the C9.25, it is not just the OTA weight, but also the added counterweight that is required to balance it and having owned  a C9.25 on an Meade LXD 55 and a Celestron ASGT5, I would say that while the C9.25 will work on it, you are pushing the capacity of the mount.  This limits you to the C9.25 though because the C11, which would be my own recommended upgrade from the C8, is too much for these mounts.

 

So, it is not just the weight of the OTA, it is the weight of the extra counterweight and now the extra effort required to haul all of the pieces out.

 

Now I can't tell you that it is or is not worth it, but I can tell you that the improvement is very small vs the effort you would expend. 

 

If you want more aperture my advice would be to grab a 10" dob.   This will give you a wider field than you can even get with your C8 and will give C11 levels of deep sky performance.  The OTA on these generally weighs in at just of 30 lbs, so a bit heavier than the C9.25, but about the same as a C9.25 and the counterweights you would need to balance it, and far less than the tripod, mount, counterweights, and C9.25 OTA.

 

So, yeah, you can get away with it on your mount, but it is pushing it and the actual increase in performance is (in my opinion) subtle.

 

I upgraded from an 8" SCT to a C9.25, and that lasted me about six months. I was never happy with it.  The optics were just so-so and the extra effort required was out of proportion to the performance increase. 


Edited by Eddgie, 18 January 2020 - 10:41 AM.

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#10 Eddgie

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Posted 18 January 2020 - 10:48 AM

I thought the maker of this C9.25 urban legend was Todd Gross? 

Well, both had something to do with it, but I first read the magic dust report on Ed Ting's website.  In my own experience, I found zero magic in the C9.25. It was perhaps the biggest disappointment I ever had in the SCT world, but I blame that on heightened expectations.  My own experience was the optics were so-so and the performance improvement over the C8 was just eh. 

 

Sadly, for the OP, his mount puts him in a box.  The C11 is an absolutely worthwhile upgrade, but not one that the LXD-75 is capable of dealing with (in my opinion). 

 

Again, a 10" dob would be a far more compelling upgrade.  Better everything. Wider fields, more contrast, brighter images, considerably better limiting magnitude, and frankly, easier to get out and observe with for many observers.  The C9.25"?  Not so much.  Just too little umph vs the C8.  Better? Sure.  Enough to offset the 30 lbs of extra hassle?  Only the OP can say.   But that is the point here.  His weight difference will go up almost as much as if he bought a 10" dob and when the entire weight differential and setup hassle is factored in, even a 10" Go2 dob is looking light. 


Edited by Eddgie, 18 January 2020 - 10:50 AM.

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#11 Bill Barlow

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Posted 18 January 2020 - 10:56 AM

He doesn’t want a Dob.  I wonder why people keep suggesting this when he wants to use the scope on his LX75 mount.  I don’t think you can mount a 10” Dob on this mount.

 

As far as upgrading from a C8 to a C9.25, there will be some gain in seeing deep sky objects with 34% more light gathering.  Since you have always wanted to try one and you’re not getting any younger, go for it!  Maybe you will really like it.  I don’t own that mount, so can’t comment if it will ride on it okay.

 

Bill


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#12 Eddgie

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Posted 18 January 2020 - 10:56 AM

But a 1/4-wave f/3 mirror must provide better images than a 1/4-wave f/2 mirror, right?  It works like that, doesn't it? smile.gif

Not really.   It has nothing to do with center of the field performance. If you made the C9.25 as a scaled up C8, it would have exactly the same performance as the f/3 mirror variant at the center of the field. The speed of the primary has zero relevance here.  The SA is corrected by the corrector, and you can make the mirror as fast as you want as long as you use the correct power on the secondary to correct the spherical aberration. 

 

The field in the C9.25 will be a tiny bit flatter, but the speed of the mirror itself makes no difference in terms of the performance at the center of the field.   In this case, it is simply not a factor. 



#13 Eddgie

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Posted 18 January 2020 - 11:00 AM

He doesn’t want a Dob. 

 

Bill

He did not say he didn't want a dob.. You said that.  

 

Again, he is in a box though because probably the biggest scope the LXD-55 can handle is the C9, but the difference in performance comes with the need to haul out a heavier scope and an additional counterweight.   It is a big price for a tiny gain in limiting magnitude and contrast transfer. 35% light gain sounds like a lot, but in reality, it is just a tiny fraction of a magnitude and a tiny improvement in image scale

 

 

you’re not getting any younger, go for it!

And yes... Exactly why I think it is time to evaluate where the OP wants to go.   If he ever wants a truly meaningful upgrade, he should do it now.   It only gets worse from here.  

 

I am 68 though, and even my 12" dob is easier to manage than my C9.25 on my Losmandy GM8 Mount was (I went to the GM-8 because I felt the Celestron ASGT was not sufficient, but in the end, the GM8 was not any  better for the C9.25 in terms of stability). 


Edited by Eddgie, 18 January 2020 - 11:07 AM.

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#14 petert913

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Posted 18 January 2020 - 11:09 AM

Thanks for this good input.  I was toying with the same conundrum as George.  Now I can just keep my C8 and be happy !


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#15 Eddgie

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Posted 18 January 2020 - 11:34 AM

And let's remember how telescopes work here.   For extended objects like Galaxies and Nebula, exit pupil sets the image brightness.  Any galaxy that he can see in the C9.25 is going to be visible in the C8.   For the same exit pupil, the scale will be 16% larger in the C9.25 but that is not that much really (assuming the same exit pupil).  Neither of these scopes is particularly good for galaxies though because they have a lot of transmission losses. 

 

I put the numbers into an on line calculator and dismissing transmission and shading losses, here is how the LM works out.

 

The 203mm scope will have limiting magnitude of   14.24  vs.14.56, so that is only 1/4 of a magnitude difference.  That is pretty small (though I think that these are optimistic except for extremely dark skies).

 

And hey, I have owned these.  The difference in performance (in my own opinion) is subtle. The difference in mount loading is considerable.  Not that the LXD-75 can't carry it, but it is a lot of load for the heavier scope and the extra 10 lb counterweight. 

 

The OP asked for opinions though, and having owned both scopes and a similar sized mount, I would say that there are better ways to spend one's money.   A quarter of a magnitude and 16% increase in image scale is balanced against 20 extra pounds of gear, a smaller true field, more corrector dew controller current, and $1000. 

 

If the goal though is to get the absolute most performance out of the existing mount, then the C9.25 is the only real option here. 


Edited by Eddgie, 18 January 2020 - 11:38 AM.

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#16 Jeff Lee

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Posted 18 January 2020 - 11:34 AM

Not to bring up the devil, buy a ZWO290 or 224 and using sharpcap you C8 becomes "bigger". @70 that is what I did (added the FR3.3 to use with the 224) and then added the 294MC. Am putting both the C8/ES102 on a JMI wheely bar (10" wheels) and my 20 year old C8 will outlive me and I'll see things from my B6 sky that only a 20" at a dark sky would show me. 8" SCT are the perfect EAA scope IMHO.



#17 George Methvin

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Posted 18 January 2020 - 11:38 AM

Yes thanks everyone I had kind of guess what the answers would be and so I think I will keep my C-8 and my money  the C-8 I have has to me very good optic and is easy to use and gives great views of the planets and star cluster short of a jack of all trades and a master of none so the saying goes . Once again thanks for the help.


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#18 Eddgie

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Posted 18 January 2020 - 11:46 AM

Yes thanks everyone I had kind of guess what the answers would be and so I think I will keep my C-8 and my money  the C-8 I have has to me very good optic and is easy to use and gives great views of the planets and star cluster short of a jack of all trades and a master of none so the saying goes . Once again thanks for the help.

You have nailed the essence of the C8 and the reason that is is one of the most popular telescopes ever made.  It is an awful lot of telescope for the size and weight and I think perfectly matched to the mount you have it on. 


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#19 Eddgie

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Posted 18 January 2020 - 11:47 AM

By the way, what part of Central Tx are you in if I may ask?



#20 George N

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Posted 18 January 2020 - 12:02 PM

Planetary imager Damian Peach has settled on the C9.25 -- see here for his reasons: http://www.damianpea.../c925review.htm


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#21 jgraham

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Posted 18 January 2020 - 12:27 PM

Just for yucks...

 

I have a couple of LXD75s including an LXD75 SC8 and a couple of C8s. I also have a set of 10" SCTs and a C11 that I use on an Atlas. I did a fair amount of planetary imaging with the LXD75 SC8 and with a bit of patience it did a grat job! The larger scopes are incrementally 'better', but the degree of more better is largely controlled by the seeing. I suspect that a C9.25 would be okay on an LXD75, but I would not want to put a 10" on it.

 

Sooooo, if someone has an itch that they gotta scratch I think that they'd do okay, but the improvement over an 8" would be incremental. Sometimes every little bit helps.

 

Enjoy!



#22 Cali

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Posted 18 January 2020 - 01:06 PM

Here's an argument for the C-9.1/4 with a teleconverter.

 

That's just about as close as your gonna get without commandeering a LEM.

 

- Cal 


Edited by Cali, 18 January 2020 - 01:24 PM.

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#23 PowerM3

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Posted 18 January 2020 - 01:10 PM

I have owned and used both side-by-side. I have also owned an LCD-75 as my grab and go mount for years. In my experience the 9.25" is nothing special and really not worth the upgrade from the c8. Its ether the c11 or go home. The LXD-75 is not up to the task of the c11 though. If you would like more info check out my comparison of the scopes on my blog:  http://www.avt-astro...-12-lx-200-racf



#24 Bataleon

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Posted 18 January 2020 - 01:44 PM

If you already have a C8 and want to go big, you're better off saving your pennies for the 11 imo. 925s aren't enough of an upgrade to justify the purchase in my mind, but that's just me. Only way I'd go that route is if I found a great deal on a used one.

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#25 jerobe

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Posted 18 January 2020 - 01:46 PM

Sometimes when I have an itch to buy something in this hobby that is "a bit more, better, bigger" than what I already have, and I wait a while, the itch just goes away...


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