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Equipment Discussions >> Cats & Casses

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jerry10137
sage
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Reged: 01/26/13

Loc: Texas, USA
What makes the C9.25 so special? new
      #5699839 - 02/25/13 01:19 PM

Curious minds want to know. The reason I ask is because the used ones literally get scooped up really fast.....almost instantly

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MikeBOKC
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Reged: 05/10/10

Loc: Oklahoma City, OK
Re: What makes the C9.25 so special? new [Re: jerry10137]
      #5699842 - 02/25/13 01:21 PM

I suspect it is because they are an excellent sweet spot in aperture, portabiity and versatility for either visual or AP, or both. They will ride comfortably on EQ mounts like the CG-5, or larger if one wants more stability. Kind of a Goldilocks SCT, not too big, not too small, just right.

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dweller25
Pooh-Bah


Reged: 08/30/07

Loc: Lancashire, UK
Re: What makes the C9.25 so special? new [Re: jerry10137]
      #5699844 - 02/25/13 01:22 PM

I think this is mostly hype - which I fell for - my C9.25 was nice but nothing "special".

My FS128 on the other hand ..........


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wolfman_4_ever
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Reged: 07/15/11

Loc: El Segundo, Ca, So. Cal
Re: What makes the C9.25 so special? new [Re: dweller25]
      #5699852 - 02/25/13 01:29 PM

lol!



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Dave Venne
member
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Reged: 11/12/07

Loc: Burnsville, MN, USA
Re: What makes the C9.25 so special? new [Re: wolfman_4_ever]
      #5699866 - 02/25/13 01:37 PM

Good question, because I fell for the mystique--not that I regret getting one in the least. I like the size, it is a sort of sweet spot thing for me. The 9.25 is about the biggest SCT I can handle without worrying about damaging it or myself. At f/10 its field is nice and flat for imaging, and the scope works well on my CGEM. I like it, but is it special? Don't know. Give me some other SCTs for comparison and I'll get back to you. Eventually.

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MrJones
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Reged: 09/15/10

Loc: Indiana
Re: What makes the C9.25 so special? new [Re: Dave Venne]
      #5699936 - 02/25/13 02:23 PM

This old topic? As per some posts above what makes it special for me is that it's the biggest GOTO aperture that is easy to manage and will go on the lightweight mounts. I keep mine fully assembled in the garage on the LXD75 with counterweights even and it's easy to pick it up and carry to the driveway or backyard.

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jerry10137
sage
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Reged: 01/26/13

Loc: Texas, USA
Re: What makes the C9.25 so special? new [Re: MrJones]
      #5699943 - 02/25/13 02:30 PM

Sorry guys, I'm not trying to stir a pot here. I've seen several of them for sale in the last few months and they just get scooped up fast. I purchased one myself but only in that size because I knew it would be a happy medium for me. I'm going to upgrade and was curious if I should stay at 9.25 or go 11 in HD of course. I'm very anxious to look thru a 9.25HD

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vahe
professor emeritus


Reged: 08/27/05

Loc: Houston, Texas
Re: What makes the C9.25 so special? new [Re: jerry10137]
      #5699948 - 02/25/13 02:31 PM

If you look at the high end Maks you will notice that they all come with +/-F/3 primaries, for a given aperture their tubes are obviously much longer than SCTs.

SCTs use F2 primaries, a major compromise in the interest of compactness, there is one exception and that is C9.25, not F/3 but midway.

In theory F/2 or F/3 should not make any difference, in practice it is the opposite.

Vahe


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Eigen
member


Reged: 07/26/12

Re: What makes the C9.25 so special? new [Re: MrJones]
      #5699953 - 02/25/13 02:34 PM

I've read quite a few theories on the 9.25's mirror configuration being slower than that of other SCTs (F2 vs. F2.5-3.0) contributing to a less crucial critical collimation.

While I am unsure as to whether the above holds, I am quite sure in the fact that "most" SCT's out there are never critically collimated. I base this on countless SCT's at star-parties that I have had a chance to look through.

As most of you on here will know critical collimation is pretty tight on an SCT and the difference in the percieved optical quality changes quite dramatically when it is achieved.

What I am trying to say is that if the first statement holds, the likely factor contributing to the reputation of ethereal optical quality of the 9.25 series could simply stem from the fact that more folks got them properly collimated and compared them to less than perfectly collimated standard SCT's.

Just a theory though.


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orion61

*****

Reged: 10/20/07

Loc: Birthplace James T Kirk
Re: What makes the C9.25 so special? new [Re: Eigen]
      #5699970 - 02/25/13 02:47 PM

I think it was the fact for both the 9.25 and 6" were a totally new size for Celestron in some time, adding that to
the new computer control system that was guaranteeing very good optics in all Celestron scopes (and Meade) they hit the floor running and gained a reputation of bullet proof optics.
Both the 6 and 9.25 are very user friendly sizes.


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bob midiri
Carpal Tunnel
*****

Reged: 06/17/04

Loc: pa 19320
Re: What makes the C9.25 so special? new [Re: jerry10137]
      #5700017 - 02/25/13 03:11 PM Attachment (32 downloads)

Quote:

Curious minds want to know. The reason I ask is because the used ones literally get scooped up really fast.....almost instantly



I don't know some say hype, some swear by them. I own a C14 orange, and a Orange Super C8 both with in my mind exceptional optics. I also own an Ultima 9.25 with the digital focuser. If I was forced to keep just one it would be the Ultima....very refractor like images and quite portable. One nine volt battery runs it for hours. This one is something special, optically, mechanically....but I don't why it just is. Bob


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crsrs
super member
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Reged: 12/12/09

Loc: San Tan Valley, AZ
Re: What makes the C9.25 so special? new [Re: bob midiri]
      #5700295 - 02/25/13 05:43 PM

My Celestron Nexstar 9.25 GPS gives exceptional views and things like cool down times are quicker. The view is just beautiful. I like it better than any other scope I had.

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GeneT
Ely Kid
*****

Reged: 11/07/08

Loc: South Texas
Re: What makes the C9.25 so special? new [Re: MikeBOKC]
      #5700376 - 02/25/13 06:33 PM

Quote:

I suspect it is because they are an excellent sweet spot in aperture, portabiity and versatility for either visual or AP, or both. They will ride comfortably on EQ mounts like the CG-5, or larger if one wants more stability. Kind of a Goldilocks SCT, not too big, not too small, just right.




Well said.


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jerry10137
sage
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Reged: 01/26/13

Loc: Texas, USA
Re: What makes the C9.25 so special? new [Re: GeneT]
      #5700795 - 02/25/13 11:29 PM

Can you get a good clear focus with a quality 10mm eyepiece?

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bob midiri
Carpal Tunnel
*****

Reged: 06/17/04

Loc: pa 19320
Re: What makes the C9.25 so special? new [Re: jerry10137]
      #5701034 - 02/26/13 05:44 AM

When the atmosphere is steady i like using my 9mm Nagler, so yes. But that is with my particular scope

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freestar8n
Post Laureate
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Reged: 10/12/07

Re: What makes the C9.25 so special? new [Re: jerry10137]
      #5701083 - 02/26/13 07:23 AM

The regular C9.25 is definitely special because, as mentioned above, the primary is f/2.5 (I think) instead of f/2 - making the tube noticeably longer. Although this theoretically would have no impact on the on-axis performance for planets, it would have a big effect on flattening the field and reducing aberrations across a largeish detector.

But for the EdgeHD version, the field correction is taken care of by additional correction lenses - so the benefit of the slower primary would be greatly reduced. The overall field may still benefit from it, though, but all the Edge designs should be well corrected across the image - when collimated anyway.

Frank


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Eddgie
Postmaster
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Reged: 02/01/06

Re: What makes the C9.25 so special? new [Re: vahe]
      #5701197 - 02/26/13 09:03 AM

Quote:

In theory F/2 or F/3 should not make any difference, in practice it is the opposite.




Correct me if I am wrong, but wouldn't the f/3 help flatten the field as compared to the f/2 configuration?

It was my understanding that the C9 was slighly compromised toward imaging where the larger secondary obstruction would provide a bit better off axis illumination and the flatter field would give a bit better off axis sharpness.


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Eddgie
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Reged: 02/01/06

Re: What makes the C9.25 so special? new [Re: jerry10137]
      #5701226 - 02/26/13 09:20 AM

Quote:

Curious minds want to know. The reason I ask is because the used ones literally get scooped up really fast.....almost instantly





This is just an opinion, like so many CN responses, so take it for what it is worth.

And for what it is worth, I have owned C5s, C8s, C9, C11, and C14.

I believe that this is an urban legand that started with a web review site put up by Ed Ting about 12 or 13 years ago.

In the site, Ed Ting reviewed the C9. I don't know what other SCTs Ed Ting had in depth experince with prior to the C9 test, but Ed praised the C9 as the "SCT for people who don't like SCTs" or some such accolade.

He praised the scope for having good contrast. Of course if his only experience was with C8s, that would be true because when you move up in aperture with SCTs, the contrast natrually improves (contrast transfer improves with aperture all else being equal).

Along the way, somehow the rumor evolved to say that the C9.25 optics got special treatment.

This is another urban myth because the bench testing I have seen on C9.25s (Rohr in Germany has tested three I think) seem to show the same generaly variations in quality that many other Celestron scopes have shown over the years, (some good, some very good, some excellent... I personally think the C8 enjoys the most consistent optical quality in the Celestron lineup).

I don't choose to debate the merits of the C9. I owned one and found it to be nothing special in any way and more or less between the C8 and C11 in performance.

I do attribute the myth to Ed Ting's review though, and the "Optics are treated special" myth (which Rorh's testing shows is completely unfounded) as just an outgrowth of that.

We don't really know though if people still buy these becasue they think they are "Special" in any particular way.

Perhaps they are just popular because of the balance of size, weight, and aperture. That is why the C8s are so popular and why a lot of people stay with the C11 rather than move to a C14.

We can only speculate.

And of course my answer is only speculation, but having been on CN and the other forum for 15 years or so, I correlate the popularity to the publishing of Ed Tings review.

Heck, I bought one after reading his review. I was disappointed though and quickly sold it to repalce it with a C11.

Edited by Eddgie (02/26/13 10:25 AM)


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freestar8n
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Reged: 10/12/07

Re: What makes the C9.25 so special? new [Re: Eddgie]
      #5701236 - 02/26/13 09:26 AM

See my note just before yours.

I believe the primary is f/2.3 - according to some web sources. f/3 would make the tube a lot longer. But f/2.3 is a big change from f/2 since f/2 is so fast.

I don't think the secondary size is much bigger - they are all around 32-36%.

They could have flattened the field by keeping the primary f/2 and used a much larger and closer secondary - with a correspondingly lower overall f/number. But making the primary slower and the tube longer, while keeping the f/ratio the same, means they can flatten the field without increasing the secondary much. The downside is that the tube is longer. That's not so bad in the 9.25 size - but for C14 it would get pretty big, and a big attraction of the sct is that it is compact.

I guess the choice dates back to film days and they targeted this size specifically for long exposure 35mm work. So they knew they needed a flatter field. Now with CCD's and better guiding - they need a *really* flat field - but now provided by additional corrective lenses.

Frank


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Eddgie
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Reged: 02/01/06

Re: What makes the C9.25 so special? [Re: freestar8n]
      #5701334 - 02/26/13 10:22 AM

Ok, apologies for the mistake. My main point was that the design was a bit different most likely to slightly enhance imaging performance.

And I agree, there are a dozen different ways to configure an "SCT."

The "SCT" we buy is only one of several possible configurations, but being a commercial product, the designers clearly looked for the perfect middle ground in terms of design compromise, and I think they nailed it.

The optical compromises were fine when the designs were originated (Naglers didn't exist either when hypered Pan was being used), but I agree that they fell behind the times.

This is why I have said in the past (and still believe) that the EdgeHD design has made the standard SCT obsolete.

But your point is correct. The book Telescope Optics shows for different basic configurations for SCTs, but all of them make a compromise in either packaging or obstruction size.

You can't get too far away from the standard forumla without taking a hit in these other areas.

Edited by Eddgie (02/26/13 10:26 AM)


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