27 replies to this topic

[Debacle]

Question that someone can hopefully help me answer. I have a Seestar S50 which was my first scope. I have since purchased a Spacecat51 and enjoy the wide views I get, but I also want something I can 'Zoom' in and get some detailed images. I see locally on marketplace there is a Celestron C9.25 OTA for sale, but it has a crack on the corrector plate. The seller mentions it doesent affect optical quality, but is this a big no and should I stay away? I have attached a picture of it.  

Attached Thumbnails

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Edited by Debacle, 13 June 2025 - 04:13 PM.

[Sheremy01]

I would stay away. If it’s cracked it’s liable to shatter into pieces.

[randcpoll]

You probably want to stay away. Not necessarily because of the crack, but because it will likely require a much bigger mount than you have.
If you already have a big mount then it comes down to the price. Cracks like that don't affect the image too badly if you are just going to use it for visual.

But if you ever want to resell it you're not going to get much out of it.

[siriusandthepup]

If you can get it for 200-300$, why not? Get it, use it, sell it for parts when you are tired of it (or the crack finishes it off).

 

 

 

cheap amusement. Also lets you try out a type of telescope that maybe you would not have ever gotten the chance to try.

 

gl

[TOMDEY]

It adds character and is a good conversation piece. I'd snap it up before someone else realizes its value.     Tom

[NDBirdman]

$200 I'd pick it up but much more.... run way.

[Brain&Force]

I'll concur with the others and suggest you stay away (unless it's being sold for cheap enough that you're willing to accept writing it off). The problem with cracks isn't that the crack itself will ruin the image - worst case, you can just black out that portion of the corrector. It's that the crack may have altered the internal strain of the glass and caused the precise figure of the corrector to be altered.

 

The figure of a Schmidt corrector barely deviates from a flat panel of glass, so it's not something you can evaluate from this picture or by just looking at it (unless it's perceptibly deviating from flat, in which case, the scope is a loss). Even looking through it in the daytime may not reveal issues unless it's a serious change in figure - stars are the ultimate test of optical quality. If you really want to go for it, test it at night.

 

Rule of thumb: a chip, scratch, gunshot, or other local imperfection makes little difference to the image, and in the worst cases it can be blacked out. A small deviation across the whole surface renders an optical element unusable.

 

And I will also agree with randcpoll in that you'll need to invest in a beefy, quality mount to image with a scope of this size.

[Bob4BVM]

I'll concur with the others and suggest you stay away (unless it's being sold for cheap enough that you're willing to accept writing it off). The problem with cracks isn't that the crack itself will ruin the image - worst case, you can just black out that portion of the corrector. It's that the crack may have altered the internal strain of the glass and caused the precise figure of the corrector to be altered.

 

The figure of a Schmidt corrector barely deviates from a flat panel of glass, so it's not something you can evaluate from this picture or by just looking at it (unless it's perceptibly deviating from flat, in which case, the scope is a loss). Even looking through it in the daytime may not reveal issues unless it's a serious change in figure - stars are the ultimate test of optical quality. If you really want to go for it, test it at night.

 

Rule of thumb: a chip, scratch, gunshot, or other local imperfection makes little difference to the image, and in the worst cases it can be blacked out. A small deviation across the whole surface renders an optical element unusable.

 

And I will also agree with randcpoll in that you'll need to invest in a beefy, quality mount to image with a scope of this size.

Had to laugh at your wild generalization on the gunshot statement.

We're not talking a 100" mirror here. 

Any kind of gunshot to a C9.25 would destroy all of the optics in this scope

Edited by Bob4BVM, 13 June 2025 - 05:07 PM.

[Debacle]

Thanks guys. What I was figuring with the crack as well. Guy wants $600 for it. Currently have an AVX mount which I know is too small to handle it, but I was more looking at it as a starting point.

[Keith Rivich]

Thanks guys. What I was figuring with the crack as well. Guy wants $600 for it. Currently have an AVX mount which I know is too small to handle it, but I was more looking at it as a starting point.

I would offer $100 and see if he bites. 

[WadeH237]

I doubt that the crack affects performance much at all.

 

I'd be more wary about using it for deep sky imaging, unless you have a very good mount and lots of experience.  It's not the size or weight of the scope; it's the focal length (even with a reducer).

 

Imaging with an SCT is a whole different ballgame from imaging with a RedCat 51.  My suggestion, if you want to capture some finer details, would be to look for a refractor in the 800mm to 1000mm range.  My main imaging scope is a 5" refractor at F/6.3.  It was an upgrade over the 8"  EdgeHD that I used to use as my main imaging scope.

[vtornado]

Unless you are going for high resolution imaging (planets/lunar) I would not choose this scope.   I see these for sale for around $1000.00 with a good corrector.  $600.00 is too much.  Are you going to want to use the fastar with a cracked corrector?

[dnrmilspec]

First, an AVX is OK to use with a 9.25" Scope for visual.  I have one set up like that in my garage right now.  Celestron sells them as a set.  Astrophotography is another thing altogether.

 

I am in the $100.00 or less group.  For the $600.00 he is asking you could get a very nice 8" OTA and it would ride beautifully on your AVX.  There is a difference between the 9.25 and the 8" but it is subtle to say the least.  Given what you have now an 8"  would be a great addition.  

 

That crack makes the scope virtually worthless.  I have a 6" that is virtually new with a broken corrector and I would be thrilled to get anything for it.  I advertised for a new corrector for it and got not a single response.  And I called Celestron.  A new corrector would cost virtually as much as a new OTA.  I say this to illustrate that someday that corrector is going to completely fail.  If it doesn't take out your mirror in the process, the cost of replacing it will make yours just a major frustration.

 

In addition to a used 8" SCT with the $600.00 you could get an Explore Scientific 8" Dob complete from Astronomics.  You could get a new 5" Mak that would be a rock and planet killer on your AVX.  You could get a used 6" Achromat which is a totally fun scope.  In other words, for $600.00 there are far better choices than a broken 9.25" scope.  

[maniack]

First, an AVX is OK to use with a 9.25" Scope for visual.  I have one set up like that in my garage right now.  Celestron sells them as a set.  Astrophotography is another thing altogether.

 

I am in the $100.00 or less group.  For the $600.00 he is asking you could get a very nice 8" OTA and it would ride beautifully on your AVX.  There is a difference between the 9.25 and the 8" but it is subtle to say the least.  Given what you have now an 8"  would be a great addition.  

 

That crack makes the scope virtually worthless.  I have a 6" that is virtually new with a broken corrector and I would be thrilled to get anything for it.  I advertised for a new corrector for it and got not a single response.  And I called Celestron.  A new corrector would cost virtually as much as a new OTA.  I say this to illustrate that someday that corrector is going to completely fail.  If it doesn't take out your mirror in the process, the cost of replacing it will make yours just a major frustration.

 

In addition to a used 8" SCT with the $600.00 you could get an Explore Scientific 8" Dob complete from Astronomics.  You could get a new 5" Mak that would be a rock and planet killer on your AVX.  You could get a used 6" Achromat which is a totally fun scope.  In other words, for $600.00 there are far better choices than a broken 9.25" scope.  

What little I know of astrophotography tells me that a scope with such a long focal length such as the C9.25 is a pain in the neck to use for a beginner. A very robust mount and quite accurate guiding are necessary here. Obviously with a cracked corrector using a Hyperstar is out of the question, and even on a good scope is not close to beginner-friendly.

 

A far better starter high-magnification scope would be a C5 (or equivalent such as the 5SE), which can be had in very good condition for less than $400. The focal length with 0.63 corrector/reducer installed is just under 800mm. Or a C6 isn't a bad choice either.

[Dave Mitsky]

I do not recommend buying that C9.25.

[Inkie]

I would give it a pass, although I might change my mind if I understood, and felt okay about, the cause of the crack.  Was it from impact, and where was the impact?  Did the force of the impact possibly cause other problems, such as mechanically stressing or 'tweaking' the primary mounting and causing a lot of mirror flop when focusing or when tracking across an apex of an arc?  Was it simply due to too much torque on one screw retaining the retainer ring?

[Jon Isaacs]

I do not recommend buying that C9.25.

 

 

Unlike Dave, I recommend not buying it.   

 

Cracks propagate.. Obviously $600 is way out of line.  

 

Jon

[Don W]

RUN AWAY!!

[bunyon]

Yeah, it might be fine right  now. It's doubtful it stays fine. For $100, sure. And visually, it'd be great on the AVX.

 

For $600? No way. Tough break (ha! I crack (I did it again!) myself up) for the seller. 

[johnsoda]

Actually, if it’s a diametral crack, and it looks like it might be, it may not propagate further.  It’s essentially reached an edge on both ends (well, I’m assuming it has - you can’t be sure without removing the secondary ring and the outside corrector-plate ring), and those edges are constrained.  However, I still wouldn’t buy it unless it was extremely cheap.

[NinePlanets]

I'd pay $100 for it, easy.

But not $600

[PKDfan]

I'd go to ~200$ myself.

Its been determined that optical quality even with more severe issues & with even worse cracks is quite neglible if doing AP.

Thats a linear full length crack that probably wont propagate further.

Yup it deserves a closer consideration and could be a very wise choice for so few dollars.

Heck if it was closer to me i'd jump on it.


CSS
Lance

[maniack]

Heck if it was closer to me i'd jump on it.

But the asking price is $600, which is outrageous for the condition.

[PKDfan]

But the asking price is $600, which is outrageous for the condition.

I'd have three 50dollar bills in plain view maniack and if a No then i'd add one more and if still a no then i'd simply laugh and walk away.

When the seller realizes their mistake when person after person offers no where near that amount then the sun may suddenly come out and personal wisdom may be attained.

Asking 600$ is utterly insane.


CSS
Lance
Edited typos

Edited by PKDfan, 14 June 2025 - 06:33 PM.

[vtornado]

I might let the seller stew a month or so then offer $200.  I still don't think I would hang a camera off the fastar.

 

If the scope was dropped it may be off of colimation, and tightening the screws on  a cracked corrector ... (na na na moe, larry ...)

Edited by vtornado, 14 June 2025 - 06:34 PM.