Cracked c9.25 corrector plate.

[Westmoorland]

After hearing many alleged scope pundits repeat how you should not be timid about cleaning both sides of a corrector plate and general disassembly, I thought I'd have a look at mine as practice for when my cleaning fluid arrives. I unscrewed 6 screws from the retaining ring, took it off then blew an electric air duster gently over both sides of the plate. I screwed it back in then and as everything seemed fine I put the dust cap back on. After 10 minutes I went to check the ring screws were tight enough... only to discover a hideous crack had developed, turning my scope into a piece of junk. I bought it second hand in August so no warranty. 

It's been a few hours since I discovered it and I'm pretty sure I can't live with it. I don't know why it has cracked as I only tightened the screws just enough to keep the ring firmly in place. If anybody has knowledge in this area that could take the sting out of this development it would be a relief, but if these plates cannot be replaced inexpensively I'm not using it or any telescope again. I'm not being melodramatic-- this incident really is that disgusting.

[Gfamily]

Oh no, how disappointing.

I don't know whether there are any UK companies that can offer a replacement service.  A quick google suggests that Grover Optics offer a replacement for the Celestron 8" SCT, and as the UK agent for Celestron, they may be able to help with yours. 

[Westmoorland]

10 minutes ago, Gfamily said:

Oh no, how disappointing.

I don't know whether there are any UK companies that can offer a replacement service.  A quick google suggests that Grover Optics offer a replacement for the Celestron 8" SCT, and as the UK agent for Celestron, they may be able to help with yours. 

I emailed Grover Optics to inquire. Thanks.

[Stu]

Sorry to see that, must be hugely disappointing. No idea why it happened, but perhaps there was a pre-existing stress somewhere that suddenly let go. Did you tighten the secondary holder at all, it looks like it started there.

@Peter Drew may be able to advise. I think correctors used to be matched with primaries but as I understand that’s not the case now.

[Peter Drew]

Unfortunate but maybe not as bad as it looks.  The optical power of the corrector is quite weak, just enough to balance the aberration of the primary mirror, as long as it is intact it may still function properly, give it a try.  The retaining ring screws should be turned until they stop, no further pressure.  If the telescope still works ok you might want to black out the crack.  Check the tightness of the retaining ring and back it off if necessary, if too tight it might propagate the crack further.

[Westmoorland]

20 minutes ago, Peter Drew said:

Unfortunate but maybe not as bad as it looks.  The optical power of the corrector is quite weak, just enough to balance the aberration of the primary mirror, as long as it is intact it may still function properly, give it a try.  The retaining ring screws should be turned until they stop, no further pressure.  If the telescope still works ok you might want to black out the crack.  Check the tightness of the retaining ring and back it off if necessary, if too tight it might propagate the crack further.

I'm pretty sure there was no excessive turning of the retaining ring screws. I did remove the secondary from the plate though I'm not sure that was necessary. I know technically it's not broken but I can't look at a cracked plate. Just mind these scope-pundits on youtube. My fault. Should have left it.

[JeremyS]

Really sorry to hear this. Makes me queasy just looking at the pic

[ollypenrice]

On the other hand, consider the various incarnations of front-camera imaging variants of this scope. They all have whacking great cables routed in front of the corrector. And look at that big secondary mirror in the light path. Try it before you panic.

Olly

 

 

[Highburymark]

Grovers sells replacement correctors for your scope - at £199 not cheap but for less than £200 you’ll have a new scope.

[Elp]

Different tensile force at play but this looks fairly strong:

https://m.youtube.com/watch?v=ool3pnpmAt4

 

[Westmoorland]

10 hours ago, Highburymark said:

Grovers sells replacement correctors for your scope - at £199 not cheap but for less than £200 you’ll have a new scope.

I hope your estimate is accurate. I was prepared for a figure like that, just about. On the other hand my local dealer--the Widescreen Center--say they emailed Celestron themselves for me, and they're waiting for an estimate and time slot. So, I feel slightly better.  

[Westmoorland]

10 hours ago, Elp said:

Different tensile force at play but this looks fairly strong:

https://m.youtube.com/watch?v=ool3pnpmAt4

 

That video is irresponsible if just one person gains the impression that a tight screwdriver turn will in no way cause a crack in his or her corrector plate. It my case, I'm pretty sure it did; though I can't rule out pre-existing stresses.

[Westmoorland]

11 hours ago, JeremyS said:

Really sorry to hear this. Makes me queasy just looking at the pic

That Ed Ting youtuber said if you hang around scopes often enough it's just a matter of when, not if, something gets dropped or breaks. I scoffed at his words but now just hope I've got the worst of  possible accidents out of the way.

11 hours ago, JeremyS said:

Really sorry to hear this. Makes me queasy just looking at the pic

11 hours ago, JeremyS said:

 

 

[SpaceWatcher]

I wonder if something like this would help mask and reinforce the crack

https://joytidy.com/products/2022-new-glass-repair-fluid?sku=18054560919003177861790523&gclid=EAIaIQobChMIm5T3wpfa-gIVi5ntCh07ggh2EAQYBiABEgIljPD_BwE

[Highburymark]

4 hours ago, Westmoorland said:

I hope your estimate is accurate. I was prepared for a figure like that, just about. On the other hand my local dealer--the Widescreen Center--say they emailed Celestron themselves for me, and they're waiting for an estimate and time slot. So, I feel slightly better.  

It’s on their website at £199 and suggests they are in stock

[Westmoorland]

7 minutes ago, Highburymark said:

It’s on their website at £199 and suggests they are in stock

They asked if I could travel to Teeside in their return email. I can't really. 

[Elp]

6 hours ago, Westmoorland said:

That video is irresponsible if just one person gains the impression that a tight screwdriver turn will in no way cause a crack in his or her corrector plate. It my case, I'm pretty sure it did; though I can't rule out pre-existing stresses.

The video is more for how much load the plate can take for people looking at RASA or Hyperstar purposes, it states that in the description. As per Olly's comment above the scope may work alright as it is.

From what I've read on adjusting corrector plates you screw in until you feel a small bit of resistance, no more. I'm surprised that yours has cracked though, it's one of the reasons I refuse to adjust mine.

I've read Toscan Optics (In Italy) can supply replacement corrector plates, Orion Optics (UK) can collimate, maybe they can also source the plates. But before you do this test the scope out, it may be okay.

Edited October 12, 2022 by Elp

[Louis D]

You've simply reinforced my conviction to only use Maks for travel scopes at 6" and under if the only other choice is an SCT.  Their thick meniscus correctors are practically invulnerable to damage in comparison to an SCT's thin corrector plate.

[allworlds]

That's painful, but remember scopes are for looking through not looking at. There's that one professional telescope with half a dozen black circles on its main mirror - bullet holes.

Louis D, you say that, but ENS Optical is selling a 6 inch Mak with a whacking great chip in its corrector. (Selling it very cheap, of course.)

[davidc135]

23 hours ago, Highburymark said:

Grovers sells replacement correctors for your scope - at £199 not cheap but for less than £200 you’ll have a new scope.

That would be an excellent price.  

This problem crops up regularly and often the solution consists of returning the scope to Celestron and paying for a new set of optics at considerable cost. If they are willing to supply only a replacement corrector that would be a great improvment for the customer.

There would be some value if you hang on to the cracked plate. Not huge but some. Grovers would bin it.

David

[Westmoorland]

9 hours ago, allworlds said:

That's painful, but remember scopes are for looking through not looking at. There's that one professional telescope with half a dozen black circles on its main mirror - bullet holes.

Louis D, you say that, but ENS Optical is selling a 6 inch Mak with a whacking great chip in its corrector. (Selling it very cheap, of course.)

Since the crack I notice a bizarre swirling pattern across the whole plate when I look at it from certain angles in the light. I'll take it outside again and see how it is. 

[VNA]

Hello, so sorry, to my understanding those corrector plates are unique to your scope?
It cracked possibly because it was repositioned incorrectly, there are marks on the side to match with the marks on the tube.

Have you looked through it if the image is "livable?" Wishing I had better news. :- (

[davidc135]

It's likely that the crack will make little difference to the views. I'd clean everything away from around the crack and compare views before and after blocking any transmitted light with a fine black sharpie. There'd be some extra diffraction effects. The reflected swirling effect is odd.

I expect corrector plates to be interchangeable and for the optics not to be matched but I could be wrong. Interesting question as is whether it would make any difference if the plate is rotated to an optimum position. It might do. Did Grovers make any comment on these questions?

David

[zernikepolynomial]

I am not sure what you did to the corrector plate around the crack. It looks like residue marks from something you put on it (maybe more cleaner?). Regardless, I think you should put some super glue right or glass adhesive onto the end of the crack (small amount), and if it sinks into the crack a bit, it might help it from getting bigger. Next, you should collimate it and see if the crack has permanently deformed the entire corrector, if it has, replace it. If its just causing a small amount of obstruction, then the scope will be fine because obstructions in the plane of the aperture (at the corrector and primary) become buried in the PSF (point spread function) due to the fourier effect of telescopes and lenses, and it will only reduce the contrast slightly. 

[RT65CB-SWL]

On 12/10/2022 at 15:38, Louis D said:

You've simply reinforced my conviction to only use Maks for travel scopes at 6" and under if the only other choice is an SCT.  Their thick meniscus correctors are practically invulnerable to damage in comparison to an SCT's thin corrector plate.

+1… my ETX105 survived a fall of 30-36” inches. The only thing that was damaged was two of the three mounting points and a crack of the ABS plastic housing on the rear end at the rear port which became next to useless with any ETX to SCT adapter and accessories attached. It now looks like this…

And the thing that saved the rest of the the OTA from any serious damage was that it fell on 2” of grass/lawn.

Edited October 13, 2022 by Philip R