9 replies to this topic

[tocster]

So I purchaed a carbon fibre C11 late last year to replace my Meade 12inch ACF which was just too much scope for me to manage.  Scope looked in excellent condition overall and it was a decent (not amazing, but decent) price and local.

 

When collimating I noticed that not only did the fastar holder for the secondary move around, it moved up and down and side to side.  thought that the holder must have come loose, I did eventually manage to remove the fastar ring, but there was no way to tighten the holder (even by shoving my hand in the opening) - so I then attempted to remove the corrector plate. 

 

I've done this on serveral other SCT's so it didnt daught me - but the first thing I noticed was that the metal retaining ring wouldnt easily come off - after some effort I noticed that it appeared to be gummed up with some residue - looked carefully and saw that the material (foam or rubber?) was pretty hard and degraded - it had left a lot of crud on the corrector.  It was also impossible to remove the plate - it was stuck on the other side by the same compressed foam/rubber.  I added some IPA around the corrector and after letting it soak for 10 minutes the corrector popped off.  Yay!  I played around with the secondary holder attempting to tighten it to no avail - then I added some more IPA around the inside of it, and eventually the holder did tighten up, and now there is no play or movement. 

 

So far so good - now the fun begins to clean the corrector.  After about an hour of failure (I would clean, and find new residue finding it way to the surface) I realised that the corrector edge was covered in some sort of white paint or glue - this was the culprit - I then used cotton buds and various solvents to remove the white stuff, and after some effort got the corrector cleaned nicely.

 

I guess to the topic title - is it normal to have foam/rubber on the place the corrector sits in the OTA and is it normal to have a white glue/paint on the edge of the corrector?  Both seem to have degraded.  I dont believe this scope is super old. (mid 2010's I think)

 

 

 

 

[choward94002]

Hmm .... nope, I believe that something was added aftermarket by someone ... I have several C11 and C14 OTA's from that era (or close to it) and those also had the floppy secondary but the corrector with those were floating on a lip on the plate cell carrier (the front thing) with small cork shims keeping the corrector lightly tight (and which those shims dried out and contracted the corrector also went floppy)

 

Sounds like you did the right thing, removing the junk and such ...

[RichA]

So I purchaed a carbon fibre C11 late last year to replace my Meade 12inch ACF which was just too much scope for me to manage.  Scope looked in excellent condition overall and it was a decent (not amazing, but decent) price and local.

 

When collimating I noticed that not only did the fastar holder for the secondary move around, it moved up and down and side to side.  thought that the holder must have come loose, I did eventually manage to remove the fastar ring, but there was no way to tighten the holder (even by shoving my hand in the opening) - so I then attempted to remove the corrector plate. 

 

I've done this on serveral other SCT's so it didnt daught me - but the first thing I noticed was that the metal retaining ring wouldnt easily come off - after some effort I noticed that it appeared to be gummed up with some residue - looked carefully and saw that the material (foam or rubber?) was pretty hard and degraded - it had left a lot of crud on the corrector.  It was also impossible to remove the plate - it was stuck on the other side by the same compressed foam/rubber.  I added some IPA around the corrector and after letting it soak for 10 minutes the corrector popped off.  Yay!  I played around with the secondary holder attempting to tighten it to no avail - then I added some more IPA around the inside of it, and eventually the holder did tighten up, and now there is no play or movement. 

 

So far so good - now the fun begins to clean the corrector.  After about an hour of failure (I would clean, and find new residue finding it way to the surface) I realised that the corrector edge was covered in some sort of white paint or glue - this was the culprit - I then used cotton buds and various solvents to remove the white stuff, and after some effort got the corrector cleaned nicely.

 

I guess to the topic title - is it normal to have foam/rubber on the place the corrector sits in the OTA and is it normal to have a white glue/paint on the edge of the corrector?  Both seem to have degraded.  I dont believe this scope is super old. (mid 2010's I think)

It  boggles the mind, but unsuitable material is often found in scientific instruments, particularly black foams and other material that deteriorates over time.  I've cleaned some unreal messes because of it.  I guess as long as it lasts during the warranty period...

[tocster]

I guess another question - given that the secondary moved around and is not in the position from the factory, is it possible to re-align it? will it affect image quality?  Im thinking yes. 

 

I had an idea of using a laser in the focus tube and tape some grease proof paper on the secondary opening to see if it shines in the centre.

[macdonjh]

It's been years since I disassembled the C11 I used to own, but I don't remember having any trouble removing the corrector.  That said, there are many posts here about observers with stuck corrector plates.  You followed the exact first recommendation: apply a few drops of alcohol, allow it to wick into the gap and soak, then gently pry the parts.  Repeat as necessary.

 

I believe there are often three or four spacers around the circumference of the secondary assembly, usually cork, but I think more modern Celestron scopes use some kind of polymer.  Again, there are lots of threads here about missing, or incorrectly placed spacers as well as recentering the secondary mirror (and the corrector plate itself).

 

Remember, the rotational orientation of the corrector plate matters.  There is supposed to be a black mark on the edge of the corrector plate (put there by the assembly technician at Celestron).  The mark should be oriented at 3:00 when you view the scope from the front.

[JeremySh]

I wonder if someone has used a polymerising Lens cleaner like this: https://www.comaropt...er-film-cleaner

and not cleaned the polymer off properly 

[whizbang]

No, it's not normal.  Somebody gummed it up.

 

In the olden days, Celestron marked the correctors at the 3 o'clock position.  I don't think newer scopes have marks.  My sense of the thing is that newer plates are manufactured more consistently.  So, the orientation of the corrector isn't critical like used to be.

[carolinaskies]

Uncle Rod mentioned in a 2020 post on his blog about this gasket material.  http://uncle-rods.bl...ot.com/2020/06/

[tocster]

Uncle Rod mentioned in a 2020 post on his blog about this gasket material.  http://uncle-rods.bl...ot.com/2020/06/

Thanks a lot, very interesting read.  There where no shims on my corrector, but it did have the engraving at the 3 oclock position.  Interestingly the front retaining ring has nothing on it as all, its just a plain black ring - looking at images on the internet that seemed to be a feature of the carbon fibre model?

 

WRT the gunk on the edge of the corrector - I've bought enough second hand gear to know that I have a special place in hell for people (who think they know more than they do) that 'mod' or 'improve' the manufacturers design and then on-sell their creations.  This scope has gone though a few owners and now I am left with something I feel uncomfortable selling off - I guess if I put it though its paces and it performs no harm done.

[luxo II]

Get rid of the stupid mods - restore it sensibly, and it should be fine.

 

My pet hates are scratched correctors, damaged screw heads, Bobs Knobs, garbage focusers and flocking. A scratched corrector cannot be fixed, but the rest can. And shims are easily replaced.

Edited by luxo II, 17 September 2023 - 03:58 AM.