Opinions please re C9.25 corrector plate marks

[PeterCPC]

I have noticed that my Celestron C9.25 has some "smears" on the inside of the corrector plate. It doesn't look like fungus and I have always had a plug with silica gel in the end to prevent moisture.

I have attached photos. My quandary is whether to do anything about it. I really don't want to remove the corrector plate to clean it.

What's your opinion? Will this affect any imaging?

Thanks

Peter

[Alkaid]

Does look a bit smeary, definitely on the inside?  (Silly question, as I know you will have double checked).

I'd be hesitant to remove the corrector myself unless I'd had prior experience, you'll probably know that the orientation of the plate matters immensely when re-assembling.  Plus always the worry of dropping it etc.

It might be good to have it professionally cleaned.

 

[PeterCPC]

Definitely on the inside.

Peter

[Peter Drew]

A rather odd appearance, looks like residue from a previous clean.  SCT correctors, over time, tend to get "milky" due to outgassing of the factory internally applied paint but this is usually more uniform over the complete surface.  I doubt whether it would have a significant impact on imaging, something to consider if selling in the future.   🙂

[PeterCPC]

It's never had an internal clean - bought from new. I am considering taking the corrector out to clean but I am a bit hesitant.

Peter

[Greymouser]

I have a C 9.25 too and no way would I consider doing that myself. It would be down the road the Crewe and Orion Optics to have it professionally seen to!

[inapottingshed]

22 minutes ago, PeterCPC said:

It's never had an internal clean - bought from new. I am considering taking the corrector out to clean but I am a bit hesitant.

Peter

Not sure I'd attempt it either but there is a video on YouTube of someone cleaning a C14 corrector plate. 

[billhinge]

Mine was similar but it cleaned off eventually

[PeterCPC]

12 hours ago, billhinge said:

Mine was similar but it cleaned off eventually

How did you find the process? Was it easy? Any tips welcomed.

Peter

[billhinge]

Its easy to open up and remove the plate. There is a plastic retainer with some cardboard shims and the glass sits on  a  circular ledge. After removing the retainer just mark the edge of the glass and tube so you can put everything back in the right orientation. Make sure you use the correct size screwdriver to avoid tearing the screw heads

You may read on cloudynights that there are celestron marks and serial numbers already on the glass, well my circa 2010 model didn't  have any

From the outside you may think it is wafer thin glass but its actually quite hefty

There are loads of videos and methods on the internet, I tried using water alcohol and acetone to clean it in the past (you can see I flocked the tube some years ago). 

I use those microfibre cleaning cloths and paper tissue for dabbing off liquid (one of those pc blowers helps remove dust etc)

Don't spray liquid on the glass but apply it to the cloth and clean small areas a bit at a  time. Alcohol products seem to leave a slight purple residue or smear so I actually found distilled water and detergent the best. Applied water to the cleaning cloth and residue  gently wiped away, dry with a second cloth and blower.  In all plan for a weekend, its not a  rush  job, just needs patience. Acetone can work on small stubborn spots but I think you could get away with water if you take longer

Check and double check before you screw everything back together, it may look clean and shiny in your hands but any marks really stand out when you have a black tube and mirror as a backdrop

Putting the shims back under the plastic and then trying to find the screw holes is a nightmare as the shims will move respective to the plastic ring. Easier to add glue to to the ring & cardboard shims to keep  them lined up before trying to replace, glued together its a simple job.

After you put everything back  you  need to collimate everything - still need to do  mine, I have one of the Hotech laser jobbies, done it before just  haven't got around to it yet

So the out take is it requires patience and methodical working

[PeterCPC]

Thanks. That certainly sounds achievable so I will be having a go in the near future.

Peter

[PeterCPC]

I did it today. Good tip about the shims.

It looks good but you can get obsessive about every little mark if you are not careful. Shining a bright light in shows some very minor marks but without the light it looks good. Now to collimate - if we ever get a clear night.

Many thanks @billhinge for the suggestions. If you are considering cleaning yours - give it a go.

Peter

[billhinge]

thank you and good  luck collimating 🙂

 

[PeterCPC]

I adjusted the collimation screws indoors to get it about right and then did a star test last night. It was spot on and needed no further adjustments.

For anyone else who might find this helpful. I put the scope on the mount and adjust it so that I can look directly down the OTA from about 1.5m away - I then adjust the collimation knobs until all the circles that you can see in the tube are completely concentric. Takes a bit of patience but it obviously works.

Peter

[Mr Spock]

41 minutes ago, PeterCPC said:

For anyone else who might find this helpful. I put the scope on the mount and adjust it so that I can look directly down the OTA from about 1.5m away - I then adjust the collimation knobs until all the circles that you can see in the tube are completely concentric. Takes a bit of patience but it obviously works.

Exactly what I do! Then on to a star test, and Bob's Knobs make that a doddle compared to fiddling with a screwdriver in the dark.

[PeterCPC]

1 minute ago, Mr Spock said:

Exactly what I do! Then on to a star test, and Bob's Knobs make that a doddle compared to fiddling with a screwdriver in the dark.

Yep. Bob's knobs all the way.

Peter

[jonathan]

On 05/09/2020 at 11:06, billhinge said:

Putting the shims back under the plastic and then trying to find the screw holes is a nightmare as the shims will move respective to the plastic ring. Easier to add glue to to the ring & cardboard shims to keep  them lined up before trying to replace, glued together its a simple job.

Just been through this with my 8SE, I found the card gaskets / shims easy to put back - just hold them in place with one screw then the rest is easy.

[Starwatcher2001]

I like the idea of marking the collimation knobs with a white blob so you can see how far you've turned them. 🙂

[billhinge]

On 13/09/2020 at 08:20, Mr Spock said:

Exactly what I do! Then on to a star test, and Bob's Knobs make that a doddle compared to fiddling with a screwdriver in the dark.

I find it fiddly, how do you easily get your arm into the big  C11 dewshield while adjusting Bob's Knobs, the dewshield  always gets in the way.

If you take the dewshield off then wont the corrector dew  up.

Am I missing some obvious trick here?

[Mr Spock]

My corrector never dews up even without the dewshield.

[billhinge]

Unfortunately mine does if  left unheated, I'm pretty close to the sea so prone to humidity, ah well I was hoping you had a magic solution

I find you need the arms of an octopus to  look through the eyepiece and turn the knobs

Edited September 14, 2020 by billhinge

[Starwatcher2001]

On the odd occasion my scope needs collimating, I leave it outside for a good hour with the cover on the front, then remove the cover and collimate it, then put the dew shield on, then use as normal. However, I'm around 9 miles inland and it sounds like you have a much more extreme problem with dew. Is it practical to put the heater on without the dew shield, and would that help? 

Maybe set up the scope underneath a tree, car-port or other overhang. That might stave off dew formation for a while longer.

[billhinge]

I had planned to insulate my  C11 to keep the heat in, anecdotal evidence does seem to indicate that works. Plus last time I  did this I was using a high power eyepiece on a CG5 mount wearing several layers of clothing which didn't help. 

I've upgraded my mount since then plus I'm mullti-camera  and fully computer equipped which may help

(I have the full hotech laser collimator so I can get it ballpark before )

[Dustspeakers]

On 05/09/2020 at 11:06, billhinge said:

Its easy to open up and remove the plate. There is a plastic retainer with some cardboard shims and the glass sits on  a  circular ledge. After removing the retainer just mark the edge of the glass and tube so you can put everything back in the right orientation. Make sure you use the correct size screwdriver to avoid tearing the screw heads

You may read on cloudynights that there are celestron marks and serial numbers already on the glass, well my circa 2010 model didn't  have any

From the outside you may think it is wafer thin glass but its actually quite hefty

There are loads of videos and methods on the internet, I tried using water alcohol and acetone to clean it in the past (you can see I flocked the tube some years ago). 

I use those microfibre cleaning cloths and paper tissue for dabbing off liquid (one of those pc blowers helps remove dust etc)

Don't spray liquid on the glass but apply it to the cloth and clean small areas a bit at a  time. Alcohol products seem to leave a slight purple residue or smear so I actually found distilled water and detergent the best. Applied water to the cleaning cloth and residue  gently wiped away, dry with a second cloth and blower.  In all plan for a weekend, its not a  rush  job, just needs patience. Acetone can work on small stubborn spots but I think you could get away with water if you take longer

Check and double check before you screw everything back together, it may look clean and shiny in your hands but any marks really stand out when you have a black tube and mirror as a backdrop

Putting the shims back under the plastic and then trying to find the screw holes is a nightmare as the shims will move respective to the plastic ring. Easier to add glue to to the ring & cardboard shims to keep  them lined up before trying to replace, glued together its a simple job.

After you put everything back  you  need to collimate everything - still need to do  mine, I have one of the Hotech laser jobbies, done it before just  haven't got around to it yet

So the out take is it requires patience and methodical working

I've only just seen this thread. I had almost exactly the same kind of staining on my C925 which I put down to condensation inside the tube and storing the OTA with corrector plate down, i.e. on the scope cap, so that the condensed water ended up resting on the inside of the corrector plate. Unfortunately, due the the looooong intervals between imaging sessions in UK, I didn't notice the this for a while and was horrified to see a stain on the inside of the glass.

So I was also faced with the dilemma of what to do, and after watching the Internet videos I decided to clean it myself. There were a couple of issues. Firstly, I couldn't remove the corrector plate without removing one of the scope cap retaining pins, and secondly the stain was so ingrained that in order to remove the stain, it also removed a small section of the coating on the inside of the glass. Other than that, the job went pretty much as described in the quoted section. It doesn't _seem_ to have affected the optical quality much on the basis of images taken since. Given the above, in what orientation do you store your OTAs. I've looked for recommendations on t'Interweb but can't see anything.

[PeterCPC]

I store mine horizontally.

Peter