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Need advice, should I clean my SCT corrector plate?


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Hi all,

I'm after a bit of help. I've been using my Celestron C8 SGT XLT for 3.5 years now and I live in a very damp area of the UK so over the years I've used it in some truly horrendous conditions and the fight with dew is constant and grinding (I use a dew shield and low settings on a hair dryer). Recently my images have been well below par and I'm really starting to wonder if my scope should be serviced/cleaned in some way. So I thought I'd post a few pics here in the hope that some of you guys could give me your opinion on whether or not I should attempt some kind of maintenance program on it (exact nature of which still to be decided).

Before anyone says it, I know well that the best advice for cleaning a corrector plate is... 'don't clean a corrector plate'.... but I know this scope well and the results I've been getting recently are really worrying (its well collimated)

As you can see from the pics, in addition to a lot of glued/dewed on dust there are some hideous damp splodges on the primary mirror as well. The first shot shows the whole corrector with a flash, to highlight the dust and the second without a flash to show it more realistically. The third is an extreme close-up (its like this all over) and the fourth shows the splodges on the primary, these are about 2-4mm in diameter and there's about 5 of them in total on the mirror.

Any advice/opinions gratefully received.

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I would certainly clean the corrector based on your photos. A layer of dust and grot will attract dew more readily. I would ignore the primary mirror for now, the benefit of cleaning is outweighed by

Hi Guys, I keep my scope in the shed - which is nearly at the outside temp - not sure if you want to bring a cold SCT into a warmer environment, as this would only create even more temp imbalance, cre

Hi, I've just had a quick read and the coatings seem to not be over coated for protection so be very careful - might be worth you holding off a little - wait to see if anyone has cleaned an SCT mirror

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It's really tough to know why your recent images are below par, and if the dust etc on your optics are the reason, or perhaps part of the reason.

As you've mentioned, the advice is usually to leave optics as they are........because it takes a great deal of grot on optics to make a noticeable difference.

How about showing some of your earlier and your later images for comparison, maybe the imagers on here may offer advise ?

Hope you sort it, Ed.

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I would give the corrector a clean, the coatings are resistant and as long as you're careful, you won't damage it.

I used Baader fluid and cotton wool balls and it came up like new.

Can't say about the mirror though.

You may want to consider a dessicant cap to stop any residual moisture affecting the primary.

Edited by Space Dragon
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Saw a post a while ago on CN forum, I think, with detailed instructions on dismantling  a Celestron SCT  cleaning and reassembling it.

Might be worth a search.

Dave

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Saw a post a while ago on CN forum, I think, with detailed instructions on dismantling  a Celestron SCT  cleaning and reassembling it.

Might be worth a search.

Dave

Link here http://downloads.celestron.com/Archives/Miscellaneous/Demounting-Optics.pdf

But I'd treat that as a last resort. If you do dismantle, please go carefully, and do an in depth search for more advice.

Hope you sort it, Ed.

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The mirrors should be clean without those blobs (fungus?) If it's there it should be cleaned so it won't spread more. Baader clean wonder and other alcohol/ether based solvents should do the trick. The corrector may need some cleaning with distilled water and those alcohol liquids (they may not dissolve some stuff from the plate, while water could).

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I would certainly clean the corrector based on your photos. A layer of dust and grot will attract dew more readily. I would ignore the primary mirror for now, the benefit of cleaning is outweighed by the potential risks. It might also be worth checking the diagonal, my 16" SCT was below par recently and I was horrified to see the state of its mirror. I will be cleaning the corrector shortly and usually use distilled water with a dash of washing up liquid and cotton wool balls. I point the OTA downwards to avoid the ingress of liquid, rinse off with distilled water, dry with a hairdryer and then buff up with dry cotton wool balls.. :smiley: 

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I wouldn't use Baader Wonder Fluid on the primary - best advice on that is the distilled water method, but as stated only as a last resort.  As for the corrector I have cleaned mine a couple of times and used the Baader Fluid with their micro-fiber cloth - works a treat and if you are careful should cause no damage.

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Thanks so much guys, really appreciate the advice. I don't know really what to do about the primary as I daren't attempt to dismantle the thing to get at it. I think I may need to content myself with cleaning the corrector, collimating it again and drying the whole OTA out thoroughly with desiccant gel packs before using it again.. and hoping for the best. Couple of spots on the mirror can't affect it that much right?…..  :(

so is this the correct wonder fluid?: http://www.amazon.co.uk/Baader-Optical-Wonder-Cleaning-Fluid/dp/B001ILNDOA/ref=sr_1_1?ie=UTF8&qid=1388652147&sr=8-1&keywords=baader+fluid

as for the micro fibre cloth this is the closest I could find on amazon? will this work?: http://www.amazon.co.uk/Microfibre-Cloths-Large-Cleaning-Kitchens/dp/B00AF6YWVC/ref=sr_1_fkmr0_3?ie=UTF8&qid=1388652933&sr=8-3-fkmr0&keywords=baader+micro+fibre+cloth

I've heard tales of de-ionised water mixed with alcohol, strained through coffee filters with windex added and a newts tail and bats eyes and stuff.. but that all seems a bit beyond my skill set so I'm happy to try the wonder fluid.

One more question, with regards to using the wonder fluid, could someone recommend an application method? i.e should I dab it on?, wipe it down? etc.. I do know not to apply the fluid direct to the plate and use it by applying it to the cloth first but not sure exactly how to go about the actual cleaning. 

Many thanks again :)

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I think you should spray it on and leave it to work. Dissolving is a non aggressive process. 

When, after a while, it's time to wipe the corrector there are two critical things. Never make a second wipe with whatever you just used. It is gritty after the first wipe. Always use a fresh wiping material. Secondly, never wipe in straight lines, always use curves. In the extremely unlikely event of a scratch the result will be far less visible through the optics.

There's nothing fancy about the recommended cleaning brews. Distilled water mixed with isopropyl alchohol availabe at a chemist plus one tiny droplet of washing up liquid. Nothing to it.

While the 'Don't clean it' advice is good there really is nothing to it when it comes to corrector plates, assuming you follow the advice. The coatings ae very hard. Mirrors, though, are coated with soft aluminium and are orders of magnitude more sensitive.

Olly

Edited by ollypenrice
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There's nothing fancy about the recommended cleaning brews. Distilled water mixed with isopropyl alchohol availabe at a chemist plus one tiny droplet of washing up liquid. Nothing to it.

Thanks :) regarding the cleaning brew. Don't you have to get exactly the right proportions of each in or you'll have too much water/alcohol? Do you think this is a better bet than wonder fluid for the corrector?

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This will be helpful for me too.  I recently bought a 2nd hand 8" SCT and there are watery type marks on the inside of the corrector plate.  I'll get some picture up tonight maybe.  The previous owner had left it his conservatory for a couple of years.

Thanks, Colin.

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This will be helpful for me too.  I recently bought a 2nd hand 8" SCT and there are watery type marks on the inside of the corrector plate.  I'll get some picture up tonight maybe.  The previous owner had left it his conservatory for a couple of years.

Thanks, Colin.

Yeah I've noticed condensation forming inside the plate at night too which is making me worry about its internal state, but the thought of taking the plate off fills me with so much dread I'd prefer to clean the outside of it in place and hope that does it. I've been storing it in my garage in a polystyrene lined box but I'm thinking now its clearly too cold and damp an environment for it. 

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I store mine the same way.  I'm thinking of keeping it in the house now along with my eyepieces.  To be honest i don't really fancy taking the corrector plate out either.  I'll maybe leave it a while and see what celestron would charge for a service.  Might be worth doing every 2-3 years.

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I store mine the same way.  I'm thinking of keeping it in the house now along with my eyepieces.  To be honest i don't really fancy taking the corrector plate out either.  I'll maybe leave it a while and see what celestron would charge for a service.  Might be worth doing every 2-3 years.

Yep me too. Its going to its new home in the cupboard under the stairs as soon as I can clear enough space for it. Regarding a service, do celestron offer one? I can only find Telescope House at the moment for telescope servicing and they seem to only do meades. 

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Hi Guys, I keep my scope in the shed - which is nearly at the outside temp - not sure if you want to bring a cold SCT into a warmer environment, as this would only create even more temp imbalance, creating even more moisture to deal with.

I know we want to keep our scopes in tip top condition, but this is a fact of life that it really doesn't matter how much we care for our scopes its inevitable that if you store a scope (especially a closed tube SCT) there is going to be moisture forming from the process of temp change - I find that storing it to as near outside temp as possible the best solution - I'm on my second SCT now and have found over the years that this to be the best solution - yes you do need to clean the corrector - have done this a few times - just take care and follow the steps regarding marking the corrector, keeping the tube pointed slightly down and concentrating on the inner surface to start with - replacing the corrector aligned to your marks.

My first SCT was over 5 years old when I sold it and just as good as "first light".  Don't beat yourself up over it - its a natural fact of life that closed tube scopes suffer from this - the bigger they are - the more they suffer, take your time it will be as good as new.   Paul.

Try and do it yourself if you can because I would worry more about the transportation involved, than the actual cleaning. 

Edited by Northern Soul man
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Thanks Paul, good advice again. I do understand what you're getting at re: storage of the scope. I could probably address how I store it in the garage as easily as finding a place for it inside. And you're right the temp difference will be huge when taking it outside producing a lot of condensation as it cools. I'm fairly happy now to clean the corrector plate, though still not intending to remove it, but the mirror is still bothering me. I still don't know how detrimental the few small splodges will be to my images. Guess I have to clean it and see as there's no way I'm taking it apart and attempting a mirror clean myself.

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Yes, As already said the mirror could be cleaned, but as already said, the coatings are totally different - looks as though the spots don't seem to contain any fungus - it just maybe water based - not sure that when the mirrors are made that they get a hardened silica "overcoat" placed on them after aluminising (the same as most of the newt mirrors) would be worth you trying to find out - would have thought that a water based solution similar to whats used on newt mirrors would work and having no active ingredients - just pure distilled water (if there is such a thing).

 Just looking around there seems to be SCT's that are some years old now and the optics look fine in them, but you have to be very careful as the coatings and over coatings have changed - some say not for the better - its just cheaper for production purposes - I think Doc Clay knows what he is talking about so I would research this a little more.  Paul.

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I agree, according to Doc clay most SCT mirrors aren't protected and I can't find any info about the C8 SGT XLT series coming with protected mirrors. Great :( Looks like I've got the toughest cleaning job of them all. Also looks like i'm going to need to dismantle the whole thing first as most people agree that mirror needs doing.

In short… I'm scr*wed  :p

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http://www.celestron.com/astronomy/technologies/starbright-xlt/

Hi don't panic here's a link to the coatings its all in a name!! the xlt coatings are used on your scope as with all the new ones now - not had time to look through it - it looks like the main mirror has localised spots so you could try doing the main mirror whilst in the scope - but check the coatings first and just use the weight of the cotton wool and don't apply any pressure at all.  I'll have a read.  Paul.

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Hi, I've just had a quick read and the coatings seem to not be over coated for protection so be very careful - might be worth you holding off a little - wait to see if anyone has cleaned an SCT mirror to post on here - someone, somewhere has cleaned one before - the spots on the main mirror seem localised - so I would try to clean with the main mirror left in situ and while you have the corrector plate off if that is what you decide to do - but remember EVERY SCT owner has the same problems as you - its down to the design of the scope and not the owner!!!.   Paul.

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Paul, you have become the legend of my thread :) thanks for the help, much appreciated. I'm going to tackle the corrector plate in situ for now and I'm also going to try contacting some specialist dealers to try and find one who can take on the job of doing the mirror. Unless, like you say someone posts here who has done a mirror before and its really easy (it won't be) but I know its not something I'm anywhere near the stage of tackling.

Its just soooo frustrating when I look at my grubby optics. I just want to give them a good rub down! Sigh.

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