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Calling all Celestron C9.25 Users - your opinions please


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Whilst inspecting my C9.25 (which is only 10 months old) with a torch I noticed some "smearing" on the inside of the corrector plate which I show in the attached photo. 

When you look down the tube without a light source you cannot see anything but apply a torch and you see this. I think that it's grease as it looks like someone tried to clean the corrector when assembly took place and left these smears. 

My question is - in your opinion is this worth taking off the corrector to clean or is it best left well alone? It's definitely not condensation and I always use a condensation cap when the scope is not being used. I think that I could probably cope with the work required to clean the inside but I really don't want to unless I have to.

Any advise or opinions would be welcomed. Thanks in advance.

Peter

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When I've had my C9.25 outside for a while and the dew/condensation starts to take over I've noticed that smears and dirt become visible.  The humidity does have to be quite bad though before it starts to affect visuals, and usually the eyepiece gets fogged long before this.

Are the marks visible all the time, or only when you've been outside?

Personally I'd leave well alone unless it is distorting or blurring the image.

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Thanks Jamie. The marks are visible all the time IF you shine a torch at the corrector. Just looking at the corrector under ordinary light or at night and you cannot see any marks. I don't know if it's blurring the image as any blurring could just be due to seeing conditions.

Peter

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I've just shone a torch into mine to see if it's the same or not.  I wish I hadn't.  Dust all over both the mirror and corrector!  There are no smears though.

Is it still under warranty? You could ask the supplier?

This is actually my second C9.25, the first one I bought had to go back because the inside was dirty.  For the money you'd think that they'd be more careful when manufacturing.

You could try setting up and focusing on something in daylight.  That might show if the views are clear or not??  Just a thought!

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I can't see any marks on mine. Apart from the usual dust it looks clean.

You wouldn't have to take the corrector off to clean that. If you are careful, you could take the secondary assemby out and clean those two bits through the hole. A tight fit but do-able. Much better than taking the corrector off as that is fraught with danger.

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Hi Peter, good advice from above AS USUSAL (Just as you would expect from this great bunch)!!, as Jamie says, I would leave well alone, If it were grease I think Peter, you would see a residue without torch light (being oil based) - these SCT's could well be assembled in a clean environment, but its inevitable that your going to get some sort of "contamination" on the Mirror/glass surfaces - we use these scopes under really bad conditions when glass/mirrors are there if you think of it, when the dew takes over - which it is going to do - your just not going to be able to stop this "natural" phenomena occurring - its how things are.

When I've been out for a night under the stars and the "mist" begins to appear, it makes all sorts of patterns over the corrector - this is how the smears tend to form - its not full on moisture, but the begining's of it - the dew heaters (my Astrozap never really gets that warm to the touch) prevent "full on" moisture but if your observing on a really "wet" night - its inevitable that moisture (even very "dry" moisture (dry at the point of it just beginning to form) is going to form as its a very fine temperature imbalance which creates this "natural " occurrence - the bigger the corrector's - the more prone they are.

I've had my CPC well over 2 years now and have cleaned the corrector only once, its easy enough to do (just very daunting thinking about it), I had my 8" SCT for over 5 years I think, I only cleaned that a couple of times - I'm methodical when I clean - marking the corrector and outer casing to line up again after - the secondary is very secure in its holder - so no problems with the secondary moving in its housing.

I've got to the stage now where i'm not bothered about dust on the corrector - EVERY SCT owner is the same - we all use our scopes in the same way, but temperature change, for me, is kept to a minimum (BUT STILL get dew on some nights!!) - with the  scope stored outside in a concrete shed out of direct sunlight - this has been the way for me for my, now, second SCT and all is well - the views still blow me away and really fine detail on Jupiter is still being observed - so if your careful - a corrector clean is well within your "scope" of things (pardon the pun).

I see the scope is still under warranty - not sure if you purchased it locally or over the net, I would be more worried of sending the scope "through" the post - remembering that it also has to be sent back to you - so you have to decide - but from the pics - I don't think its oil based - you would notice this under a flashlight - but as mentioned keep the torch well away from the optics - the first time I done it, it gave me nightmares!!

Paul.

Just a point though, I have seen pictures of 20 year old SCT's and they still look great - but I bet have been cleaned a few times.

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Paul - Thanks for that. Yes the scope is only 10 months old but I have voided the warranty by changing the focuser for a Starlight micro and added Bob's Knobs as I was struggling with the Phillips screws (earlier post). I have tried the daytime test but to no avail as I cannot see anything that's far enough away and the weathers not too good at the moment (surprise).

I have approached the supplier in Surrey and am awaiting a reply.

I might have a go at cleaning the corrector someday but I am worried about it sticking to the gasket underneath and damaging that in the process. Did you have any issues like that when you have carried out your cleans?

Peter

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Hi Peter, Thanks, no - not at all, the only gasket that's under the corrector in my CPC is a paper gasket, not even attached to anything, in fact I think that it is in 2 pieces which you just align under the nearest holes in the cover with the writing on where the screws go through which surrounds and holds the corrector.  The gasket is quite thin and doesn't even "cushion" the corrector - my scope was bought in Feb 2012 - I would have thought the design hasn't changed much.  The Meade 8" LX 90 I had, had a cork gasket, but it was not stuck down, this was more of a cushion than on the Celestron.  I think there were earlier posts regarding this cork gasket (I think this was used in the Meade I had and not the CPC) being attached to the corrector, I think the gasket was soaked in Alcohol to free it, but as said, on my 1100 its just a slip of dark paper which goes between the corrector and its housing - I think its just collimation which lines everything up afterwards - you just adjust the angle of the secondary to "centre" the rays of light (I think??) .

Remember the actual focus point of the mirror/lens system in an SCT is a very long distance away from the actual corrector - the focus point just sits below the EP, the actual mirror is moved to achieve focus and everything is bought to focus "under" the EP - so any smears/dirt on the actual corrector are a long distance from the focus point (so I think would not show)and you would need a massive amount of dirt to actually degrade the views as far as I can gather.

I was looking at the double shadow transit and the GRS transit the other night - the seeing was very good for a change and the detail I could see was spectacular - I even "hibernated" the scope in between the moon and GRS transits to go in for a warm - I can assure you that the corrector removal has not altered the views one bit - I'm picking out detail in the polar regions when the seeing is good - and its THIS seeing which would degrade the views far more than a few smears on the corrector.

Paul.

If you do try the clean just remember to mark the corrector and the housing (I used a little masking tape) to make a "line" to hold corrector position, when replacing, just lightly pinch the corrector bolts up and make sure they're not too tight, if unsure when dis - assembling, point the tube facing straight up (to the zenith) just to check the position of the gasket, but when completely removing, I sit the tube slightly angled at about 45 degrees.

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Shining torches down scopes is not recommended. Now try it with a red LED light, like a bike rear light. Then you'll need a beer or two to calm down. Don't touch it, it is not degrading your view, after all you have got a huge secondary on the plate and you can't see that? My corrector looks like some folks have played twister on it and it still gives crystal clear views. :-)

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Hi Peter CPC - just had my 9.25 corrector removed and cleaned today thank you Peter at Todmorden Astro society. I have not touched the corrector in six years and it got pretty dirty, using the scope visually it was ok but my ccd camera would not come to focus. On focusing the Airey disc was perfectly concentric but the rings where 'fuzzy' which I think is down to a contaminated corrector plate.

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I have some haze on the inside of mine. It may be related to outgassing from the paint on the inside of the tube. They may assemble these quite soon after the painting process. I don't think it makes the slightest bit of difference.

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I can't see any marks on mine. Apart from the usual dust it looks clean.

You wouldn't have to take the corrector off to clean that. If you are careful, you could take the secondary assemby out and clean those two bits through the hole. A tight fit but do-able. Much better than taking the corrector off as that is fraught with danger.

I agree with michael, ive used this method a few times via the fastar, taking the corrector out is easy enough just mark the plate first to line back up on reassembling!

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take a note of the size of the obstruction vs the size of the smears, yes they may be annoying, but will not really be of an issue compared to the big obstruction already there by design.

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