Call Out For Help, Cleaning Inside C8 SCT

[Aussie_Dave]

G'day all. Is there a senior experienced member in the Peel Region WA that could help me clean the inside of my Celestron 8 SCT corrector plate? I've never done it before and researching online tells me that it's not recommended. I'm just worried about taking it apart and putting it back together correctly.



The problem is I tried to clean the little bit of dust that was inside on it with a can of CO2 and what I've actually done is made all the dust that was in the OTA now sit on the inside correcter plate glass, I've made it worse It looks like it has been taken apart before as there was some marks on the inside already, smudges etc. It needs to be collimated anyway so I'd rather clean it up as best I can first.

If there's anyone out there that could help me I'd be very grateful.

Cheers.
Dave.

[astronobob (Bob)]

Hi Dave, I wouldn't fret too much, it not difficult, tho Im not from the Peel Region WA, but cleaning scope optics is very common practice in astro community, most warnings of seeking experience help is to have peeps aware of just a couple of basic precautions. 1st is, Not to use strong solvent cleaners on optic surfaces - recommendation of a camera lens cleaner is fine with corrector lenses as on your C8, tho don't use it on you main mirror - main mirror if you decide to clean is done in warm water with a couple drops of dish detergent, and only very lightly swished with a cotton ball while mirror is totally submerged, then rinced of well with tap water, the rinced again well with distilled or clean rain water !
With taking off the corrector lens, youll need a very well fitting allan key wrench, if that's what needed, - mount the scope so that it is pointed slightly up any amount is fine, 20-40degs is ok, undo the screws around the corrector holder ring - Mark the ring at the 12' O'clock position before taking off, move the ring away a little at the 12 0clock top and mark the mirror in the same 12 oclock point & also mark the Tube at 12 oclock - these are you reference point to reassemble correctly . .

Clean your mirror this way ; in a cool shady place, inside house rather than outside to avoid dust in wind etc, using a camera lens cloth or clean 'micro fibre' cloth and camera lens spray cleaner.

Avoid spraying the Secondary Mirror with lens spray cleaner, ) I usually cover the 2ndary with a pressure pack lid while I spray, then take it away !
Spray lens very lightly with cleaner, don't soak it, just a quick spray to form a light mist all over, then promptly tho lightly with the lens cloth, start from the center of lens with a spiral motion to the outside, and that's it. don't rub as you might with getting a dry bug off your car windscreen - if you have a stubborn mark, maybe use a cotton bud, and spray cleaner onto the bud so its wet, and dab the spot a few times and allow time between dabs 3-5secs for spot to absorb the cleaner, if after a few times, try a little pressure with cotton bud to see if spot is moving, if so, promptly spray lens spot area again and wipe away to the outside edge with lens cloth, if spot remains, leave it there as it wont effect performance much at all if any !
Reassemble with care lining up your marks and all should be fine - tho, don't over tighten the screws as may crack the corrector, hand firm is all it needs...
Hope this is usefull
Rgrds

[TechnoViking (James)]

I was in the same predicament last year, I was worried about pulling apart my 9.25 sct, but i bit the bullet and cleaned it. Its not overly difficult to do just be patient and methodical.

I used the recipe for the cleaning solution on this site.
http://www.astrosurf.com/luxorion/reports-cleaning.htm

The proceedure took me 3 hours, because I was being a little too cautious, but the end results were worth it.

Good luck!

[Aussie_Dave]

Thanks guys, have taken note of suggestions and bookmarked the link.

The previous owner must have stored it without the cap or eyepiece in the visual back for some time. I've only just acquired it and the outside OTA and mount/tripod was worse. I'm going to have to clean everything inside now which is probably a good thing. I don't want to do it but honestly if you saw it, you'd do the same. I was more concerned about the reassembling part and getting that correct. I did read somewhere about marking everything before taking it apart.

Once I've done it for the first time, I should be alright for my other 8" that may need cleaning in the future but that one only has a few specs of dust inside. I'm not going to worry about that one for now. I can live with that.

I don't understand how some people can treat and store their gear like this. How hard is it to put it in a box, tape it up or put a plastic bag over it.

[Aussie_Dave]

Well I decided to take the plunge and do my first clean. It wasn't as hard as I thought or what people make it out to be although I did run in to a couple of issues.

The first being one of the spacers, which seem to be very small longish rectangular cardboard, 2 different thicknesses around the corrector plate. One of these actually came out when I was blowing it out last week with the can of air, which I shouldn't have done in the first place. This was most likely forgotten from the previous owner having it apart. I'm not sure where that spacer went. The spacers that were there I took photos of and replaced them back to the correct locations however there still seems to be very slight movement in the corrector plate once putting it back together with the spacers.

The second issue was while cleaning the dust off the primary mirror I accidentally touch it with my finger knuckle a couple of times which then left a smudge, even though my hands were clean. I would recommend anyone doing this to buy a pair of those thin white cotton gloves before cleaning the primary to avoid accidentally touching the primary.

The clean went ok and inside would be 70 - 80% better than what it was but I will need to do it again and clean the primary mirror properly when I buy some distilled water during the week. The only way to get it to anywhere near 100% clean and dust free would be in a dust free laboratory environment.

Overall I'm happy with the end result but will do a better clean during the week on the primary mirror.

[astronobob (Bob)]

Interesting Dave ..

I must say I haven't come across any cardboard spacers near the corrector holding ring ? ? seems a bit strange on a couple accounts, 1st, the corrector and ring should have already been manufactured to fit flush within the tube end recess, 2nd) I would be carefull doing up the retainer ring screws if its been 'propped' by some cardboard, may cause some undue uneven pressure to the corrector glass ? ?
In saying that, I have only had one C8, tho I doubt if the cardboard's would have originally come with the scope when new, seems rather unprofessional ? ?
Anyway, others may chime in and correct me if Im wrong

Another point of view about dust on mirrors, Personally, its not essential to have a mirror 'totally spotless' tho an SCT looks better if you cant detect any at 1st glance, either way, a few specs will definitely Not impede on performance - also, cleaning mirrors over and over is not good as even evry time you clean a mirror, even with the proper clothes and fluids, you will always be making very tiny micro scratches, hence, lightly clean surfaces I personally consider that a few specs does not warrant another wiping session , but all to their own It not totally critical, tho it is rather common knowledge that the fewer mirror cleanings the better

Sounds like you have done a good job all the same, tho, Id probably get a second opinion on those cardboard strips ?
But rest assured, I dont mind being wrong

Rgrds

[Aussie_Dave]

You are correct in your thinking Bob. The spacers are not the original, the lengths are different and a couple of different thicknesses which initially worried me. The movement in the corrector plate is about 1mm or less with those cardboard spacers in, and that's 1mm too much. I had a quick look through it once I put it back together during the day time and it's a surprisingly good, clear and sharp image although looking at the stars is another story and I'll most likely need to adjust the secondary to get it spot on.

I've never used a collimator before as I've never felt I needed to, mostly had 8 and 10" reflector dobs, 4 to 8" reflectors on EQ mounts. There seems to be a little play with both my standard collimator and my laser collimator, pointless having them really. I'll do the out of focus bright star adjustment on the secondary as it's the most accurate for me.

I bought some David Gray's distilled water yesterday. I'm looking to do the primary mirror clean tomorrow when I get a spare hour or two. Just trying to work out the ratio of water to dish washing liquid... and which brand as they are all different :/

[Aussie_Dave]

I just need to mention Bob that the spacers are only around the edge of the corrector, not between the corrector glass plate and the corrector holding part (which is attached to the OTA). The ring that goes on the front of the corrector plate to hold it in place, I haven't done the screws up tight, enough to hold the corrector plate in place firmly.

I didn't want to clean the primary but after using the can of air and then touching it twice with my finger knuckle now warrants a proper clean. It's the primary that has the Star Bright coating on as well so something else to be extra cautious of. I'm not looking forward to doing it. Micro scratches is a bad word, fingers crossed.

[astronobob (Bob)]

Sound like your in control Dave, clean glass, a collimation = good stargazing
Re, micro scratches, Lol, no need to worry mate, tho theyll add up if one is inclined to clean every month or two, would degrade performance in a couple of years !
As with water and detergent, doubt there be a specific ratio ? more just common sense be a good guide, an oily fry pan need a good squirt, a mirror need a couple/few drops sought of thing
Should be some tutes or even youtube demos, tho I seen one where a guy just wipes over the mirror under running tap water with a dish cloth, Lol, fair enough but that mirror wont last many years
All the best

[Aussie_Dave]

Yeah I've been searching for some days and there isn't a standard formula/ratio and I have seen and read some iffy stuff. There's also alcohol that I have to add to the mix apparently.

What I did come across was a page from Celestron themselves on one of their support pages
http://www.celestron.com/support/kno...ctor+plates%3F

Funny thing is, they recommend using compressed air By the look of it inside, I'd think it'll be it's first clean. Once it's done, that's it. There shouldn't be any need to do it again if it's stored correctly.

As far as I can work out like you say, it all comes down to common sense. I think I'll be right