Cleaning an SCT

[ChrisCM]

Hi Guys,

As noted in a previous post I am resurrecting my equipment after a break of 10+ years. I have now got round to my Celestron 9.25 SCT. The corrector plate has a couple of marks , they appear to be on the inside. I have no idea what they are, look almost like bird droppings? (But obviously not!) The larger mark, on close inspection seems to be a ring of smaller marks. The mirror appears to be spotless. Is it easy to remove the corrector plate? I realise that I would have to re collimate. Any advice gratefully received!

Here are a couple of shots of the marks, you can see them at about 2 o'clock.

 

 

Thanks for looking

Chris

[Freddie]

I wouldn't bother. It shouldn't make any difference to optical quality and you could end up with more problems than you have solved unless you can get the corrector back on in perfect position which isn't impossible but isn't easy.

[Peter Drew]

I totally agree with Freddie, compare the size of those marks with that of the central obstruction of the secondary holder next to them.

[SkyBound]

Hi,

i have had similar marks on a Celestron SCT after years of storage and not being used, and had to remove the corrector and clean.

it was quite straight forward, make sure it is tiller slightly upward first of all, then remove the retaining screws, and the plastic retaining ring, it is in two parts so make a mark on both ring and scope so you can put back the same way, there are also cork spacers make a note of these along with orientation and lastly mark the edge of the glass and the edge of the tube so that can be put back in exactly the same spot, then remove by gently pulling on the secondary assembly.

it is very east and straight forward, I cleaned with Baader wonder fluid with a micro fibre cloth.

hope that helps

[SkyBound]

Actually as the others have said the marks won't make any difference to views but I hated seeing them all the time, so had to clean mine, especially as I have a touch of OCD

and it looks like your retaining ring is in a single piece, and not two parts.

[ronin]

If it is on the outside of the corector then clean it carefully, not 100% sure what carefully means to you however. One place I know of it means inspect the bit of tissue for the cleanest patch and breathe gently.

If it is on the inside I guess somewhere like SCTelescopes is a good idea. Steve (think it is Steve) services SCT's and Maks and others so knows how to get into them and then (usefiully) put them back together. Sometimes the silvered internal mirror is not well protected and cleaning can damage that. Then you no longer have a scope.

[ChrisLX200]

Speaking personally, I would disassemble the corrector and clean it - something I've done many times with my 10" SCT. The reason to suggest that is because it may be a fungal or bacterial growth which could potentially spread, and it will eat the coatings and even possibly etch the glass itself. There is no risk involved with the job provided you can follow instruction and are reasonably competant with your hands - otherwise get someone else to do it

ChrisH

[Northern Soul man]

As mentioned previously its 10 years old so when taking the corrector off just mark the front of the corrector and the inside edge of the tube assembly with tape or something just to line back up later, you may have cork spacers around the outside of the corrector so if its staying put after applying gentle pressure to remove the corrector just soak the cork spacers with a little alcohol to free it but you may be ok, as mentioned its an easy enough job just be sparing with the cleaning fluid and keep it off the primary as I think these are not silica overcoated, if you still have smears after just use a little breath and gently does it over the years ive done all my sct's and never had a problem its just part of the sct maintenance the views through mine are still stunning .

Paul.

[ChrisCM]

Hi Guys,

Thank you all for your views, I really didn't  want to dissemble it but the only thing I can think it is is a bit of fungus, if it is then as ChrisH says it's better out than in otherwise it may spread. I tried recently to obtain some isopropyl alcohol but my local pharmacy said it's no longer available to the general public, can anyone suggest a substitute as most lens fluid cleaning "recipes" seem to include it.

Noted the reference to Baader Wonder Fluid, I'll look into that if I can't find a substitute for isopropyl alcohol, but does look rather expensive for a 100ml bottle?

Chris

 

[Alien 13]

8 minutes ago, ChrisCM said:

Hi Guys,

Thank you all for your views, I really didn't  want to dissemble it but the only thing I can think it is is a bit of fungus, if it is then as ChrisH says it's better out than in otherwise it may spread. I tried recently to obtain some isopropyl alcohol but my local pharmacy said it's no longer available to the general public, can anyone suggest a substitute as most lens fluid cleaning "recipes" seem to include it.

Noted the reference to Baader Wonder Fluid, I'll look into that if I can't find a substitute for isopropyl alcohol, but does look rather expensive for a 100ml bottle?

Chris

 

Maplin sell IPA in 1 litre tins I think, 99.7% pure. This http://www.maplin.co.uk/p/isopropyl-alcohol-1-litre-re71n

Alan

[ChrisCM]

Thanks Alan,

I'll pop into the local Maplins!

Chris

[SkyBound]

Here is one I bought a while back

http://www.ebay.co.uk/itm/ISOPROPYL-ALCOHOL-IPA-ISOPROPANOL-99-9-VOL-250ml-/142147981698?hash=item2118ae1182:g:49sAAOxyJX9SJ2CK

although mine was in a small pump spray bottle which is ideal.

[Alien 13]

I had a similar problem finding it locally you will probably need to dilute it with distilled water, good luck with finding that although RO water should do.

Alan

[Phil Edmonds]

FWIW. I have had perfectly good results on my C9.25" corrector  just using very dilute Fairy Liquid (diluted 2 or 3 drops in a teacup with de-ionised water from Halfords) followed by rinsing with de-ionised water. I found using any alcohol-based product left smears. I use cotton wool balls, tiny light pressure twists, no more than an eigth of a turn at a time, then the same with soft tissue for the rinsing stage.

[Peter Drew]

1 hour ago, Phil Edmonds said:

FWIW. I have had perfectly good results on my C9.25" corrector  just using very dilute Fairy Liquid (diluted 2 or 3 drops in a teacup with de-ionised water from Halfords) followed by rinsing with de-ionised water. I found using any alcohol-based product left smears. I use cotton wool balls, tiny light pressure twists, no more than an eigth of a turn at a time, then the same with soft tissue for the rinsing stage.

I too, have gone back to using Fairy liquid to clean large optics as the Wonder Liquid left difficult to remove smears. I don't know if I've been doing it wrong as others report good results, it seems to work well on small items such as eyepieces.

[Alien 13]

Grease spots often get spread over the whole surface with IPA based cleaners, if its a small area effected then I have had the best results by using a lens pen with a single swipe.

Alan

[ChrisCM]

Rather than Maplins I've now ordered a litre from Amazon, free delivery too at 1/2 the price!

https://www.amazon.co.uk/gp/product/B003D8QFR8/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1

When I've cleaned lenses before I've used neat isopropyl alcohol on any stubborn bits, gently wiping with a soft lint free tissue, changing between wipes then flooding with distilled ( from my de-humidifier) water again wiping with the lint free tissues. When dry a blow over with a rocket bulb blower to dislodge any specs of dust which may have landed.

I reckon that's  the easy bit it's the dissembly/reassembly I'm not looking forward to ?

 

Chris

[Tyson M]

Windex, distilled water and a touch of rubbing alcohol. 

Doesn't streak with the windex. Otherwise it can be a pain, with wipes or with a distilled /rubbing alcohol mix

[ChrisCM]

I'd be careful with rubbing alcohol, here in the UK its known as Surgical Spirits, it's only 70% - 90%  alcohol and can contain up to 2.5% castor oil + other "goodies". Isopropyl alcohol can be obtained, typically 99.7% pure with the balance water. Not sure what windex is, I've seen it mentioned on other US based sites, not seen it here, I wonder if it's the same as windolene a window cleaning liquid?

I wonder if a couple of drops of wetting agent, as used when making photo negatives/prints, in the final rinse would stop streaking on the lens?

 

Chris

[Jupiter1]

I could not agree more with the advice on using fairy liquid ( only min amount with Distilled water. ) I have Ltrs of Isopropyl  easily bought on line and Far cheaper than shops.

 

Celestron  recommend  60% with 40% Distilled water but I have found that this will Still leave smears when held at an angle in the Sunshine. It depends how critical one is.

I have ended up using Distilled water alone on a soft tissue and then breathing on the glass and that will soon show any smears. I am super fussy with optics ! Any deposits left on the lens could etch into the coating as others here have suggested.  Just mark positions if you want to remove the lens and remember it is important to place the secondary exactly in the centre for top results , Best of luck,   Jupiter 1