Cleaning SCT corrector plate

[Tenor Viol]

Having retrieved my 40 year-old C8 from out of the garage, de-forked it, and mounted it on an HEQ5 with a dovetail... It's apparent that the corrector plate needs cleaning. It looks like a lot of it is on the inside (it's been in its case in the garage for over 21 years untouched).

I've never taken it apart before. Can someone point me at any suitable resources about dismantling the corrector plate assembly and cleaning the inside? I've had a trawl through Youtube, but they all seem to gloss over the details of disassembly. I think I'm OK with the basics of cleaning.

It looks like this at the moment - seems to have a film on the inside. The primary looks to be OK.

 

[Stuart1971]

Hi,

first of all put some bits of tape on the retaining ring and onto the inside edge of the tube so you can put it back exactly the same way, then when you remove that ring, but a mark on the edge of the glass and also on the inside of the tube, so you can put the glass in exactly the same orientation, there may well me a mark already on the glass as this is usually done when built.

then there should be some small cork or maybe other material, packers around the glass, don’t loose these, and make sure you put them back evenly around the glass

then holding the secondary housing remove the glass, but do this with the tube horizontal or slightly pointing down, so no bits go inside the tube, clean with a brand new untouched micro fibre cloth with Baader wonder fluid, spray it on and then gently wipe over until the liquid has evaporated...
Then fit back by doing the reverse, it is very important to put all back in the same orientation as it was....

HTH 👍😀

[John]

This might help. It goes further than you need to but the part about the corrector is relevant:

https://astromart.com/reviews/telescopes/show/disassembly-of-an-sct-childs-play

[Peter Drew]

You may well find that the corrector plate on an elderly C8 will be reluctant to pull out, if this is the case, replace the retaining ring loosely and then tap round the exterior of the tube smartly with your hand.  The old C8's corrector plates were not edged perfectly round and cork spacers could be different sizes and at random looking spacings, might be a good idea to photograph the arrangement to facilitate their eventual replacement.  The film is usually the result of outgassing of the original interior paintwork.  I have also seen a similar appearance where the instrument has shared the environment of heavy smokers!        😀

[AstroTim]

I don’t know how the older OTA’s are put together, but it might be easier to remove the whole front end section with the corrector still in place (not sure of the correct term) by undoing the screws around the outside edge of the tube (check if they are plain screws, or have nuts on the inside first though). That way you don’t risk misaligning the corrector or any of the packers etc. (you will still need alignment marks on the tube and end section so that you put it back in the same alignment, but at least it’s only a matter of aligning the screws with the right holes). You might not be able to clean right to the absolute edge of the corrector this way, but it may well be good enough and the overall task will be simpler.

Regards,

Tim

[AstroTim]

The above was based on a quick look at my C5, which uses just screws (no nuts) to hold the front section on to the tube. Reading through the link posted earlier, it looks as though at least some OTAs use nuts on the inside as well, so the above wouldn’t work in those cases (while you could possibly use a spot of glue to retain the nuts in place for reassembly, you risk them dropping onto something fragile during disassembly).

regards,

Tim

[billhinge]

Also  you may want  to read the cautionary tale here before you take the front off  https://www.cloudynights.com/topic/663447-apparent-need-for-hotech-sct-collimator-because-celestron-does-not-assemble-their-edges-correctly/?hl=carbon tube about total mis-alignment of front and back  (note hotech users there is a new manual v9 - site still shows v8)

I have a hotech by the way and I used  protostar flockboard  - draw your own conclusions 😂

 

[Starwatcher2001]

This looks like a good resource: "How to strip and clean the optics of a SCT (Schmidt-Cassegrain Telescope)"

https://www.youtube.com/watch?v=e66yIuD3cMk

 

 

Edited August 6, 2020 by Starwatcher2001
Link fixed (I hope)

[inFINNity Deck]

I used that video to clean my C11 EdgeHD and it is quite easy. Baader advices to use colour- and odourless Kleenex tissues, which I did use, worked like a charm.

Make sure your workspace is properly prepared, so that you know where each piece (screws, retaining ring, corrector plate, etc.) is going to once taken from the OTA (and where all your materials are). A small sturdy table helps for cleaning the corrector both sides, I used a large square flight case for this.

Finally, and perhaps most important: take your time, do not start this job an hour before lunch, dinner or any other appointment.

Mind you that a broken corrector plate cannot be replaced!

Good luck!

Nicolàs

Edited August 6, 2020 by inFINNity Deck

[Tenor Viol]

I might be doing mine tomorrow - I'll be setting aside a whole afternoon. Might defer it if it's too hot.

Edited August 6, 2020 by Tenor Viol

[JeremyS]

49 minutes ago, Tenor Viol said:

I might be doing mine tomorrow - I'll be setting aside a whole afternoon. Might defer it if it's too hot.

Good luck! Let us know how you get on.

[Tenor Viol]

10 minutes ago, JeremyS said:

Good luck! Let us know how you get on.

Shall do

[billhinge]

Took my corrector off and started cleaning. 

I hadn't used my C11 for about 7 years and there was a ring of smeared cleaner (alcohol based) around the plate causing a purple discolouration. Two afternoons of patient dabbing with distilled water and a little soap seems to have removed 99% of the residue. Almost as good as new now. Seems these alcohol cleaners are a bit hit and miss (I  have a big bottle of pure acetone just in case)

Mirrors look good so not touching them

I had flocked my tube with proto star flockboard some years back, still looks good. Next step to give the corrector a final clean and re-collimate (with Hotech)

Still pondering whether to drill the tube and tap the holes with 3 corrector centering derlin tipped screws (from the finder 😉

Hopefully my  Feathertouch focuser will arrive soon, it will get motorised with a Primaluce motor

All that done its almost like getting a new planetary scope for nix  (I fell out of love with it in favour of an easy to use small Apo triplet)