Stripping down an SCT OTA

[toryglen-boy]

i got my hands on a great little 200m SCT OTA, and while its in great condition, i got to thinking, how would i get to stripping this down to clean it etc? i mean, is the corrector plate on the front matched? is it ever meant to be removed?

mehhh, what do i know


:lol:

[mick pinner]

the front correctors are matched to the primary mirror. be sure to mark the position of the corrector to the tube and make sure it goes back in the same place.
also be careful to note the cork spacers when removing the corrector and also replace these accordingly.
DO NOT overtighten anything when reassembling.

[Merlin66]

http://www.astromart.com/articles/article.asp?article_id=594
http://www.laughton.com/paul/rfo/c11-disasm.html
http://www.nexstarsite.com/OddsNEnds/SCTCorrectorRemoval.htm

Just google "cleaning SCT" for even more links!!

[toryglen-boy]

i know i could have googled it. I was really after first hand experiences from forum members.

but thank!!

:thumbsup:

[citivolus]

Correctors are easy to clean if the OTA is designed to be easy to open, as is getting any dust out of the OTA and blowing off the primary. Anything more than that I have yet to do.

People are scared of cleaning correctors, because it has a high intimidation factor. I think people have them pictured as a thin sheet of glass, which they are not. They are really quite thick. That said, remember that the OTA will become off-balance when you lift the corrector out, due to the lack of anything to counter the mirror weight.

Regards,
Eric

[toryglen-boy]

its kewl, it will be on a table top

:)

[marki]

Duncan I have cleaned my corrector on a couple of occassions (LX200) but only when it's really dirty. The procedure I follow is as follows.

1. Set up on a flat surface with plenty of room and have a soft towel folded ready to accept the corrector plate. Soft clean gloves will save you a lot of extra work and prevent oil transfer from your skin.

2. Point the scope upward for easy access and carefully loosen the bolts on opposite sides a little at a time (1/8 turn) until they are free enough to be wound out by hand.

3. Remove the retainer and make sure your corrector is marked so you can re-align it again, a must on a SCT. (mine has a thick white line with a black line in the centre drawn by a fine marker).

4. You need to be very careful when removing the corrector as it gets stuck on the cork spacers. I use a pop stick to gently apply pressure around the corrector until it comes loose. Before you take it out note where the cork spacers are and make sure they go back in the correct position if they come loose.

5. Get a good grip on the secondary mirror holder and lift the corrector out placing it face down on the towel and rotate the scope so it is pointing down to prevent dust from settling on the primary. I have a small plastic cap which fits perfectly over the secondary baffle which I use to cover and protect the secondary mirror. Think I got it off a new turbocharger when I was involved in racing :shrug:.

6. Try not to get anything on the secondary mirror as getting it off again will be very difficult without damage. I first wash the excess dust off under the tap and then rinse using de-ionised water then let it dry. I use the bintel UHTC cleaning fluid and cotton rags for the final clean on the corrector. The only trick here is to wipe in straight lines and use a new surface each time changing rags regularly.

7.When you are satisfied that it is totally clean, flip the scope back up and replace the corrector making sure it is aligned properly with the marks.

8. Replace the retainer and all the bolts by screwing them in with your fingers until you just feel light resistence. Use an allen key to tighten each bolt 1/8th turn at a time. It is important that you do opposites as this keeps the pressure even and does not stress the glass which will crack. You only need to tighten until you feel light resistence on the allen key, very little pressure is needed and the glass will stick to the cork. Use your noggin here as a busted corrector means a useless scope. Thats it.


I have never found reason to clean either mirror as they don't seem to attract dust like the corrector. I would never physically touch a mirror and would only ever rinse them with water if they got really really dirty. If you remove the secondary holder make sure you put it back in the same alignment as I am led to believe this is also essential.

Good Luck

Mark

[Don Pensack]

Here is a step-by-step rebuild with pictures:
http://www.skyimager.com/C14-rebuild.html
It's a C14, and the smaller sizes are the same, just smaller.
Remember:
focuser is disconnected first.
corrector is removed.
primary is removed
other mechanicals are taken apart.
You can soup up the SCT with a 2-speed replacement focuser from Feather Touch, fans in the rear cell, better grease in the inter-baffle space, and flocking the interior.
I've done several of them. It's really not as intimidating as you think. If you can collimate an SCT, you can take one apart.
You may not need to clean the mirrors, but everything else typically needs doing if the scope is older than ten years.