C14 Corrector

[netwolf]

Hi All

This a C14 that my friends and I acquired as a project to restore. It's a black tube starbright coatings from either late 80s or early 90s. The front was very dusty and dirty but surprisingly came off easily with dabbing distilled water. The back is another story. Speaking to Dr Clay who is really a nice guy with fast responses. He advised it looks like mildew to him and not out gasing. I have also spoken tok Don at Bintel another great bloke (helped me many times) with my questions and cleaning optics for me in the past. Don said to try the uhtc same stuff as Dr Clay's mixture. We are going to give this a whirl.

One thing we did not was a small dab of 99% isopropyl seems to clear it for a short time when the alcohol evaporates the haze is back.

Anyone seen anything like this and has any success. Appreciate any advise feedback.

Thx
Fahim

[Wavytone]

Optical coating is peeling off - I’ve seen similar on old pairs of my (coated) specs - the old pairs I keep in the garage.

Every optical coating has microscopic pinholes which allow molecules of water to get in between the coating and the glass substrate. While it may look great at first, the pinholes slowly grow with time inevitably (humidity) or made worse by well-intentioned but counterproductive cleaning with solvents - starting with water or anything else.

If you want the scope to last:
- best to keep in someplace dry with a cover that breathes;
- resist the urge to clean the corrector unless it’s absolutely necessary.

New corrector required, you have the link I sent previously. Celestron may also offer to supply a corrector.

FWIW I’m pretty sure Celestron and Meade SCTs are not matched sets - they slap together whatever comes off the production line, and they aren’t doing much of a quality check either - the average scope has p-v wavefront errors around 0.36 wavelength - not even ⅓ wavelength. Meade is a bit worse at 0.4.

[Merlin66 (Ken)]

Wavytone,
I’m surprised to see your figures for the optics on the SCT’s....
Do you have a source??

[Wavytone]

See https://www.cloudynights.com/topic/6...or-myth/page-3

There’s a link to a Russian optical lab that did the tests, each set of results, interferogram and a photo of the scope (sometimes with owner) are posted. I’ve pulled out the SCT and maks from Meade Celestron Skywatcher Intes and Santel into a spreadsheet, can post it later.

Using the filters you can compare SCT vs mak, Meade vs Celestron etc. Doesnt make much difference if you use P-V wavefront error or strehl.

If it’s a reasonably random sample and I don’t see why it isn’t, it also implies a lot of the claims on CN are balderdash.

It also suggests you’re getting nothing special by shelling out for ACF or HD optics...

Another aspect is that if you omit the 3 worst shockers for each of Meade and Celestron things look decidedly better. But it does confirm they do sell the crap scopes with wavefront errors close to a wavelength !!

[multiweb (Marc)]

I'd listen to Don at Bintel. Given the scope is circa 90 I'd say it's a matched set so be very careful with the corrector and do not overtighten it when you put it back. Just touch pressure on the retaining ring and set them back in a star pattern when you secure it. 12 o'clock, then 6, then 9 then 3, then 10 then 5, then 2 then 8, you get the idea.

[Wavytone]

Ken i've attached the spreadsheet to the thread on CN. You will need Excel.

[E23 (Andras)]

Fahim

I had/have the same mildew(?) on 1/3 of my C14 corrector a few years ago also 1990s vintage. I gave it to Don at Bintel to try and fix it. Ah yes the scope also had about a 1/2 a cup of water inside due to an unfortunate rain accident. Don cleaned it up pretty well for a very modest fee except for a small hazy area left on the corrector.

Andras

[casstony]

You could try acetone, which is much more potent than isopropyl and tends not to leave residue behind. I've used it occasionally for stubborn grease/oil stains or sap deposits.