Milky corrector lens

Ric · #1 18-12-2006, 10:06 AM

Hi all, I have recently noticed that my 30 year old C8 is slowly developing a milky film on it's corrector lens, the problem is that it is on the inside of the glass.
The majority of the glasses diameter is good and this film is very light but around the edges the glass has taken on an opaque look about it.
It is only used for a few weeks every year while on holidays but is carefully stored in it's carry case at all other times.
Has any one encountered this problem as well or know how or why it's happening I would be very interested to find out more about this milkyness.

I dont think that it has affected the performance of the optic, but as I dont use it constantly it is a bit hard to judge.

cheers

matt · #2 18-12-2006, 10:46 AM

Sounds perhaps like a fungal problem, Ric.

Moisture somehow got into your scope and then you sealed it up without letting it dry out?

You may have to remove the corrector and give the inside a clean.

It's easy enough to do... just a bit fiddly.

I'd be happy to help if you wanted to meet up?

Ric · #3 18-12-2006, 05:52 PM

Thanks for the offer Matt, but I'm down the coast on holidays at the moment, so it's about a three hour drive. You may be able to help me though with a question about the removal of the corrector.

There are two allen key screws that hold the the corrector housing in place, once they are removed does that cast aluminium housing just lift off or is it on a thread. Also are there any glues which may also hold it in place.
Once that housing is off I should be able to carefully clean the inside of the corrector.

cheers

matt · #4 18-12-2006, 06:31 PM

Ric

You're describing an era of Celestron SCTs I'm not familair with.

With my 9.25 and with the current range of C8s all you have to do is remove the corrector retaining ring and then lift the corrector out from the front of the scope (gently) by holding the secondary housing.

On the current crop of Celestron's there are between 6 and 8 philips head screws which secure the corrector retaining ring.

The other important thing to do is make sure everything is returned exactly the same ie corrector position/orientation etc

Ric · #5 18-12-2006, 06:47 PM

Hi Matt, my original manual describes the same procedure. There are 8 allen head screws to remove and the corrector comes out, It also says to be careful of the orientation as well.
I was thinking about removing the housing so as not to change the orientation but the previous way actually seems to be the easier method.

Thanks for the advice

matt · #6 18-12-2006, 06:51 PM

It's just my feeling, but I wouldn't go removing the housing from the corrector.

I'd take the whole thing out in one piece. That way, you don't have to worry about both the orientation of the housing (and therefore secondary) and the corrector.

If you take the whole lot out holus bolus you only have one unit to worry about when it comes time to put it back in place.

Ric · #7 18-12-2006, 07:00 PM

Good point Matt, I shall definitely look into it a bit further before removing anything being a novice in this area.

cheers

astropolak (Joe) · #8 18-12-2006, 09:11 PM

On another note - what is the chance that the primary and secondary mirror needs to be cleaned up as well as the corrector lens? I would expect they will be just as bad as the corrector.

matt · #9 18-12-2006, 09:19 PM

Possibly...

but that's a whole different shooting match and so far Ric's only identified something on his corrector.

Worth a look though, once he gets the corrector off

Ric · #10 19-12-2006, 12:56 AM

Hi all, as far as I can tell it only affects the corrector. The mirrors look as if they are still in very good condition.

cheers

spacezebra (Petra) · #11 19-12-2006, 08:54 AM

This is quite interesting - I had no idea that fungus would get into the scope in that manner. Ric what do you put the milky appearance down to?

Ric · #12 19-12-2006, 09:12 AM

Hi Petra, it is a bit hard to tell exactly what it is but my best thought is that it is some type of fungus or mildew best described as a milky film, possibly caused by humidity. It has always been stored in its carry trunk but has been in coastal regions for the last 20 years.
From now on as well I think I will be keeping a couple of those little moisture absorbing bags in with the scope as well.

cheers

Ric · #13 20-12-2006, 11:39 AM

Hi all, I got stuck into the corrector last night and gave it a good clean. The patient came through with flying colours although the doctor needed a few rums afterwards. I worked through the manual and marked the orientation and there was no problem at all in the end.
The milky film washed off very easily in the end, it's hard to tell what it was and under a magnifying glass didn't show up much either. I suspect that it was some type of fungal growth, but it's all gone now and the corrector is crystal clean again. The primary and secondary mirrors were unaffected and still very clean so they were not touched.

Thanks Matt and everyone for all your help and suggestions, it's what makes this forum so great.

matt · #14 20-12-2006, 12:19 PM

Glad it turned out to be exactly what we thought, and you got it sorted Ric

Really happy you've had a success taking the corrector out and giving it a clean. Yes, the first time you do it your heart's in your mouth the whole time... but as long as you are methodical and take your time it's really not that bad.

Just not something you would want or should have to do too often. Only when necessary, as was the case with yours.

Well done, mate

Ric · #15 20-12-2006, 06:19 PM

Thanks Matt, with a bit of luck it should be right for another thirty years.

cheers