Slight milky look to a new SCT corrector lens - concern?

[Gem]

Hi

There is a slight milky appearance to the corrector lens of my (new) C9.25 - it has been there since I bought it. It doesn't seem to be consistent across the lens.
Is this normal? Is it anything of concern? I have just emailed the shop but thought I would ask about for opinions...

Thanks :)

[MikeyB]

Not normal at all, in my experience of SCTs and Maks. Definitely a concern unless proven otherwise - if for no other reason than its resale value could be dramatically reduced.

If you possibly can, I'd suggest you get some experienced eyes to take a look and give you their opinion.

[casstony]

If it's on the outside it's possibly some thin deposit which could be cleaned off (with the dealers permission, or get the dealer to clean it if they're in driving distance).

If it's on the inside it could be a deposit from some sort of out-gassing from grease or from not letting the paint cure properly before assembly?

My C6 has a milky looking, uneven deposit on the inside of the corrector which I need to clean at some stage. Fortunately the whole front cell unscrews from the C6 so it's easy to get to the interior. In contrast the C11 is very clear looking.

[UniPol]

Well Grant, my new (end of last year purchase) C9.25" OTA exhibits the same thing. I never noticed it until collimating a few weeks ago when I shone a red light on the corrector plate to adjust the collimating screws. My first thoughts were "oh dear" what's this?, particlarly for a new scope. After a few moments, and looking at it more closely, I was convinced it is just very slack cleaning at the factory. I can see a very thin cloudy band around the secondary housing adjacent to the correcting plate and a larger area not far from it. It appears as if the cleaning cloth has been plonked on the plate and then a quick swirl around thus leaving the inner cloudiness and at the end of the swirl the cloth is lifted off leaving a further patch of cloudiness/smudging.

Having said that, the 9.25" performs brilliantly all the same and when I get around to it will clean the inner surface of the corrector plate properly, I've done them before and will do it again perhaps, just like the many chores around the house.

[PeterM]

"Dr Dons" jungle juice is a worth its weight in Naglers. Talk to Don at Bintel and he will set you right on the best way to clean your SCT optics (if at all necessary).

https://www.bintelshop.com.au/welcome.htm

As I'm sure you know, shining torches down SCT tubes is not recommended it usually causes you needless concern.

To ensure the inners of the SCT tube remain nice and dry and free from mould talk to Ron at Sirius Optics about the Far Point Dessicant Blocks for SCTs (yes, I declare I work there)

http://www.sirius-optics.com.au/farpoint.html

I clean my corrector every April 1st - yup April Fools Day, the day I also replace my smoke detector batteries and yes the corrector usually has heaps of crap on it from local fireplaces, dew (and I use a dew zapper) and who knows what and it comes up like new. You won't believe how incredibly filthy your corrector (or Newtonian mirror) can get before it starts to cause you issue.

PeterM.

[UniPol]

You're right Peter, where I live in the Blue Mountains has its drawbacks at times. Wood fires, apart from the smell and bronchial problems, definitely causes problems with the optics over a period (so much for living up here in the clean fresh air) and thought it was wonderful. I used to run a wood fire until natural gas became available but curse them now, somewhat analagous to a reformed christian or smoker. If you want to get a real shock, put your scope under a eucalypt/gum tree after a night's viewing and see what lands on your objective lens/corrector plate (especially if they are brand new) :mad2:.

[Gem]

You are confirming what I think. Scope performs ok but it needed better cleaning at the factory. Thanks! You make me feel better!!

Out of curiousity? where did you get your SCT from?

Thanks for all the posts. I will look into cleaning it some time. :)

[Gem]

Pete, do you clean the outside or inside each year??

[PeterM]

Outside only. I've had 4 SCTs over the last 6 years and never had need to clean inside one, and usage is typically 100 plus nights per year averaging 5 plus hours per night so a lot of use. Mind you they are housed in an observatory and aside from recently using dessicant blocks in an eyepiece plug I never cover the front of the corrector with its metal cover. Instead I drape an material type Aussie flag (any will do, bought from the $2 shops) over the corrector (not touching it) this keeps dust off and allows everything to breathe, remember its in an observatory but the idea is the same if can be left safely that way, also bets way for Newtonians let them dry out don't lock it in with end caps.
We have had a Meade and a Celestron SCT in the shop with very obvious and significant mould on the inside of the corrector and have rectified these and not seen any obvious resulting damage. These were really extreme and I would talk with whoever you bought from before undertaking to remove a corrector.
Don't panic, oh and don't spray, tip etc any cleaning liquids onto the corrector when cleaning, it's too easy for it to run and will find its way down the sides of the corrector and almost certainly onto the black paint inside tube leaving white streaks in the paint ( I did it years ago). You will need Dons cleaner (Bintel) & Blower brush, Lens tissue, Microfibre polishing cloth, Orion have these in packs (we stock them at Sirius) and there are lots of articles on how to clean successfully on this site and by Googling.

[UniPol]

I bought from the US.