cleaning the INSIDE of a SCT objective lens??

Posted by Anonymous

on Mon, Sep 22 2003 3:41 AM

Hi all,

Got a 10'' SCT Meade that is about 10 years old. It's been sitting in a big plastic box most of the time, stored well.

Been breaking it out a bit lately, and I noticed some tiny white "cobweb" looking mold or something in places on the objective lens, but definately on the INSIDE. I figure anything stored that long is bound to grow something I guess, so I'm not freaked out.

However, if I were to start taking screws out of the front of the tube, can that objective be removed and cleaned with any hope of putting it back together? What happens to the secondary....is this something better not messed with? Should I take it to a dealer for a professional cleaning?

The scope is far from being unusable as is. Just thought I'd get a opinion or two.

Thanks in advance,
JC

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Posted by chipdatajeffB

on Mon, Sep 22 2003 3:47 AM

JC:

Conventional wisdom says not to clean it unless you're having trouble seeing through it. That goes for just about any kind of scope or optics.

Since the corrector plate not only is a lens but also holds the secondary, if you DO clean it you will need to recollimate it. I'd suggest taking it to a dealer if there is one nearby. Otherwise, contact Meade about it.

They might have a "tuneup" special that includes other tweaks, as well.

Wink [;)]

The universe is not only stranger than we imagine, it's stranger than we CAN imagine. --- JBS Haldane

Come visit me at Comanche Springs Astronomy Campus (we're on Google Maps) in Texas.

www.3rf.org

Posted by jballauer

on Mon, Sep 22 2003 5:33 PM

First, let me say that I would recommend against doing this unless you know the views are being hindered.

Second, I did this myself just the other day because I needed to clean the secondary (I'm also to the point with my 10" LX200 where I'll do just about anything to improve its performance).

Removing the front ring will allow the entire corrector plate and secondary to come off in one piece. When you do it, make sure the scope is tilted up slightly so that it doesn't crash to the ground. Remove the retaining ring. Mark the exactly location on the mirror against the tube so that you can replace the plate EXACTLY the way you found it. Remove the corrector plate being careful not to remove any of the cork shims with it. Then, do your business to the plate and/or secondary.

Replace the plate back the way you found it and replace the retaining ring, being careful not to tighten it TOO tight.

Check your collimation...it will be a little off, but not a whole lot if you properly replaced the plate the way you found it. I got lucky with mine and my collimation was dead-solid perfect.

Give it a try if you want with the understanding that you reap what you sow; however, sometimes with older scopes it's good to do stuff like this so that we learn about how our scopes work. Getting rid of some of the fear factor can allow us to make substantial mods in a way that can improve the system.

jay
www.allaboutastro.com