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Help: mote of dust inside lens

equipment refractor
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#1 SkyDocLA

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Posted 01 August 2020 - 03:21 PM

Hi all,

 

I bought my first telescope used. It’s a celestron astroview eq 90mm refractor. When I bought it I saw some dust on the lens. So i took out the objective lens to clean it. However there is a speck of dust that is inside the lens. I can’t clean it off from either side. Like it’s buried in the middle of the lens. Very disappointed and feel like I wasted my money.  I have attached a picture. There is a small halo around the speck. Altogether it is about 2-3mm in diameter. 
 

how badly will this affect the performance? And if so, is there any thing I can do about it? Is it that it’s two lenses glued together and somehow a dust speck got sandwiched between the layers?

 

thanks for your help!

Attached Thumbnails

  • 9A7CF38A-7CDE-4C63-81EB-636934661C28.jpeg

Edited by SkyDocLA, 01 August 2020 - 03:22 PM.


#2 J A VOLK

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Posted 01 August 2020 - 03:45 PM

this speck will have no effect on performance - I would enjoy the scope and forget about it.  


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#3 sg6

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Posted 01 August 2020 - 03:48 PM

You will see/have no difference in performance.

Owing to the nature of the incoming light you could block big chunks of the lens with card and still have an image, Likely the noticable change would be brightenss.

 

The lens is not at the Object plane, so what is on the lens does almost nothing. And a speck of dust will do nothing. If you took a diamond ring and wrote your name on the surface then you might notice something. But only a might.

 

It is the odd nature of the incoming light and what is relevant - oddly not really the lens but the object and the object is several billion miles away.

 

Would say take the lens apart and clean. However that means you may not record the arrangemtent of the lens in the cell - amazingly it seems many do not. And you might get the speck off but in cleaning you create static and that attracks dust and fine hairs. Good chance you will have a speckless and clean lens but dust, fine hair and finger prints afterwards. It takes a lot to end up with a clean lens.



#4 TOMDEY

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Posted 01 August 2020 - 04:34 PM

It won't affect performance in the slightest. On the other hand, you can get a nice Spanner Wrench and pull it apart, if it's bothering you. Nothing like a good, clean lens! I'm always taking my lenses apart and never broke anything... yet...

 

Couple of my spanner wrenches here >>> Allows one to get a good grip on things.   Tom

Attached Thumbnails

  • 34 Cleaning the Dioptrx.jpg
  • 33 APM dedicated spanner 60.jpg


#5 SkyDocLA

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Posted 01 August 2020 - 05:30 PM

Thanks all for the replies! Feel much better thanks. It’s still day time but looking at terrestrial objects everything looks great! Spent most of the day oiling and greasing things, a few doamadads are rusty so have been cleaning and seems to be working. and am now trying to figure out the equatorial mount. 
 

I think I’m going to hold off pulling the lens apart for now so I don’t ruin it before I’ve even seen my first star! But just out of curiosity in the future, the lens pulls apart into two pieces? Is it glued or just held together in place? Also how does one get it out? Seemed to be wedged in there somehow? Does the spammer help remove it from the housing or actually just pulls the lens apart?



#6 KTAZ

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Posted 01 August 2020 - 05:38 PM

Some sandwiched lenses are, indeed, glued.

 

A spanner wrench "spans" across a retainer ring and sits in a small notch on each side of the ring so that you can unscrew it.

 

Don't mess with it at all. Clean it up and enjoy the scope. What you would inevitably discover is that all your effort to correct that little spot did nothing at all to improve performance. You'll just learn how to take something apart and re-assemble it.


Edited by KTAZ, 01 August 2020 - 05:38 PM.



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