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Celestron 102 SLT main lens seems to have fingerprints inside

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#1 HughO

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Posted 08 July 2020 - 03:59 AM

I've just bought a second hand Celestron 102 SLT, unfortunately when I try a selection of different eye pieces in it I get very wavy results. I've tried the same lens in a Celestron 70 travel scope and the a pin sharp.

 

When looking at the front there is a nasty smear and some finger prints, I've tried to clean these off but the seem to be on the inside.

 

So then i spent some time trying to see if there as any instructions on how to take this apart to clean the inside, or a diagram etc. Without luck.

 

I decided to see what came apart easily, and the dew shield screwed right off, and revealed these screws.  I'm looking for guidance as to how to proceed.  Or what are the risks with proceeding.  I'm assuming that if I unscrew these I should be able to take this apart and clean the lens.  And fingers crossed be able to put it all back together again.

 

Has anyone done this before, or know the process or where I can find diagrams before I plunge in?

 

 

 

 

 

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#2 HughO

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Posted 08 July 2020 - 05:33 AM

Ok this turned out to be a very easy job, but the telescope still isn't performing. Getting a far clearer image from the (borrowed) Celestron 70 travel.

 

Is it possible to get new lenses for this kind of scope?



#3 doublevodka

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Posted 08 July 2020 - 05:48 AM

May be worth a look at this thread? https://www.cloudyni...sability-hacks/

 

May not be the same problem, but somewhere to start at least :)


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#4 sg6

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Posted 08 July 2020 - 05:51 AM

Assuming you managed to separate the 2 lens and so clean the internal surfaces. I would start to suspect someone else managed to take ot apart and oput them there, and from the poor performance they may have 1 lens the wrong way round.

 

Would mean you have to repeat the process and write down the high and low faces of the 2 lens and then find out if the orientations are correct (sensible).

 

The lens are very likely a Fraunhoffer arrangement - think +ve lens at the front and the higher domed face to the sky. Hard to easily describe as the more domed face is also the lesser radaii, and it can confuse.

 

The rear lens would be orientated such that the face most matching the rear of the front lens is in closest (almost) contact. Pretty obvious.

 

If done incorrectly I would be guessing the front one is wrong as people generally put the flatter face at the front. Then the radaii mean the rear lens very likely has to be wrong so they do not contact each other.

 

So afraid you may have to repeat the process again. Just before hand earch out achro doublet lens arrangements so that you can check the probable orientation.


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#5 HughO

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Posted 08 July 2020 - 06:14 AM

Thanks guys.  

 

At sg5 I will give this a go.  It's also hard to describe the issue i'm having.  Right now I'm looking at flowers in the back garden, with the travel scope it's all sharp from the center all the way out to the edge even when i move my eye around or try to focus on different parts of the view.

 

With the nexstar it seems to be foggy when moving away from the center,  also when i try to focus on a different part of the view, then it seems to become a bit like a kaleidoscope as i move focus. (if that makes sense.)



#6 HughO

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Posted 08 July 2020 - 06:36 AM

@sg6 you legend!  I honestly didn't think that would work, but I flipped the front lens and it's a completely different telescope. 


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