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Replacement Objective Lens


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Hello,

I was wondering if anyone could advise me on where I could get a replacement objective lens for my 120mm refractor?

Any help in this matter would be gratefully appreciated.

Thanks.

Oh yea, its a dark star alpha 120 achro refractor (identical to helios)

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Even if you were to find a cheap enough replacement objective you would still need to collimate it once installed, so a new scope is probably the best option.

Out of interest, what happened to your existing objective lens?

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Well im not sure why its done it but my existing lens has gone all cloudy, i havnt used any cleaning fuid on it or tried to clean it with anything harsh, its almost like its steamed up, yet if i get some cotton wool and warm water, it makes no difference at all, almost like the problem is internal. Any suggestions other than replacement would be great, i dont know enough to be taking it all part, other than unscrewing the lens from the scope.

TA

p.s. I have tried leaving it in a warm place and cold place for a while and that made no difference either, so i put it down to the lens itself being worn?

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Sounds like moisture has got between the elements of the doublet.

You did the right thing leaving it in a warm place (ordinary room temperature ought to be enough). If you didn't already, make sure all lens caps are off and no eyepiece is in place, so that air can circulate round the lens.

You say you tried cleaning - did you put water directly onto the lens? It could have crept inside.

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Thanks for the replies, i have had all the caps off now since last night and theres no improvement, i will keep them off as long as it stays in the house and hope for an improvement. If its moisture between the elements then will it help if i hairdryer it on a cool setting? I know it would take a while but if its worth a go then i will try.

I did try cleaning with water yes, but that was after i noticed the cloudyness, i only used very lightly dampened cotton wool though.

Thanks

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If it is moisture between the lens I suspect that it has reacted with the glass adhesive. Odd that it has reacted with it as I would have expected it to have been chosen not to as a scope will experience temperature change and so possible ingress of moisture.

If nothing works, and I suspect that you want a permanent solution, then the lens may need a fairly extensive repair. As in separating, rebonding and possibly after that recoated.

I enquired about a lens repair last year and the best (most helpful) I could find was Kingsview Optical, based at Rye.

If all else fails it may be worth an email to them stating the problem and asking for an idea of the cost. Don't ask for a quote as all you want at this time is a rough idea, and a quote would mean sending the lens and paying postage.

I have not taken my lens down, I wanted to visit them, so in honesty this is only from the reponse's they gave, which was prompt, useful and helpful.

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I think the lens is an air-spaced doublet so there would be no cement to be affected. You could try removing the lens from the cell and carefully separating the 2 lens elements marking their edges so that you can keep their orientation to each other and don't loose the foil spacers - you you may be able to clean the inside lens faces then - I guess it could even be mould - that has been known on older scopes. Use distilled water and very gentle swabbing with 100% cotton wool in a motion that goes from the centre outwards. Replace the cotton wool after each swab motion.

John

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Thanks for all your advice guys, I popped the scope into a warmer room overnight and then replaced the cap with a small silica gel bag this morning. I have just checked it and its pretty much clear as day now, there a little cloudyness left but i think thats on the outside so i should be able to sort that now easily enough.

Once again thanks for all your advice, had i not have enquired then i may well have been the proud owner of a new scope by now (not that that's a bad thing :rolleyes: )

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