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Tal Alcor 65 mirror problem

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#1 Finnstar69

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Posted 20 February 2021 - 11:50 AM

Hello to you all from snowy Finland!
Today i got my hands into a Tal Alcor 65 in good shape, or thats what i thought..upon inspecting i found that the mirror is missing about 10x10 mm piece from the outer rim. Pieces were still inside the tube. My question is: will this ruin the capabilities of this scope? Should i ignore this or fix it? If so, how? I could try to glue the pieces in place, would be it more of a worsening the situation than fixing it? Also one could cut a piece of a plastic adhesive mirror foil to cover the missing piece. What are your suggestions! Thanks!

Edited by Finnstar69, 20 February 2021 - 11:54 AM.


#2 mdowns

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Posted 20 February 2021 - 12:02 PM

Hello Finnstar and welcome to cloudynights. Could you post an picture of the damage? This would be really helpful for other members to see and comment.



#3 Finnstar69

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Posted 20 February 2021 - 12:24 PM

Here we go!

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#4 SpaceConqueror3

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Posted 20 February 2021 - 02:58 PM

My guess is perhaps a tiny bit as vast majority of the surface appears intact. I don't think that is repairable.  But the seller should be shot for not disclosing it before offloading on you as that's obviously the most critical component of the purchase.



#5 pbealo

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Posted 20 February 2021 - 03:10 PM

If you can't return it, you should consider painting the exposed glass black so you don't get odd reflections off of it. It should work OK after that.

Peter


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#6 catboat

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Posted 20 February 2021 - 04:34 PM

As Peter said above.  Don't try to repair it.  Just paint the chipped area black.  Your mirror will be a little "smaller", but that's what Alkors are all about.  Enjoy it. 


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#7 Finnstar69

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Posted 21 February 2021 - 02:02 AM

Thanks guys! Will do :) I dont think the seller had any idea of the condition of the mirror, as she was using the scope purely for decoration :) I drove over 400 km to get it (250 miles) thats whats **** me :( Dont you think one could use automotive adhesive mirror to fix the black spot? How about painting it with chrome paint? Just my thoughts..



#8 davidc135

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Posted 21 February 2021 - 04:27 AM

Trying to fix it would be far worse. It's not possible to replace the surface within around 1/20,000th mm and any reflected light would otherwise just degrade the image. 

Perhaps a replacement mirror could be found sometime.  David


Edited by davidc135, 21 February 2021 - 04:29 AM.

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#9 catboat

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Posted 21 February 2021 - 05:19 AM

Thanks guys! Will do smile.gif I dont think the seller had any idea of the condition of the mirror, as she was using the scope purely for decoration smile.gif I drove over 400 km to get it (250 miles) thats whats **** me frown.gifDont you think one could use automotive adhesive mirror to fix the black spot? How about painting it with chrome paint? Just my thoughts..

No, no, no!    sumo.gif   Repairs aren't possible.  Attempting repairs will make matters worse.  Black paint.  That's it.  Acrylic water-based hobby/craft paint should be fine.  Collimate and you're done.  The views will be good.

 

One thing you can do (after painting) is rotate the mirror in the cell so that one of the mirror retaining clips is placed over the damaged area.  Doing this will add a small undamaged area to the visible surface.   If you do this, you may need to place a small piece of sponge-like material between the damaged surface and the retaining clip -- something to fill the gap.  But use something soft and springy so the clip does not press on the surface.   Perhaps a piece of felt or one side of velcro.  A small gap is good -- about the thickness of a business card.


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#10 Finnstar69

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Posted 21 February 2021 - 07:04 AM

No, no, no!    sumo.gif   Repairs aren't possible.  Attempting repairs will make matters worse.  Black paint.  That's it.  Acrylic water-based hobby/craft paint should be fine.  Collimate and you're done.  The views will be good.

 

One thing you can do (after painting) is rotate the mirror in the cell so that one of the mirror retaining clips is placed over the damaged area.  Doing this will add a small undamaged area to the visible surface.   If you do this, you may need to place a small piece of sponge-like material between the damaged surface and the retaining clip -- something to fill the gap.  But use something soft and springy so the clip does not press on the surface.   Perhaps a piece of felt or one side of velcro.  A small gap is good -- about the thickness of a business card.

Great idea, many thanks!! Will keep my hobby-fingers away from "fixing" it :)


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#11 LukaszLu

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Posted 21 February 2021 - 07:23 AM

Hello Finnstar, I would try to forget about the problem and enjoy your scope. 10x10 mm makes only 3% of your mirror surface. I happened to drop the secondary mirror onto the 6'' mirror surface making similar damage, which made about 1% of the surface. It had absolutely no visible effect on the picture. I think that the psychological effect in this case might be much greater than the real damage to image quality.


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#12 Finnstar69

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Posted 21 February 2021 - 07:50 AM

Hello Finnstar, I would try to forget about the problem and enjoy your scope. 10x10 mm makes only 3% of your mirror surface. I happened to drop the secondary mirror onto the 6'' mirror surface making similar damage, which made about 1% of the surface. It had absolutely no visible effect on the picture. I think that the psychological effect in this case might be much greater than the real damage to image quality.

Most likely so smile.gif I will live with it.. Love the scope anyway. Piece of Soviet astronomical history with odd design. What is not to like lol.gif !


Edited by Finnstar69, 21 February 2021 - 07:51 AM.


#13 LukaszLu

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Posted 21 February 2021 - 03:49 PM

Piece of Soviet astronomical history with odd design.

The damage is a part of this history. Who knows what this telescope witnessed? You can even say that it gives the instrument a special character, emphasizing its uniqueness ;-)


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