Recentering sweet spot possible?

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Recentering sweet spot possible?

Post by Gingerfish »

I really never noticed that the sweetspot was off in my lunt 50. But after modding it, it became quite apparent that it was not in the middle! Is there any way to recenter it? I will be barlowing my mod to "zoom" in on the sweetspot, so having it centered would make life easier.

I found someone on CN who did this with a Lunt 60 by adjusted the focuser, but of course that is not really possible with the crappy helical focuser on the 50 (a FeatherTouch is next on the list of things to buy).

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Re: Recentering sweet spot possible?

Post by Gingerfish »

Thanks!

Let me guess, it does not come out of the factory scratched like this? :?

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Re: Recentering sweet spot possible?

Post by AndiesHandyHandies »

Hi

I used a tilter in front of my PST Etalon and used auto-collimation from the front on the bare etalon on a refractor to set the etalon at 90 degrees to the optical axis.

I punched a hole near the edge of an old greetings card and drew a 1/4" black cross from it. Stand 20' infront of the telescope objective with the cross facing and centre the reflection from the front of the etalon looking through the hole. Move your head from side to side and up and down to centre the vignetting.

Improved the view.

Tried on my Maksutov but not as easy. Taken the tilter off.

Cheers. Andrew.


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Thanks guys,

Yes, it was bought used. And yes, I know he tried to mod it, although just a "stage 1" mod according to himself :cry:


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Oh btw, if I push it too far, is there anyway to get it back out again? I see I can unscrew the black ring - if its not too damaged at the bottom thanks to the previous owner.


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Excellent! Will have a go when ever the rain stops again...


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Re: Recentering sweet spot possible?

Post by Gingerfish »

I just noticed that Oliver at Beloptik has the LS50 under his repair service. I might ask him to do a service on it - just in case! I can see that the retainer ring has been unscrewed as well, so God only knows what has been done inside!


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Re: Recentering sweet spot possible?

Post by marktownley »

I don't think you'll achieve anything sending to Beloptik, there's nothing inside that can have anything done to it. I have the same my my LS50 with the sweet spot, the problem is the etalon cell is larger than the etalon, if I gently rock mine side to side I can hear the etalon moving in the cell. I did have the idea to use some small pieces of (electrical) tap around the periphery to take up the slop but have never got round to doing it


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Ah ok ;) I'll have a look at it then, and see what can be done


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Re: Recentering sweet spot possible?

Post by Gingerfish »

I just can't seem to get a break! Went out to do some proms imaging, Focused, started imaging and went to get some coffee. Came back 5 minutes later to a off band sun. So there is definitely a leak somewhere, and I I don't think it's from the PT, as I have two new o rings in there. I guess it has to go back to Lunt themselves now, as there is no service in the UK I presume? :roll:

Lesson learned I guess, don't buy a used solar scope! :cry:


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Re: Recentering sweet spot possible?

Post by marktownley »

Theres not many places it can be leaking from - have you checked the allen stud on the end of the PT knob?


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Yes, I went over everything. Even regreased the o rings again. Same problem. Lunt wants $150 to fix it, which isn't shocking. But it's still going to hurt when you add in shipping and duty :cry:

Still, cheaper than a new scope I guess...


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Re: Recentering sweet spot possible?

Post by marktownley »

It can only be on either the o-rings, seals around front and back collimating lenses or the stud.

Sounds extreme, but you might want to pressurize the module up and briefly immerse it in a bucket of water - like you would with a bicycle inner tube to look for a puncture. It won't be in there for long - maybe 10 seconds while you look for the bubbles. It's a pressure vessel so it has in effect some waterproofing by definition. Just don't leave it in! Like I say, i'm talking seconds here to find the bubble train...


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Smart! Bubbles are coming from the front end :(


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Re: Recentering sweet spot possible?

Post by marktownley »

PTFE tape? Re-seat the front threaded section?


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Right, I will have to take it apart then :o Surprisingly, Lunt doesn't even mind! They just told me if I damage it, it will cost me more to fix.
I was told there was silicone inside, but does anyone know what kind? I presume it will be gasket sealant or something similar that can take pressure, and doesn't shrink or harden?


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Re: Recentering sweet spot possible?

Post by Gingerfish »

Cheers! Well I am more relaxed about the whole thing now that Lunt gave the OK. I just need to order a pin wrench, the one I had was too thick. Looks like I need a 2mm.

Btw, this first lens, is that one of the collimation lenses I see in the drawings? Anything I should worry about here?

I have one of these, would that do for sealing it back up?

https://www.amazon.co.uk/gp/product/B00 ... UTF8&psc=1


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Re: Recentering sweet spot possible?

Post by Gingerfish »

I don't know if it is vapor free or not. I will send Oliver an email


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Re: Recentering sweet spot possible?

Post by Gingerfish »

In the meantime, I took of the retainer ring. And yeah, the seal has most definitely been broken! But WHY would you be in here?! To remove dust?

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Re: Recentering sweet spot possible?

Post by Gingerfish »

Finally received the silicone on Saturday, and got it pressure tested today. All good! No leaks. Now I just need some sun! :D


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