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Lunt 50PT Ha o-rings / pressure tuning

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I recently bought a 2nd hand Lunt 50PT Ha (on a different platform).  The vendor said he had only used it a handful of times since buying it and it shipped in the original box.  It seems fine, focuses well (although I find the helical focuser a bit of a pain compared to crayfords).  But it doesn't show any Ha features on the surface of the Sun!

Long story short, I completely opened up the pressure tuner and found a bizarre thing.  Its well greased, there's no detritus (and it doesn't lose pressure).  But there was only one O-ring in it?!  The tuner itself has grooves for two o-rings and the video on Lunt's website (on how to replace o-rings) shows a tuner with two o-rings when it comes out.  And they ship replacements in batches of two.

So I'm guessing that somehow the original scope shipped with only one o-ring fitted? (It wouldn't make sense for the vendor to have removed one?).

I'm hoping that's what it is, b/c then the inability to resolve Ha features may just be insufficient pressure building up?  In which case, does anyone know where I can get these replacement o-rings please (Lunt's US website has them but that's only for shipping to the US)?

If it's not that, and the scope is only meant to have one o-ring, any ideas on the problem?  The ring & tuner seem well greased.

Thank you!


(EDIT: in the meantime, the next time the sun comes out, I'm going to try moving the current o-ring from the higher groove to the lower groove in case that longer distance from the base is why the pressure isn't building up sufficiently?)

Edited by vineyard

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Some of these scopes did indeed ship with only on O ring, you can get spares from Bresser either direct or through Telescope House.



Edited by Davey-T
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Wow, how did they let that happen; doesn't bode well for product control?  Anyway, thanks Dave - I'd tried looking on their website and it's not listed, but will try calling directly!  (I'll also look in my local hardware store - no doubt it'll be a bespoke thickness just because...)  Cheers, Vin

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Thanks Davey-T & johninderby.  I eventually contacted Lunt directly, and Bresser Europe in Germany are sending some o-rings :) (FLO also recommended speaking to Bresser).

Btw, while talking to Faye at Lunt she explained that the 50THa ships with 1 o-ring only deliberately.  They found that if there were two o-rings, re-threading the tuner on required too much force.  So it is now deliberate that the first (lower) groove is empty, and the o-ring is in the second (higher) groove.

Anyway, happily after re-greasing, taking the tuner off completely to equalise and then slowly threading back (and, ahem, putting a black t-shirt over my head) I managed to see some Ha features this morning :)



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Glad things are working out for you now Vin.

I found a way to attach a second o-ring to the LS50 and wrote a brief report on SGL about it 2/3 years ago. It involved loosening the end screw on the piston which made it slightly easier to screw it onto the brass housing. But sounds like you don’t need any further tinkering. Enjoy - it’s a great little ‘scope.

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Glad you saw some detail- just wait til the sun gets more active and it will be truly wonderful!  I luv my double stacked LS50 :)

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