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Focus problems

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#1 gspith



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Posted 16 May 2008 - 09:19 AM


I am not that new in astronomy but also not that experienced. I have a Lightbridge 12'' for over a year now and I am still not fully happy.
The collimation problems I faced at the beginning were solved by replacing all knobs (both primary and secondary mirrors) and primary springs with those sold by Bob'sKnobs.

Regading focus, I had to buy an extender and still sometimes I have to place the eyepiece halfway into the focuser in order to achieve focus.

Has someone had the same problem?

Does someone know a way to calculate the minimum focus distance of a telescope? I am asking this because I have also tried to focus on terrestrial targets with no result.



#2 ckkrish



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Posted 28 June 2008 - 07:34 AM

Hi George,

I have the same problem, but to a lesser degree.  Just last night I found that I need to use the extender tube to get focus on the 26mm eyepiece that came with the telescope. This was the first use after I changed the collimation bobs and springs and did a complete re-collimation.

Sorry, I don't have answers to your focus distance question. If you have gained more insights into the situation, kindly post to the forum.


#3 provencial


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Posted 04 July 2008 - 02:46 PM

You may want to try using a star diagonal to help achive focus, they are fairly inexpensive and help put the eyepeice in a more comfortable viewing postion.

good luck!

#4 steelken



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Posted 24 April 2009 - 09:22 AM

Hi I had the same collminating problems and also changed to Rob's  equipment. I also had to centre the main mirror !  1  to do this cut a circle out of ridgid cardboard the same inside diameter of the upper tube,  2 mark the center  and at 6 inch radius make 3    1/4 inch holes at 120 degree intervals . place this in the top tube above the spider. look through the eypiece holder and have someone adjust the main mirror until you can see half of all 3 holes. Now your main mirror is centered and you can perform  your cllmination.
regards Ken

#5 hamdul


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Posted 25 April 2009 - 10:16 AM

Have you ever used a star diagonal on a reflecting scope?  I didn't think it was possible unless you were triple jointed in the facial area

#6 Mark Sibole

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Posted 17 May 2012 - 03:38 AM

I have no expierance of the Lightbridge scopes so im taking a shot in the dark at it.
Try an extension tube to get the needed distance.
Aslo make sure it is assembled correctly as the distance from the main mirror to the secondary is critical for focus.
There are times where I wish I had access to every product to familarise myself with it to help out more.
All I can do is download users manuals and go from there on most things.
Mark Sibole
MTSO Observatory
Fife Lake, Mi.


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