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Diagonal trouble with Jason 311

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#1 jkd


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Posted 19 January 2021 - 09:20 PM

Hi there,

I've been getting my wife's old Jason 311 telescope working, with new pieces of equipment replacing eyepieces etc. that I lost the originals for.  I'm a beginner at this and mainly wanted to be able to share seeing some events with my kids that they were excited about.

I got some parts that work together for direct viewing, but I'd really like to get a diagonal working to make it more comfortable.  I've got the original .965" diagonal, but each configuration I try it in, I can't pull the focuser tube in far enough to get a clear view.

I'm just trying to view the moon, and I can get a clear direct view without the diagonal.  I like the idea of getting new use out of a childhood telescope, so I was hoping to make the Jason work.  At the same time, I wanted to try and spend money only on new 1.25" parts rather than .965" parts, so they'd be useful for other telescopes. 

Can someone suggest what I might try next?

Here's the parts and configurations I've tried:

EP=Svbony 23mm 1.25"
AD=Astromania .965" to 1.25" adapter
DG=Original Jason .965" diagonal
FT=Focuser tube .965"
BL=1.5x lens element from Svbony 2x Barlow Lens 1.25"

EP-AD-DG-FT - Can't move focuser inward far enough to focus

EP-BL-AD-DG-FT - Same, can't move focuser inward far enough, BL didn't make a difference

Should I try a 1.25" diagonal instead?  It sounded like that might make the inward travel problem worse.

Or should I get a diagonal adapter to replace both parts and shorten the path that way?

Any help is greatly appreciated!


#2 ryanr256



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Posted 19 January 2021 - 11:44 PM

I have a 311 and was unable to achieve focus with any combination of 1.25 adapter/diagonal/hybrid diagonal/etc.

So, I am keeping the 0.965 diagonal and have begun acquiring decent to high quality 0.965 eyepieces.

My decent set is the Meade MA eyepieces, still working on tbe high quality ones.


#3 Jon Isaacs

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Posted 20 January 2021 - 12:22 AM



Hello and :welcome: to Cloud Nights.


If you are running out of inward focuser travel, you maybe out of luck in terms of using 1.25 inch eyepieces.  1.25 inch diagonals require more inward focuser travel. 


Part of the problem is that the 1.25 adapters use up space.


You best be is what is called a hybrid diagonal, it has a 0.965 inch nose piece but takes 1.25 inch eyepieces. 


A good resource for inexpensive parts is Bill Vorce at the Telescope-warehouse.  He has a Hybrid diagonal for $11.




Bill also carries entry level 0.965 inch eyepieces.  




I like Bill, he's a straight shooter.  He often has stuff not listen.  Just send him an Email or Cloudy Nights PM and ask him if you want something you don't see.




AgenaAstro also has Hybrid Diagonals.





#4 MJB87



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Posted 20 January 2021 - 07:01 AM

Moving this too Classics for a better fit...

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#5 wrnchhead



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Posted 20 January 2021 - 07:36 PM

I can't remember the exact model of Jason I had ( I swear it was a 313) but it had an adjustable drawtube, you loosened a set screw and could make a large adjustment, then used the focusing tube to make the fine tuned adjustments. 


Looked at the manual (it's available at https://wiki.telesco...tor_Manual.pdf)

and yeah, it should be able to be adjusted, assuming you may not have tried it. Do you have any photos?

#6 jkd


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Posted 20 February 2021 - 10:55 PM

wrnchhead, thanks for the suggestion and the link to your Jason's manual.  Figure 4 on page 7 looks almost exactly like my 311 - except for the 311 doesn't have that outer draw tube and set screw!  frown.gif  That would have been a good feature at this moment.


Jon, thanks for the advice, I'll look through Telescope Warehouse's stuff.


Bob, thanks for pointing me in the right direction (or away from the wrong direction)!  It's good to be able to contact someone with exactly the same product, who's already tried things out.


I might try one of the .965 Meade eyepieces at Telescope Warehouse.


Thanks again!


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