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Modifying infocus distance on a 114 short tube

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#1 Neinball

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Posted 24 June 2021 - 04:41 PM

Need a little help on something, I have a Meade 114 short tube, original draw tube came damaged so I replaced it with one from scopehed on eBay that does not have the built in Bird-Jones corrector/barlow, which is cemented in and not removable, During collimation I discovered that the lack of that element means the focuser needs about an extra inch of in-travel to come into focus. Anyone have any ideas on how to do that? Like if I could unscrew the eyepiece holder slot, flip it upside down and stick it inside the drawtube it would be at the perfect distance for focus, that's how close I am.

#2 photoracer18

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Posted 24 June 2021 - 04:58 PM

Stick a 1.5x-1.8x Barlow in it and it will raise the focal plane enough to focus. I don't know how corrected it would be however.



#3 ram812

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Posted 24 June 2021 - 07:02 PM

I know of someone that did this here on CN and the better solution on Bird-Jones conversions is to move the primary mirror cell forward the extra inch or so you need for that to work. A reduction of the diameter of the secondary wouldn't hurt as the factory ones are quite large. That's to get you to the magic 500mmf/l and not 1000😁. Hope this helps!

Good luck and CS, Ralph

#4 Neinball

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Posted 25 June 2021 - 11:24 AM

Stick a 1.5x-1.8x Barlow in it and it will raise the focal plane enough to focus. I don't know how corrected it would be however.


Tried that with multiple different barlows, shorties, full length, and screw ons, didn't work,

Edited by Neinball, 25 June 2021 - 11:24 AM.


#5 Neinball

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Posted 25 June 2021 - 11:29 AM

I know of someone that did this here on CN and the better solution on Bird-Jones conversions is to move the primary mirror cell forward the extra inch or so you need for that to work. A reduction of the diameter of the secondary wouldn't hurt as the factory ones are quite large. That's to get you to the magic 500mmf/l and not 1000😁. Hope this helps!

Good luck and CS, Ralph

Do you have a link to that thread by chance? We actually had to move the primary mirror a half inch backwards to get focus, it was too far forward.

#6 ram812

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Posted 25 June 2021 - 02:02 PM

Do you have a link to that thread by chance? We actually had to move the primary mirror a half inch backwards to get focus, it was too far forward.


Was that with the factory or aftermarket focus rack? Curious. The guy that did it is on CN still from time to time. I have to look back at my personal messenger conversations (PM) with him to get you the thread. Maybe hook you 2 up to come up with a solution! Never heard of having to move one back, though! He used his as a test-bed to see if he could do AP with a Bird-Jones type altered like yours. Be in touch.

CS, Ralph


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