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Can you help ID a thread size

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#1 dcaponeii

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Posted 23 February 2021 - 08:06 AM

On the visual back of the 12” ACF Meade uses a “standard” thread for their eyepiece adapter. This is a male thread onto which the eyepiece adapter or their 0.63 reducer/corrector threads onto. Does anyone know this thread size? I need an adapter to mount my Optec 0.62 reducer. The threads on the Optec reducer are smaller diameter than the visual back on the Meade. Thanks for any help you can provide. I figured I could just get a 2” eyepiece adapter and be done with it but noooooioo! Life is never that easy.

#2 ayryq

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Posted 23 February 2021 - 08:15 AM

Check this site:

https://agenaastro.c...-explained.html


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#3 jeffreym

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Posted 23 February 2021 - 08:16 AM

This should be standard SCT thread.

https://agenaastro.c...-explained.html

Have fun,

Jeff


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#4 dcaponeii

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Posted 23 February 2021 - 08:46 AM

This should be standard SCT thread.

https://agenaastro.c...-explained.html

Have fun,

Jeff

Helpful link.  But even Agena Astro only seems to stock an adapter that results in the slip fit 2" connection.  I need a 2" male thread not a slip fit.  Without adding excessive length or I run the risk of not reaching focus.  The crux of the problem is that my older JMI Crayford focuser using the same 2" SCT thread which is too large to thread the Optec reducer onto.  The 2" Meade Eyepiece adapter was the obvious solution but when I tried to order one the order confirmation came back as being on back order until AUGUST 2021.  Now it's gone from their website entirely.  UGH this has been frustrating on top of all the crappy weather we've been having since the reducer arrived (no causal connection I'm sure).



#5 barnold84

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Posted 23 February 2021 - 02:06 PM

Helpful link.  But even Agena Astro only seems to stock an adapter that results in the slip fit 2" connection.  I need a 2" male thread not a slip fit.  Without adding excessive length or I run the risk of not reaching focus.  The crux of the problem is that my older JMI Crayford focuser using the same 2" SCT thread which is too large to thread the Optec reducer onto.  The 2" Meade Eyepiece adapter was the obvious solution but when I tried to order one the order confirmation came back as being on back order until AUGUST 2021.  Now it's gone from their website entirely.  UGH this has been frustrating on top of all the crappy weather we've been having since the reducer arrived (no causal connection I'm sure).

Hi,

 

I assume that the 12" ACF has the standard Meade/Celestron 2" SC thread. I'm not certain how applicable my setup is to yours but I would guess it should fit:

I am using an additional focuser at the back of my 8" ACF. It threads directly to the tube and has a length (if fully retracted) of about 110mm. I used a Meade reducer (with flattener lens removed) and could easily reach back focus. To attach the reducer, I bought a 2" "barrel" (please correct me on how this is actually called, as I'm not a native English speaker) to SC thread adapter. The rest is standard and I can focus although I had to turn the focus nob on the tube for a while.

 

Btw, I'm changing the modded Meade reducer for an AstroPhysics reducer which is said to be compatible with coma free optics. Its working distance is 85 instead of 105 mm. I don't want to use the Optec as it's more expensive than the AP and I also need an additional adapter to connect the Optec to any other thread.

 

Given that, I would think that you should also be able to reach back focus, despite the higher focal length of your 12" scope.

 

Björn


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#6 jeffreym

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Posted 23 February 2021 - 02:07 PM

Helpful link.  But even Agena Astro only seems to stock an adapter that results in the slip fit 2" connection.  I need a 2" male thread not a slip fit.  Without adding excessive length or I run the risk of not reaching focus.  The crux of the problem is that my older JMI Crayford focuser using the same 2" SCT thread which is too large to thread the Optec reducer onto.  The 2" Meade Eyepiece adapter was the obvious solution but when I tried to order one the order confirmation came back as being on back order until AUGUST 2021.  Now it's gone from their website entirely.  UGH this has been frustrating on top of all the crappy weather we've been having since the reducer arrived (no causal connection I'm sure).

Okay, so are you saying you need to go from male SCT threads (2"-24) to some other 2" thread?  M48? Those would be common adapters.

https://agenaastro.c...apter-c-04.html

Am I missing something?

Jeff



#7 dcaponeii

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Posted 23 February 2021 - 02:12 PM

Okay, so are you saying you need to go from male SCT threads (2"-24) to some other 2" thread?  M48? Those would be common adapters.

https://agenaastro.c...apter-c-04.html

Am I missing something?

Jeff

Turns out I was completely wrong in my approach to the problem.  Apparently the Optec reducer is a friction fit into the Crayford focuser.  The female threads I was "assuming" should thread onto my Meade visual back are actually for 2" filters.  I've got to get back to the observatory and rethink the JMI NGF-S focuser (yes it's OLD!).  It currently has a tube in it with the same thread as my Meade visual back.  I think this tube gets removed and then the Optec reducer is inserted in its place.  Not at the house and photos of the old NGF-S focuser are hard to come by on the web.  I've yet to find a picture of one that has the threaded tube.  But talking to the folks at OPTEC (Thanks Jeff, not sure if it's this Jeff) I think I'm on the right track.



#8 dcaponeii

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Posted 23 February 2021 - 09:30 PM

Success!!  All I had to do was remove the SCT threaded adapter and then the Optec 0.62 reducer and the backfocus spacer slipped right in.

9E1145F4-67CE-49E6-B7A9-D6139E180FF3.jpeg



#9 dcaponeii

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Posted 25 February 2021 - 08:20 AM

Hi,

 

I assume that the 12" ACF has the standard Meade/Celestron 2" SC thread. I'm not certain how applicable my setup is to yours but I would guess it should fit:

I am using an additional focuser at the back of my 8" ACF. It threads directly to the tube and has a length (if fully retracted) of about 110mm. I used a Meade reducer (with flattener lens removed) and could easily reach back focus. To attach the reducer, I bought a 2" "barrel" (please correct me on how this is actually called, as I'm not a native English speaker) to SC thread adapter. The rest is standard and I can focus although I had to turn the focus nob on the tube for a while.

 

Btw, I'm changing the modded Meade reducer for an AstroPhysics reducer which is said to be compatible with coma free optics. Its working distance is 85 instead of 105 mm. I don't want to use the Optec as it's more expensive than the AP and I also need an additional adapter to connect the Optec to any other thread.

 

Given that, I would think that you should also be able to reach back focus, despite the higher focal length of your 12" scope.

 

Björn

Failure to reach focus with the installation using my JMI Focuser.  Looks like I need about another 1/4".  I'll have to remove the JMI and try again, as soon as my adapters arrive.  This is becoming much more of a chore than I had hoped for.  



#10 barnold84

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Posted 25 February 2021 - 08:28 AM

Failure to reach focus with the installation using my JMI Focuser.  Looks like I need about another 1/4".  I'll have to remove the JMI and try again, as soon as my adapters arrive.  This is becoming much more of a chore than I had hoped for.  

I'm a bit surprised as the SCTs usually have a very long back focus range through the focuser/movable mirror.



#11 dcaponeii

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Posted 25 February 2021 - 10:22 AM

I'm a bit surprised as the SCTs usually have a very long back focus range through the focuser/movable mirror.

Someone in another post said their LX600 focus knob got stiff as you approached the most forward position of the mirror.  It's possible mine is the same way although I definitely hit a physical stop.  It was stiff for the last 1/4 turn of the coarse focus knob.  Hard to know but in any case I can't get there with the current scope and it's all working great otherwise.  Given the physical stop I believe that the scope is functioning properly.  The physical size of the old JMI NGF-S focuser is deeper than more modern focusers.  I'll try it with fixed spacers on the visual back and then see where to go from there.  It's only money!! UGH




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