William Optics 10-1 SCT Crayford focuser on 12" LX200 question

[Omaroo]

Hi all! I've just bought Houghy's William Optics 10-1 Crayford focusser for SCT and am wondering if someone can tell me if I'm missing something on the scope that is meant to be there. I believe that these things are called "Visual Backs" but I'm net certain.

My 12" LX200 came with a Peterson Engineering EyeOpener which mounted the Meade Zero Shift Microfocusser - both of which I've removed to reveal a 3 1/4" (83mm) -odd threaded section at the back.

My question is this: How do I connect the W/O unit to this thread when it only presents a 2" female threaded section? Am I missing a pice of telescope that comes with a new unit, or do I have to buy an adapter to up-size the focusser's threaded section to suit that of the scope? I'd love to use this focusser as I'm not a fan of the Microfocusser, and the 10:1's feel will deliver far better focussing results. Too many adapters though and the unit won't be able to swing through the forks either....... :(

Thanks in advance
Chris

[h0ughy]

that black ring part at the back of the focuser can screw off, when it is off will that fit your peterson thread?

[Omaroo]

Alas, no David :( It reveals another 2" thread. I presume that the the black ring is no more than a 1/2" extension or balance ring.

[h0ughy]

sorry:shrug:

[beren]

This is the original visual back of my LX200gps, which when taken off reveals what you depict in your first image

[Omaroo]

Thanks for that Beren. That looks more sensible.... and looks like what I have to get hold of.

Could I ask what size the threaded barrel is on that unit?

[Merlin66]

I think the issue is that the rear thread is larger on the 12" than on the smaller models. I've just removed the micro focusser and fitted the Lumicon Giant Easy Guider which screwed directly on the the rear threads.

[Omaroo]

So the stepped-down standard Visual Back gives you 2" or greater? I take it that it does step down smaller than the 3 1/4" you get straight off the back.....:shrug:

[beren]

Ouside diameter 2inch, inside 1 1/2 inch

[Merlin66]

Never thought about it until now, but the usual SCT thread must have been on a 3 1/4" threaded adaptor to fit the back of the telescope!
Not at home so can't check it out. I know that the easy guider gives a much more open view similar to the "eye opener"
Will the focusser fit the standard SCT male thread? which is around 50mm.

[Don Pensack]

All larger SCTs have a 3-1/4" thread (diferent for Meade and Celestron) on the back to which a 3.25" to SCT male thread adapter is threaded. The I.D. of this adapter reduces the illuminated field so AstroPhysics, Peterson, Lumicon, and others have made adapters that thread onto the 3.25" thread and accept a 2" tube from a diagonal (for the minimum vignetting possible).
The WO Crayford focuser and the Meade ZIS focuser attach to the normal male SCT thread (50mm), so the original step-down adapter has to be used to accomplish the mounting of either focuser or any other visual back accessory like a focal reducer.
Lumicon and others make photo accessories that thread directly to the 3-1/4" threads, but WO does not.
The I.D.of the visual back adapter is a smaller I.D. than 2", but c'est la vie.