Which Barrel extension?

[Commanderfish]

Hi there,

 

I have an Explore Scientific ED127.  The focusser takes 2" eyepieces.  It has two screw-in barrel extensions, each of which extend by 37mm.  I've determined that for my range of eyepieces, it would be perfect to have one barrel extension of about 50mm.  

The only trouble is that when searching, there seem to be a plethora of different widths/fitments.  Which one do I need?  I know it's not the T or T2 type fitment.  Is the kind I want called M48?  It has to be threaded so it will screw in to the focusser (about 5mm of thread).  It also needs to have a female thread at the eyepiece end to accept filters.  Finally, it would be great if it had a compression ring clamp on it - though that is not necessary as I already have a seperate one (if I can manage to unscrew it from my existing extension!

 

Any advice appreciated! 

[rockystar]

Have a look here: http://www.altairastro.com/self-centering-extensions-adapters/

I have the 50mm extension and 2"->1.25" adaptor (which fits into the extension). They are threaded at the base so you can add filters (2" filters of course), they will slot into the focuser/diagonal, you shouldn't need them externally threaded, I think they will completely replace your current barrel.

 

[Commanderfish]

Thanks Rocky.  yes those look good, but there are no thumbscrews or compression rings on the focuser to hold in such a device; as I'm looking to replace the existing screw in barrel extensions there wouldn't be a compression ring.  Unless I can get it unstuck from the existing barrel extension which it seems to have welded itself to.  Unless you meant something else?

[rockystar]

The compression ring is built into the extension tube, you twist the top to secure the eyepiece - even though not shown on the picture, my 50mm came with a thumbscrew, and the 35mm has a hole for one (not sure if it should have been supplied).

EDIT: I think I may have misunderstood - sorry, not familiar with your specific scope

[Commanderfish]

Ah right I think we are talking at cross purposes - I understand that the extension tube has a compression  ring to hold the eyepieces, but my focuser drawtube won't have a compression ring to hold the extension tube - so the extension tube needs to be a screw on type.  I think.

[rockystar]

I see, hopefully someone with the same scope will be along soon then to offer better guidance. Sorry I can't help more.

 

[Commanderfish]

Thanks for your help!  I might yet be able to use the Altair ones you posted if I can get the compression ring off my existing extension tube...

 

[Commanderfish]

Hmm, is the width of a 2" focuser tube the same thing as an M56 fitting - like the Baader Click lock?