ZWO - Takumar adapters, filter wheel - questions

[John78]

So I have a SMC 200mm f/4 and I want to connect it to a ZWO ASI120MM (for now!) - I've 3D printed a compression adapter temporary which works and is the correct back focus.

What I want in the image train is the ZWO filter wheel....

https://astronomy-imaging-camera.com/products/accessories/filter-wheel-5-position-1-25″-manual/

What I'd expected it to come with would be a M42x0.75 gender bender so you could just screw the camera straight on the end of the filterwheel, then I'd buy a M42x1 to M42x0.75 adapter to screw it onto the other side of the FW and it would be job done.  Apart from the M42x0.75 gender bender isn't included and actually I can't see one easily online.

So if I use the 1.25" nose piece screwed into the camera and the compression ring and just the M42x1 - M42x0.75 adapter ther other side I suspect it's going to be very tight to get the within the back focus distance.  (Then if I'm using the nose piece then I don't really need the FW I can just screw the filter into that)

So the question to those that have done this is - what combination of adapters did you have to use?  

 

Is the best plan simply to fabricate a 10mm M42x0.75 threaded tube and screw it into the camera and the filterwheel??

 

Confused - so any pointers helpful before I pull the trigger on the FW.

[John78]

So to answer my own questions, the nose piece will never work - I've thread locked (low strength) the supplied M42x0.75 -> C ring into the camera body and removed the wide angle lens from it...

Now that will screw into the filter wheel straight (with the option for 2mm spacer if required) and I've attached the lens with an M42x1 -> M42x0.75 adapter...

With the camera flush to the FW I've got a back focus distance of 38.72mm and the lens has already been adjusted to be 44mm to get it to focus on my 1000D, so I need 5.28mm to be perfect - but it does seem to be able to focus at infinity OK at 38.72.  I've got the option to go to 40.72 with a 2mm shim if it will be better?

So now I just need to print out some rings to hold it onto the mount and can have a real test.

 

What is the draw back if any of being within the back-focus distance?

[John78]

The almost finished article ready for first light...  need to reprint the camera top mount it interferes slightly with the fw central screw.