I must be dumb. Baader variable extension

[toc (Tim)]

I purchased one of these:

https://www.testar.com.au/collection...k-ring-part-33

I guess I must be over thinking it, but I cant figure out how this thing works. I get that I can move the inner male thread out and then lock it inplace, but all this is doing is exposing more of the thread, not making the adapter wider?

[Leo.G (Leo)]

There's only a total difference of 4mm.

[toc (Tim)]

The issue is that if its just exposing more thread, then it wont change the spacing because the thread will just get swallowed up by whatever it gets screwed into.

[iborg (Philip)]

Hi

I haven't used one of these so I am just guessing here.


If you screw the adapter into something only one or two turns, then use the lock ring to fix that end in place.


Then screw into the other end, I think that would mean you are using the adapter at maximum length.


On the other hand, if you screw the adapter as far as it will go, then use the lock ring etc, you are now using it at minimum length.

I hope this makes sense.

Philip

[joshman (Josh)]

its 3 parts
2x M42 internal threaded bits, and a M42 External threaded part.


Screw the deeper internal threaded part onto your something.

Screw the external threaded part into that until it bottoms out
Use the lock ring to adjust spacing.

[toc (Tim)]

Thanks - was able to get it sort of working...I think?

At near its maximum adjustment it only has a tiny amount of thread holding it, so I would trust it personally.

[AstroApprentice (Jason)]

I agree the Baader 12-16 mm variable adapter is tricky to work out at first and even with experience, it is possible to over screw and everything suddenly falls apart. I found the one linked below a much better design (albeit twice the price!) and the 15-18 mm spacing covers a similar range
https://www.testar.com.au/products/m...MaAtHoEALw_wcB

[Ryderscope (Rodney)]

FWIW, I’ve been trying out the Baader M68 15-18 variable extension. Whilst the concept is good I find that unlocking the “locking” ring results in the whole unit unscrewing from what ever it is screwed into, particularly once it has been secured in the image train. I was hoping that it would allow me to make small adjustments to the back spacing without having to disassemble the image train but it doesn’t appear that this will be practical. For now I have gone back to a combination of extension tubes and thin spacers.

[Joshua Bunn (Joshua)]

Im making a variable extension adapter with built in tilt adjustments, at the moment for someone. It has +/- 2mm of variable spacing and this version only consumes 22mm of backfocus (including tilt adjustment). One of the good things about it is there is no unlocking of threads to adjust the backfocus. I will post details of it when its finished.


regards
Joshua