Self-centre adapters

[JamesF]

I can see how these ensure that the eyepiece is correctly centred within the adapter, but what actually ensures that the adapter is centred perfectly within the focuser drawtube?

James

[Keiran]

James, I think it depends which one you buy, but the one that i saw was a snug fit in the tube, so when you did up the thumb screws they were just to stop it from sliding out.

Keiran

[John]

That was the question I asked a while back on these things James.

I'm not sure I ever found the answer !

I would have thought that you would need a self-centering mechanism fitted to the 2" drawtube to ensure that the adapter is itself centered ?

When I was messing around with Chromacors in refractors I added a 3rd set screw to the drawtube which enabled a degree of precision in centering the Chromacor in the drawtube. The Moonlite focuser that I currently use has a 2" compression ring fitting with 3 set screws, each 120 degrees apart so I guess that would allow fairly precise centering too.

[JamesF]

James, I think it depends which one you buy, but the one that i saw was a snug fit in the tube, so when you did up the thumb screws they were just to stop it from sliding out.

Keiran

That's what I assumed must happen from the looks of the ones I've seen, but it kind of suggests that people can make focuser drawtubes and the adapters to much better tolerances than the eyepiece barrels and I don't see why that should be.

James

[JamesF]

I would have thought that you would need a self-centering mechanism fitted to the 2" drawtube to ensure that the adapter is itself centered ?

That or some sort of external centering mechanism on the other end of the adapter to allow it to centre itself in the drawtube.

I can see that they have other benefits, but at the moment I can't work this one out.

James

[rory]

i cant say how accurately they bring the eyepiece within the drawtube,although i took out the 2"focuser houseing to see if theres obvious movement when tightening the thumb screws to hold the centring adapter in place. its a snufg fit so i couldnt visually notice the screws force the adapter off square as such, but then theres accuracy and accuracy i suppose.

the bennefit for me is ease of swapping e/ps, i think i could where chunky gloves if i wanted to and id be able to swap e/ps without a problem. then theres the point that you wont mark your barrels ,i only have modest eyepieces ,but for those with treasured e/p's you might like that fact. also you can put in a 2" filter then swap your 1.25" e/p's to get different magnifications without having to change over the filter to the e/p ( although that does not apply in my case as the thread is dented)

i know you probably know of the plus sides already ,but incase anyone else flicks through this thread they'll get an idea.

im sure there is a centring adapter now being sold cheaper than the others ,i read somewhere on the forums.

revelation adapters found it . http://www.telescope...pter-1.25-.html although i dont know if they are threaded or not.

[rwilkey]

I have the Orion Centering Adaptor and use it all the time as it is more convenient than fiddling about with set screws, as all you do is place the eyepiece in and then twist-lock it, most convenient. But if you have a compression ring on your focuser as I do I would imagine it is centered very well.