Focuser differences SCT and Newt- why?

[markse68]

I emailed Ron at Moonlite about their products as I’d like to use one of them on my planned dob build but see more of the SCT version come up second hand so wondered about fitting one of them instead of the newt version and I’ve seen many with the dual rate knob in mint condition for less than the single rate newt version is new 🤔

His response had me a bit confused though. He said that the CS version (SCT) is taller, the CR version (newt) lower profile and with much more travel.

I can understand wanting a low profile to bring focal plane closer to the tube to enable smallest possible secondary size if desired, but why would the newt need longer travel for the same eyepieces? Or is it more that you just can’t have long travel on an SCT? And why make the SCT version taller if it can be shorter like the newt version, though I guess if the bearings are wider apart it’ll handle heavier loads?

Mounting would be an issue but I was thinking of having printed a nylon adapter with the inverted conical part to mate with it giving the advantage it could be easily removed for transport or even rotated should that make for more comfortable focuser knob position.

Any reason not to do this if I can live with constraints?

 

[andrew s]

I suspect it is because with an SCT you can do course focusing with its built in focuser so only need to trim with the add on. While, with the Newt you do all the focusing with one focuser.

SCT will be taller as the focal point is well out from the visual back.

If you can use a tall focuser with out vignetting the Newt then no problem.

Regards Andrew 

Edited July 28, 2019 by andrew s

[markse68]

Ah I didn’t realise that was how it was meant to be used in an SCT. They do seem to only have .85 or .95” travel so I need to work out if all my eps will focus 😬