Low profile focuser for Newtonian, future proofing

[Danack (Dan Ackroyd)]

Hi,

I currently have a 130mm skywatcher newtonian that I would like to attach a dslr to, but I need a lower profile focuser to achieve prime focus.

I could get one that's explicitly designed to fit a 130mm newtonian, but I'm planning to upgrade to a larger tube at some point in the future.

Would I be okay to get one that's designed to fit say a 170mm tube and then say sand out a piece of wood to act as a filler for the gap, or is there something in the design of low profile mounts that would stop that from working?

cheers
Dan

[alistairsam]

Hi Dan
Which low profile focuser were you looking at? Mounting limitations vary.

You'd normally upgrade to a 200mm ota from 130, so I'd suggest calculating based on that.
With the 130mm, you could move the mirror up a bit with longer bolts and springs rather than fit a large focuser, else you'd have to make an adaptor plate or fill the gap but key is to make sure the focuser is perpendicular.
You can do that by using a simple collimated laser with the existing focuser, make a small mark on the inside of the ota of where the beam lands, then change the focuser and adaptor and make sure the beam hits the same spot.
You'd need to temporarily remove the spider and secy.

[Danack (Dan Ackroyd)]

Originally Posted by alistairsam

Hi Dan
Which low profile focuser were you looking at? Mounting limitations vary.

I had been looking at a couple on Bintel - but they seem to have disappeared.

With the 130mm, you could move the mirror up a bit with longer bolts and springs rather than fit a large focuser, else you'd have to make an adaptor plate or fill the gap but key is to make sure the focuser is perpendicular.

There's only about 1cm before the casing around the end of the tube - and it sounds like moving the secondary would be quite a bit of work. It couldn't be that hard to make an adapter plate could it?

[Waxing_Gibbous (Peter)]

Hi Dan,
Adapter plates are cheap as chips - or even free when you buy a focuser - so I would simply get a top-notch focuser such as a Moonlite, JMI or Feathertouch and ask the supplier to send adapters for both sizes.
Any of these companies should be happy to help you out via e-mail and FWIW I prefer Moonlite's offerings as they're a little cheaper than JMI or FT and the people there gave me lots of good advice.
Best of luck!