Time for a change ..

[ZeroID (Brent)]

I built this scope, the RN8F8 about a year ago. A super lightweight, 8" F8 Newt using a Gary Nankivell mirror and secondary on guitar string suspension. Concept was longer focal length for almost coma free focal plane and minimal diffraction spikes with .3 mm E strings as the suspension components. Had a heck of a job collimating it as the guitar strings were very difficult to balance the cross loading so I parked the project for a while.
Recently I had another go at it but this time using 4lb fishing nylon, sprat line stuff and managed to get a better result with collimation as the nylon was less likely to break and had more stretch. Yeah, I know the purists will get onto me about it but I need to get this to work to at least prove the design. If it doesn't I'll go back to the drawing board for a new spider idea.
Anyway it's now up on the mount, aligned and waiting for the clouds to clear. It only just fits in the Ob between the walls and I've had to reroute a lot of cables to accommodate the extra swing but it should give me a better magnification for smaller targets, galaxies and the like without losing too much in exposure time.

[MattT]

I haven't built a wire spider but what about bass guitar g strings? Thicker than e strings by a bit.

[ZeroID (Brent)]

Originally Posted by MattT

I haven't built a wire spider but what about bass guitar g strings? Thicker than e strings by a bit.

Too thick I'd say, but there are options in between obviously. Cheap enough from China, normal G string might be a bit more robust. But they are buggas to handle and setup, all twangy and sharp ..

In the meantime, the clouds and thunderstorms have put paid to any testing.. Love to get some vid of Mars while it's up close.

[Wavytone]

Another solution is the wire used for control-line model airplanes - sod at specialist shops that sell balsa and tissue kits etc.

This stuff is typically sold in 30 metre rolls, it is stainless steel, has zero stretch and is a lot finer than guitar strings, about as fine as button thread. Only downside is it is so fine it will slice your fingers so wear gloves when working with it. There is a special technique too for terminating it in a loop that won't slip.

[ZeroID (Brent)]

Originally Posted by Wavytone

Another solution is the wire used for control-line model airplanes - sod at specialist shops that sell balsa and tissue kits etc.

This stuff is typically sold in 30 metre rolls, it is stainless steel, has zero stretch and is a lot finer than guitar strings, about as fine as button thread. Only downside is it is so fine it will slice your fingers so wear gloves when working with it. There is a special technique too for terminating it in a loop that won't slip.

I'm trying to find an EASY solution, not one that is going to shred my fingers !
As I said, I'll prove the optics first then deal with the secondary if necessary. It may prove to be a good option and I think just going up a couple of string thickness's or so from a guitar set should work better.

Actually if you want finger shredding capability I've got either some platinum wire or better still, tungsten wire from my Xerox Service Tech days. That stuff is lethal !

[Rac (Raymond)]

I use E strings on my 20" f3.8 dob. I adjusted them and set them up just under a year ago when I made the scope and have never needed to play with them since. I never need to adjust the secondary either.

It's using a very similar setup to Rolf's but I can collimate the secondary without playing with the wires.

[ZeroID (Brent)]

Thanks for that Raymond, might look at a similar configuration later. I kept mine pretty simple, all adjustment was in the machine heads, nothing at the secondary support. Got it pretty close to right but then a few strings let go and I got frustrated with trying to fix it.
In the meantime the weather has precluded any further testing, I'm just hoping Mars will still be around by the time the clouds clear off.

[Rac (Raymond)]

My strings are not very tight at all, well off snapping.

I'm glad I made the decision so I could still adjust the secondary and not need to play with the wires.

I've had a few good seeing nights up here in Whangarei. And this 20" now has goto and tracking with a stepper motor OnStep system.