Rigid image train - do I worry too much?

[ian_bird]

Hi

I have always been a bit (OK - a lot) obsessed with ensuring my imaging train is as rigid as possible. It used to be WO 98 FLT / Starlight Instruments 3" Feathertouch -> Tak72mm to Tak72mm adapter into my AO - which was directly attached to the OAG - which was bolted directly to the filterwheel - which was bolted directly to my SX H-18. Pretty rigid. My old flattener used to sit on the Tak to Tak adapter inside the drawtube on a M48 TS variable spacer - so it did not form part of the load bearing part of the image train.

I have now ditched that lot and gone to WO 98 FLT / Starlight Instruments 3" Feathertouch -> Riccardi Reducer/Flattener -> (and here is where it gets a bit dodgy) -> M48 TS variable spacer -> M48 15mm Extension -> Filterwheel -> M48 Male to Male attached to my new Atik 4000.

My question is - how rigid is the M48 bit going to be? Or am I worrying too much?

Cheers

Ian

[davew]

I'm presuming you're talking about the variable spacer ?

I asked Martin Farmer ( If you know of him ) some years ago about whether these could be rigid enough and he said yes, if they're made and used correctly. If you've taken out all play and tightened them ok then it should be fine.

If you weren't talking about the spacer then I've no idea why an M48 thread should be any different to any other 

Dave.

[ian_bird]

Hi Dave

Yes - I was primarily concerned about the variable spacer. But also M48 in general. Tak72 and/or Directly Bolted just strikes me as being a bit more "flex proof". That's why I was wondering if I worry too much. If M48 is as good as M72 then OK.

Not heard of Martin Farmer.

Anyway - thanks for the reply. Appreciated.

Cheers

Ian

[Gina]

Looks like it should be alright   I agree about a rigid imaging train.  Flexing will cause image shift but worse, slanting of the image plane.

[ian_bird]

Hi Gina

Yes - it's the slanting of the image plane that I really worry about. Not much point in buying a Riccardi Flattener if you are not orthogonal!

Cheers

Ian

[davew]

Hi Dave

Yes - I was primarily concerned about the variable spacer. But also M48 in general. Tak72 and/or Directly Bolted just strikes me as being a bit more "flex proof". That's why I was wondering if I worry too much. If M48 is as good as M72 then OK.

Not heard of Martin Farmer.

Anyway - thanks for the reply. Appreciated.

Cheers

Ian

Given enough load then I'd say that the wider and thicker the tube the more stable, but only so far. I don't think it'll make much difference at our level.

Marin Farmer produced one piece blocks for the Losmandy mounts. Knows a bit about engineering. I've been to where he works and there were one or two very space age things on the reception walls.

Dave.