Help With Thread Pitches and Adapter Design

[russellhq]

I'd like to get a part made up that will allow me to screw a 2" filter into my reducer but still be able to screw the reducer onto my focus tube.

I've been searching about for thread sizes but can't find a conclusive answer.

Some say the 2" filter thread is M48 x 0.6mm and others say it's M48 x 0.75mm.

Also, I've read the thread on the end of the Skywatcher is M54 or M56 and the pitch is 1.0mm or 0.75mm

I've sketched what I think it is below:

Does this look do-able?

[Steve Ward]

Doable , but the adaptor from FLO works wonders , and is much easier to change filters with . . . http://www.firstlightoptics.com/adaptors/flo-adapter-for-skywatcher-focal-reducers.html

[russellhq]

I've got one but it doesn't work. There's a bit of slop in the focus tube which is causing focus issues across the imaging frame. I was going to attach the filter to a 2" extension tube, should make it easier to change.

[Astrobits]

SRB Film services ( as was, now SRB Photographic/SRB -Griturn ) do adaptors to customer specs. Try them.

http://www.srb-griturn.com/

Nigel

[SiriusB]

Commonly found astro gear thread details: 2" filter m48x 0.75mm pitch

1.25" filter m28.5 x 0.6mm pitch

T thread m42x 0.75mm pitch

SCT thread 2" x 24 TPI

Skywatcher focuser tube thread~ i think there are two versions kicking around, mine's external M56 x 1.0mm pitch, i think theres also an M54 internal thread x ?? pitch on some focusers.

Hope thats useful.