Confused about thread types

[Nikolas (Nik)]

I see 3 inch focusers, 2.5 inch 2 inch etc then there ae the thread M63 M68 M57 M48 M42, how do you know what goes where? I know m42 and M48 but after that I'm totally lost What fits a 3 inch focuser? What fits the 2.5 inch etc?

[billdan (Bill)]

Hi Nik,

A lot of this stuff is vendor specific thats why people like Precise Parts make a fortune from manufacturing adapters.
Its not only the diameter of the focuser one has to consider but also the thread pitch that they used.

e.g

Takahashi 2.7" Focuser 72mm x 1.0mm thread pitch

Vixen VC200L Focuser rear thread 60mm x 0.75mm

GSO 8" RC rear cell 90mm x 1.0mm

Meade SCT 3.25" 16TPI

Celestron SCT 3.3" 16TPI

So your question what fits a 3 inch focuser would depend on who made it and what thread size and pitch they used.

Cheers
Bill

[Nikolas (Nik)]

Skywatcher, Explore Scientific and TS optics

[billdan (Bill)]

I just happened to have PDF user manual of the Skywatcher Espirit 120ED refractor which has a 3 inch focuser.
Looks like you need a M74 x1mm pitch to connect to the focuser.

[Nikolas (Nik)]

Originally Posted by billdan

I just happened to have PDF user manual of the Skywatcher Espirit 120ED refractor which has a 3 inch focuser.
Looks like you need a M74 x1mm pitch to connect to the focuser.

Thanks