Dimensions of Starwatcher Explorer 130 900mm tube?

[cwis]

Hi all,

I picked up the primary and secondary mirrors from one of these second hand, I have a new Svbony focusser (far nicer than the Sky watcher standard one - it's metal!) and I'm going to make my own carbon tube - I've got some cloth and resin left over from a motorbike related project.

I only have one question - how long is the tube? I have two estimates from pictures online of 850mm and 700mm - if anyone has one can they please measure it? Any usable dimension is fine, overall length, distance from the secondary "cell" to the primary, whatever is easiest.

Many thanks!

 

 

[DaveL59]

not sure if it's the same scope but I have a SW130EQ2, no idea if it is a parabolic or spherical mirror or if that'd affect the dimensions. Happy to measure up the tube tho if it'd be useful. I would say there's probably no harm in extending the OTA out beyond the secondary a bit further than the SW tube is to prevent stray light and maybe help with dewing, tho others more experienced in building will likely know better than me.

Measured from the mirror end of the tube (mirror fitted so the end of the cell block) up to the centre of the focuser is 74.5cm and to the top of the tube 83cm.

Edited December 28, 2020 by DaveL59

[cwis]

Many thanks!

I think I've got the spherical mirror one - like you I'm not sure whether that has a bearing - a focal length is a focal length - right?  I'm going to go with the stock secondary cell to begin with so both dimensions you have given me are very useful!

I've got a bit of plastic pipe that I can cut and use to test and then wrap the carbon round - I'll get on with cutting it for a mockup! Thanks again!

[cwis]

Focusser test fitted! Just need to make up some v blocks now to rotate the tube on while I cut it to length as marked.

[cwis]

V block assembly worked OKish - will need to rethink that to cut the CF tube. I've slapped it together precariously to see if the focusser is in the right place. With it all the way out I should just be able to focus on the end of my garden...

 

And that's a yes! Excellent!  Next steps are to 3d print some stiffeners for the tube to make it round, and then use it as a former for the CF tube. I'm going for usable, rather than pretty so not bothered with surface finish. It'll be grippy rather than shiny!

Here's the project the CF is left over from... BMW R100 café racer tank.