What Diameter tube for Dob....help needed

Hi All

I will shortly be making (or trying to make) an 8" dob. Having pestered all and sundry to keep an eye out for some wavin pipe for me, I took delivery tonight of a piece of wavin with a 9" internal diameter. Most sources recommend a tube that is 2" wider than the primary mirror. Will a tube with a 9" diameter be ok or should I keep on looking for a 10" diameter tube...Thanks in advance

Hi Trevor
I have an 8" mirror in the 9" Wavin ,no prob also added advantage of being able to get an end cap as a cover ,If you want to paint it use a product called ESP by a company called OWATROL www.IGOE.ie email:-
Owatrol@igoe.ie
Dont be afraid to ask any Q's
Eugene

Thanks Eugene.

I am sure once i get stuck in,I will have lots of Q's. At least the hunt for tube is over, one thing though, it is much heavier than I thought

Trevor,

Ideally 10" would be great but 9" will work fine too. Especially if you give the new scope time to cool when you take it outside. The narrower diameter will allow tube currents which creep along the tube wall to enter the light path. However as long as the tube is given plenty of time to cool then all will be well. On the positive side a narrower tube means you can use a smaller secondary, meaning a smaller central obstruction, and thus higher contrast.

Have you got your mirror yet. I see an 8 inch mirror going on ebay at the moment, current bid is around 127dollars. Might be worth considering.


Good luck with the new scope

Hi Dave

No, I have not got the mirror yet but it is on order. it is an 8" f5 manufactured by antares optical and supplied by an ebayer

stores.ebay.co.uk/ScopesnSkies

I have already purchased eyepiece from them...Great prices

Trevor,

There is a program that I found after I had done all the calculations the hard way when I made my own 'scope.
The program is simple and makes trying different dimensions for the various parts of the design easy.

The progarm is Newt for Windows home.att.net/~dale.keller/atm/newtonians/newtsoft/newtsoft.htm

A quick check of your spec shows that you would be fine with a 9" ID tube as long as the focuser (preferably a 2") is tall enough.

Michael