Which extension tube to help get focus

[Adelong]

Hi I've got a skywatcher flexitube Dobson which will only focus if I don't fully extend the scope. I've read on here that by fitting an extension tube to the eye piece this will allow me to focus properly. I wondered what size extension tube I should get ?

Thanks

Ade

[Cornelius Varley]

Hello and welcome to SGL. What eyepiece are you using ? If you can only get the eyepiece to focus if you don't fully extend the telescope then adding an extension tube won't work. The tube will only move the eyepiece further away from where it needs to be. Are you focusing on something close to the telescope or the night sky ?

[happy-kat]

My short barlow on my heritage 130p does not focus if using that I think I dropped the trusses about an inch. Normal eye pieces are fine fully extended

[Scott]

Just a thought, but are you using both the 2" and 1.25" tubes? you are only supposed to use one or the other, not both. sorry if I'm stating the obvious

[ronin]

If you can only get focus by not fully extending the scope then you have insufficent inward travel an extension tube will only make it worse.

Sounds like Scott may have the problem. They often come with a 1.25" adaptor tucked inside a 2" adaptor, you are supposed to remove the 2" bit and refit the 1.25" bit. They do it for ease of transport but it looks as it it is supposed to be used like that and it isn't. Usally 60% or more of people have this problem at first.

With both in you cannot get the focuser to travel inward far enough, which seems to be what you describe.

[bomberbaz]

If you can only get focus by not fully extending the scope then you have insufficent inward travel an extension tube will only make it worse.

Sounds like Scott may have the problem. They often come with a 1.25" adaptor tucked inside a 2" adaptor, you are supposed to remove the 2" bit and refit the 1.25" bit. They do it for ease of transport but it looks as it it is supposed to be used like that and it isn't. Usally 60% or more of people have this problem at first.

With both in you cannot get the focuser to travel inward far enough, which seems to be what you describe.

as mentined twice, only insert either the 1.25 or the 2" ep tube. 

If you are not already doing this, you need to contact your retailer for more advice methinks.

ps, when dod you buy the scope?

[Adelong]

Yes I think I may have been using both. Thanks so much. This really is a great resource.

[Adelong]

I've had it 2 years without using it much. Mainly due to its size which I've found a solution in a cart which I'm getting made for it. I hope to now get to use it much more. Thanks to all of you for your help.