Extension tube problem (possibly really silly question.)

[FPM]

Hello

150mm Skywatcher dob.

The only way I can get a 2” extension tube to fit in the focuser is by removing the gnarled ring which holds the two fixing screws, but if I do that, obviously, I have no way of locking the tube, and therefore my shiny new 2”eyepiece, in place.

am I failing to understand something here???

thanks!

 

[Cornelius Varley]

Can you provide some photographs of the problem ?

[John]

The 2 fixing screws on the gnarled ring on the focuser tube should clamp around the flanged end of the 2 inch adapter. There should be 2 screws at the other end of the adapter to hold the eyepiece in place.

 

 

[bosun21]

What make of dobsonian do you have? The Skywatcher dobsonian should come with two extensions. 1 x 2" and 1x 1.25". Do you have a photo of the extension that you are trying to fit?

[FPM]

Many thanks. Photos attached. 3rd picture shows scope details (and 1.25 eyepiece in place).

i bought the scope 2nd hand, and it did not come with a 2”ext tube. Photos 1 and 2 show what happens if I try to use the newly-bought ext tube recommended by FLO. The first picture shows the large gap I get if in only partly-insert the tube (post it note applied to help with visibility for the photo). The second picture shows the ext tube being marginally too wide to fit inside the knurled collar. 
 

as mentioned, if I remove that collar, the tube fits fine, but as far as I can see that leaves me with no way of locking the tube into place within the focuser.

[FPM]

… it now seems that only a genuine Skywatcher tube will work. The one I have is about 0.5mm too large…

[bosun21]

The second photo shows the extension piece correctly fitted. It doesn't go in any further. It looks like a 35mm extension you have there. The 2" Skywatcher extension that comes with the scope is actually 47mm. You are 12mm short if this is the case. Using 1.25" eyepieces also require an extension. The Skywatcher one is the same as the 2" ie 47mm.

Edited May 18 by bosun21

[John]

Skywatcher have used a rather unconventional approach to eyepiece adapters with some of their scopes I'm afraid. 

 

 

[Kon]

You can either try source a skywatcher 2" tube or add a Baader clicklock adapter.

 

https://skywatcher.com/product/2-eyepiece-holder-for-dob-50mm/

If you are after 1.25" then

https://www.rothervalleyoptics.co.uk/skywatcher-2-125-eyepiece-adaptor.html

 

Edited May 18 by Kon

[FPM]

Thanks all. I’m in the trail of a SW tube.