Focusing with Barlow

[Hoopla]

Hi All. 
 

im hoping someone can help here. 
 

I have the following equipment. 
 

WO GT71

ASI533mc pro

zwo eaf 

2 x Barlow

i have no problem focusing without the Barlow but I just can’t seem to get any focus at all when I introduce the Barlow. I have extended the relief by adding extension tubes a very long way and not at all etc but after three nights trying I’m reach out to see if I’m missing something obvious here. Any thoughts or help would gratefully received.  

[Louis D]

Have you tried focusing straight through with an eyepiece, both with and without the Barlow, to see which way and how much it shifts focus?  Those results should carry over to the imaging setup.