I used the exact same method as Chris describes. I can get focus at prime and with 2 2x barlows in front in the train. I have not used a dob, so i can't be much help re that.
You will be able to get ok cluster images like the ones on my fb but for Nebulae they need longer exposure and the image will turn out too blurry. Still good fun to try and see how much Neb you can get but it's not pretty lol.
As my mount is pure manual, 2 seconds at prime is pretty much the limit i can go before the image looks like one of my kids went crazy with the textas haha
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It would be really good if someone could lend you a t-ring like Chris showed in his post, you could try it, if you get focus, all well and good. Saves buying one if you won't reach focus?