Astorix

Hi Tom, welcome to SGL

First off let me say, if you are using the barlow that came with the scope it should work fine. However when you are using the Barlow with the 10/25mm you are looking at objects with a much higher mag.

If your FL is 300mm then a 10mm with barlow would give you a 60x mag and with the 25mm a 24x mag. This should be fine to focus on pretty much anything in the sky.

With higher magnifications you will find that the exact spot of focus is actually very small. To the point where even turning the focus just 2 to 3mm more to the left or right can mess up the focus. I find that it is easiest to put the focus all the way to one end and then extremely slowly move the focus untill you find the focus.

You could also be experiencing vibrations which gives the effect of unfocused images. Are you placing the scope on a sturdy object and away from traffic which can send vibrations through the ground.

Hope this helps,