Normal use is to insert the Barlow in the diagonal, and the eyepiece in the Barlow.
I would guess that it's just way off focus - especially if it can't seat fully in the diagonal.
Try using it on a terrestrial target in daylight hours to find out how much focuser adjustment you need (and which way to turn the focuser) when swapping the Barlow in and out. It's a LOT easier to experiment with new items in your optical train (Barlows, cameras, etc) in daylight (or pick a bright terrestrial target such as a distant streetlight if working at night), when you can get enough information from even a badly out-of-focus image to work out which way you need to adjust the focuser, which can be extremely difficult when you are looking at dim star fields.
|