You cut the bottom off, not the top?
Interested in knowing why the collimation problem? Sounds like an extension tube was used in the focusser to collimate? I have an 8" imaging GSO reflector - I know because I need to add extension tubes to bring it to visual focus. But I have been collimating, without a problem, directly in the focusser - no extension tubes?
Err, you'll capture them, but you probably want a resolved image rather than a blur? Are you on a driven EQ mount?
Suggest you search out other's images of Orion and 47 Tuc and check what settings they are using.