I've got mixed feelings about DOF adaptors, so let me start by saying this example I'd put amongst the better ones I've seen, so well done on that.
But, they all seem to give the same 'look', a kind of veiled appearance. The ones I've made have not been as good as this, but when able I'll get back to it and see if it can be sorted for me. It just seems like the images from them need to be 'lifted' somehow, difficult to describe really.
Anyway, other points. You're getting the classic vignetting thing sometimes, seems that nothing can be done about that, apart from one trick I have in theory stage which no one seems to have cottoned on to yet . In a number of those shots a DOF adaptor is not giving any benefit, so perhaps choosing the time to use one is important.
When you're foussing your Nikkor it's shaking the image a bit, perhaps a lever would help, don't bother with fancy photo accessories, just get a fishing reel tie for about £2 and put that on the lens, and maybe your tripod/mount needs to be a bit more ridgid. When I trialled HV20's I found the tripod socket is not very substantial, allowing the camera to move with little pressure, so maybe some additional support is needed with the weight of the DOF Adaptor being there, depends on what type you have.
So, which one is it? Commercial or home made?
Either way, some good stuff to work with .