It's just a regular step down ring machined with a recess to fit a baby death lens closer to the camera lens.

I still have a little vignetting in the lower two corners, but that's as low as it can go. I would have to zoom in or machine my baby death to get rid of the remainder--not gonna do it.

Thats sick dude, looks so much better with less vig. What are you using, the flat thread converter?

No. I machined a step down ring for a custom fit to my lens and camera. A flat thread converter can do the same thing as a long as it's not too tall, but either way you really need to customize it to get rid of the most vignetting.

Yea but dont you lose wideness and distortion when you bring the lens closer like that. you should do a test for us, would be very appreciated

There's no "testing" to do because, as you pointed out, it's a tradeoff. Do you want less vignetting at the expense of width or is the vignetting ok with you? I decided that the vignetting was too much and the loss of width is something most people wouldn't notice.

If you think it "looks so much better with less vig" then you probably won't miss the extra width.