Try adding in one or more of the CS- to C-Mount-Adapter Rings between your Lens and the Camera. Should make the Lens a Macro Lens.
You could buy those in the Krontech Store or on ebay and Co. for little money.
Also use A LOT of Light and try closing down your iris a bit if possible or you will only have a realy Little Area of your Object in Focus.
Hi. This guy also used an additional cs-c mount adapter and the result is what I want.
https://www.youtube.com/watch?v=hs6VHjc-Gpo (starting at 4:12)
I'm also using computer 12.5-75/f1.2 and two cs-c mount adapter as you suggested, but I find it impossible to focus no matter how far or how close the camera is. Do I need to do some other adjustments? Thanks!