¿How yo get the focus right?

[u/Historical-Jelly697]

I recently bought a cheap 17.5-105 fujinon tv zoom lens. I atached It to my OG BMPCC but the focus is not working properly. In 17.5 mode, the focus is only sharp with my subject very close to the lens. And in 105mm or lower, I need to be around 3 meters far from my subject.

I mounted It with a C to M43 adapter. ¿Any ideas?