If you cropped these both you'd have your basic police mug shot.
I think you're too far from the subject in both. The house in the background in picture two is distracting. Lighting looks ok....maybe work on posing. He looks very nervous and stiff in both and the straight on camera position isn't flattering to anyone.
I'd suggest if this is a fist attempt at portraiture to concentrate on just that. You say this is also the first time you've used a fully manual lens so now you have to concentrate on all of the things that go into making a good portrait and filly farting around with making this lens do what you want. You're creating handicaps where you really don't need to.
Look at some posing ideas here and online and keep experimenting.
thanks for the feedback! I agree on all points. Lots to learn and I definitely tried to bite off more than I could handle.
When I go out again, I will use my 50mm instead so I can focus on composition and try and give my model a bit of direction.
If it was perfect right off the bat, it'd take the fun out of learning!