Shortened german ranks

Hi
In relation to a book I'm writing about the german prisoners of war camps in Rogaland, I've come across a couple of ranks that I'm not shure about. They are shortenings:
- Obstubaf.
- Oschaf.
- O/Feldw.

I have just received help, and we think that "Oschaf." means "Oberscharführer".
Now I'm left with "Obstubaf." and "O/Feldw." (Feldwebel I guess, but the "O")
"Obstubaf." was used as a title/rank for a Obstubaf. Wilkes, which I'm pretty shure is Friedrich Wilkens, a sturmbannfuhrer in the SS. Why this shortening? He was "Commandeur der Sicherhetspolizei und des SD, Stavanger". Could it be Obersturmbannfughrer?
Anyone with a suggestion?

- Obstubaf. - Obersturmbannführer
- Oschaf. - Oberscharführer
- O/Feldw. Ober Feldwebel

I think this should be the right ranks.
Kurt

Thanks Kurt!
That's all I need.
Atle