NEX-7 and I not getting the detail...

This is a crop of one I took yesterday morning, I'm getting a bit dissapointed because I don't seem to be getting the detail in my shots that I would hope for, using legacy glass with MF, this was taken with: 1/125 ISO 100, f4, using a Nikon 70-210mm at full zoom with a fogar adaptor.

Is it because I shot it wide open? Is it the glass?

I'm expecting great feather detail e.t.c in these shots, and am a little confused as to why im not getting it....any thoughts or advice would be v.welcome....