i use the D7100 and i have noticed there are times when a subject seems out of focus through the viewfinder but actually turns out to be in focus
using a micro lens, the Nikon 85mm, part of the rear of the subject looked out of focus through the viewfinder yet appeared in focus when using "depth of field preview" button
and turned out fine when examining the pic later
is that common?
Read more: How accurate is a DSLR viewfinder?