This is a streamlined viewfinder that will give you some idea of what your 100mm lens is about to take a picture of. "Some idea" because there are no framelines here, just an image with a black mask at the edges, and the eye relief isn't great. It's clear, though, and the built in parallax adjustment is effective. Assume that this will let you know what you're pointing at rather than what your picture is going to look like and you'll have a better time with it. In excellent cosmetic condition.