Yes, it is a little soft, but not far out - it should still sharpen up in post to produce a decent image.
Hard to say whether it is down to equipment or technique, as the exif has been stripped so we can't see your settings. Did you use single point AF, in one shot mode, and focus on the edge of the glasses for a good contrast (using the vertical or horizontal edge if using a horizontal or vertical only AF point). Suitable shutter speed and aperture?
Assuming it isn't down to the camera settings, are you sharpening the shots correctly in post (or in camera if shooting jpeg and not doing further editing)? If resizing, do you sharpen afterwards as resizing will soften an image?
I haven't used that lens, so I don't know how the results are from a typical example, but that may be fairly normal for that lens. Do you have a filter on it? Sometimes a filter can cause softness issues if it isn't a high quality one.