Maybe you could post some of the setting's data so we can help pin it down. At my age, I found when shooting around 135mm, handheld, I was not getting crisp detail. This was due to hand shake, easily contolled with a tripod.
Small aperatures used in landscapes do affect shutter speeds to the point that handshake could come into play if you are not using a tripod. DOF also plays a large roll.
Jerry Jaynes Great Smoky Mountains of North Carolina