Transmitted, vertical
A transparent specimen is viewed through a microscope using transmitted light while an opaque object requires vertical illumination.
Transmitted light is the light that passes through an object. Transmitted light microscopy is any kind of microscopy in which the light is transmitted from a source located directly across the specimen from the objective. The light is commonly passed through a condenser in order to focus it on the specimen to obtain very high illumination. After the light passes through the specimen, the image of the specimen moves through the objective lens and later to the oculars where the enlarged image is viewed.