The original Pen F has a double-stroke film advance and a distinctive logo rendered in a gothic font.
The later Pen FT added a single-stroke film advance, and an uncoupled, integrated light meter, which uses a system of exposure numbers rather than f-stops.
The exposure numbers were added to the aperture rings of later Pen F lenses; the rings could be pulled out and rotated to show conventional f-stops instead.
A side-effect of the FT's light meter was a dimmer viewfinder.
Half frame means that the camera uses an 18×24 mm vertical (portrait) format, producing twice the pictures on a roll of 135 film as the regular 36×24 mm format.