take-up unit. If the cellophane or plastic material is slipped in next
to the cutoff blade (PH-637/PFP only), it can be torn off for disposal.
On Projector PH-637/PFP, the supply unit and the take-up unit are
attached to the right and left sides of the projector housing, respec-
tively. On Projector PH-637A/PFP, the roll attachment is built
into the housing; the supply unit is set into the top front of the hous-
ing, and the take-up unit is set into the back. Anything written in
grease pencil on the cellophane or plastic stretched on the projection
stage will be projected on a screen so that the viewer sees on the screen
what the writer sees on the projection stage.
e. Projection Head. The optical system in the projection head con-
sists of a 14-inch focal length lens and a front surface mirror. T h e
optical axis is centered over the optical axis of the housing. A win-
dow in the front of the head protects the mirror and lens from dirt,
scratches, and breakage. Light from the projector housing is pro-
jected through the transparency on the projection stage and through
the lens. It then is reflected from the front surface mirror to the pro-
jection screen for viewing. The entire projection head can be racked
up and down on the vertical support post to focus the image. T h e
vertical angle of the front surface mirror can be varied to center the
image on the screen.
f. Aperture-Plate Holder and Aperture Plates. An aperture-plate
holder and aperture plates are supplied to mask transparencies of
various sizes. The holder is screwed to the top of the housing over
the plate-glass cover, and the appropriate aperture plate fits on top
of the holder.