Presumably
the A stands for Automatic Exposure control. The Nikonos IV-A is a
completely re-designed camera. Using technology from Nikon’s SLR’s, the
Nikonos IV-A has automatic exposure control with through-the-lens
(TTL), center-weighted exposure metering of aperture-priority. The
mechanical shutter was replaced with an electronically controlled one
with a speed up to 1/1000 of a second, another improvement from 1/500
on the older models. Camera controls were unified with other Nikon type
controls for ease of use. A hinged back was incorporated allowing for
ease of loading and unloading, a huge improvement over the previous
models where the outer casing was vertically disengaged from the body
frame. An LED display for metering and a ready light for flash are
incorporated in the view finder.