A camera comprises a spatial modulation optical filter that is disposed in a
viewfinder
optical system for subject observation at or near a position optically equivalent
to an estimated image forming plane of a photographic optical system and modulates
a subject light flux entering via the photographic optical system with transmission
characteristics to obtain a light flux having a predetermined spatial frequency;
a photoelectric conversion device that outputs a signal corresponding to detected
light; an optical element that guides the subject light flux having been modulated
at the spatial modulation optical filter to the photoelectric conversion device;
and a focal adjustment state calculation means that calculates a focal adjustment
state of the photographic optical system based upon the signal output from the
photoelectric conversion device having received the modulated subject light flux.