Camera with a holographic indicator

Claim 1

A camera having a holographic indicator comprising: objective lens means for forming an image of an object on recording means; exposure control means for determining the amount of exposure of said recording means; and a view finder including: a image forming optical system for directing the light from said object along a path and forming a second image of said object on an image plane; a relief type blazed hologram for recording the information of the indicating mark and having a transmitting factor high enough for the second image of the object to be observed and a diffraction efficiency high enough for the reconstructed image to be observed, said relief type blazed hologram having a diffraction grating condition wherein phase factor α defined by the difference in refractive indexes between said hologram and the ambient contacting therewith multiplied by πΔ/λ is not more than 0.56, where Δ is the height of relief and λ is the wavelength of incident ligh, whereby the zero-order diffraction factor of the hologram for the light from the object is higher than 90%; carrying means for holding said relief type blazed hologram in said path of light from the object; illuminating means arranged out of said path for illuminating said hologram to obtain a reconstructed image of the indicating mark on the same plane as that of the second image of the object; and optical means for viewing the reconstructed image and the second image; said illuminating means being arranged to illuminate the hologram from such a direction in which the transmitting light through the hologram passes out of the path of said optical means, and said hologram having a spatial frequency which causes the light from the reconstructed image to pass through said optical means and each diffracted light from the object to pass out of said optical means.