We discuss the quantitative location of objects from holographic image
s when the reconstruction wavelength differs from the recording wavele
ngth. The holographic image equations are interpreted in a way that cl
arifies the meaning of stereo pairs of holographic images and indicate
s how backprojection methods can be used in holography to locate objec
ts. Alternative methods involving the production of distortion free ee
regions in the holographic image field during reconstruction, the use
of self-calibrating objects in the object field during recording, and
triangulation can be used to locate objects. (C) 1998 Optical Society
of America.