I've been browsing some Digital Holography papers these days, and have come across this fundamental question.
When you reconstruct the complex amplitude for the object image, you use e.g. Fresnel Transform to simulate diffraction.
The thing is, one of the parameters in this process is the distance, d, between the holographic plate (or CCD) and the object.
However, the whole point of Digital holography, I believe, is to find out the depth profile of the object, that is to say, the value of d.
We wouldn't have to do DH in the first place if we had known the precise (down to nanometric realm) value of the distance!
Could anyone clarify this for me?