P3D Re: More hologram comments

[KenDunkley@xxxxxxx]

In a message dated 98-07-15 21:37:02 EDT, Bob Maxey wrote:

<< As far as your Holo of the carving, the entire image is still there.
 However, and this was not mentioned in my original post, the image is
 degraded to some degree. however, under proper conditions, the entire image
 can be reconstructed - quality will not be as good as it was originally. >>

Actually Bob I agree with many of your  comments, and do not wish to make any
one (including myself) defensive.  However, the redundancy idea you mention
has been quoted by many others before you, especially by persons who are
trying to quickly get across to other persons,  unfamiliar with the medium,
the astounding optical properties of holograms.  

The statement that the entire holographic image can be reconstructed from a
only portion of the hologram  is not quite true although most holographers do
not nit-pick it as I did in my initial correspondence.  It is definitely not
true with image plane holograms and it is only approximately true even with
the a laser illuminated and reconstructed Fresnel hologram.  The Fresnel
hologram is the basic laser hologram, without frills, that you describe.  

If you make a holographic recording of an apple with a worm hole on an 8x10
inch plate and subsequently break the plate into , say, one hundred separate
pieces. Each piece will, as you indicated , contain a full sized image of the
apple.  Understood in this fashion  your initial statement is "basically"
true.  

However,  I think you will agree that it is  more accurate to say that each
broken element of the hologram contains a full sized image of the recorded
object viewed from the perspective of the element in question. 

Thus, it may be possible for the worm hole to be seen from some of the broken
elements but not necessarily from all of them (depending how the worm hole was
initially positioned relative to the plate).  Elements from widely separated
locations of the plate will see different perspectives of the apple.   In some
you will see the hole and in some others you won't. 

Understood in this fashion it should be clear that most of the commercial
holograms do not meet the redundancy requirement you talk about because the
majority of  commercial holograms are (white light, rainbow, or reflection)
image plane holograms where the image straddles the plate.   Cut them and you
will lose portions of the image.  As I indicated in my first correspondence,
how much you lose is a function of the perpendicular distance of the image
point from the hologram. 

Respectfully submitted

Ken Dunkley


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