Question

What is the difference between photography and holography?
Explain holography technique to obtain 3D image of an object. 

Answer 1

Holography	Photography
1.The light from the object is scattered directly onto the recording medium in the recording of holography.	1.A lens is required in photography to record the image
2.A laser is required to record a hologram	2.A photograph can be recorded using normal light sources e.g.sunlight,etc.
3.In photography,only intensity is recorded so photography produces 2-D picture of the object.	3.In holography, both intensity as well as phase of light wave is recorded,thus holography gives 3-D picture of object.
4.5.There is a need of vibration less table for holography.	4.There is no need of vibration less table for photography.
5.When a hologram is cut in half, the whole scene can still be seen in each piece.	5.When a photograph is cut in half, each piece shows half of the scene.

Holography technique to obtain 3D image of an object:
1. Holography is the science and practice of making holograms. Holography is actually a recording of interference pattern formed between two beams of coherent light coming from the same source.
2. In this process,both the amplitude and phase components of a light wave are recorded on a light sensitive medium such as a photographic plate. The recording is known as a hologram.
3. Holography requires an intense coherent light source.It became a practical proposition only after the invention of LASERS.
4. Holography is a two step process.In the first step,recording of hologram is done where the object is transformed into a photographic record and the second step is the reconstruction in which the hologram is transformed into image. 

1.During the recording process we superimpose on the scattered wave emanating from the object,the another coherent wave(called as reference beam) of the same wavelength.
2.These 2 waves interfere in the plane of recording medium and produce interference fringes.This is the recording process of hologram.

Reconstruction process :

1.The reproduction of the image from the hologram is known as reconstruction of the hologram.
2.In this process,a wave identical to reference beam is used.
3.When the hologram is illuminated by the reconstruction wave,2waves are produced.
4.One wave appears to diverge from the object and provides the virtual image of the object.

5.The second wave converges to form the real image of the object.