Object illumination

These are all of the old posts from the first two years of the forum. They are locked.
Updated: 2005-03-28 by HoloM (the god)
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bruce

Object illumination

Post by bruce »

What is your favorite optic for split-beam object illumination ( fast mirror, lens,objective etc..)?
My film should be here soon so it's time to start herding photons around the table!
Bruce
JohnFP

Object illumination

Post by JohnFP »

Actully anything will work for the object illuminatin but I used to use microscope objectives mounted in a spatial filter, sometime with our without the pinhole. I used those mainly because my spatial filters were already mounted. Whatever is used try to make sure the optic is "behind" the plate for transmissions or blocked very well so as not to record a hologram of the optic itself.

Cannot wait to hear how you are doing!

Peace!
JohnFP

Object illumination

Post by JohnFP »

Actully anything will work for the object illuminatin but I used to use microscope objectives mounted in a spatial filter, sometime with our without the pinhole. I used those mainly because my spatial filters were already mounted. Whatever is used try to make sure the optic is "behind" the plate for transmissions or blocked very well so as not to record a hologram of the optic itself.

Cannot wait to hear how you are doing!

Peace!
Dinesh

Object illumination

Post by Dinesh »

It depends on the object and how far it is from the plate. Certain things you have to watch for is not to use a piece of glass, or, if you do, use a thick piece and/or a fairly large angle. The reflections from the front and back of the glass will create fringes on the object. If the glass is thick, or the angle is steep, you may be able to isolate one of these reflections. Remember also that the reference is usually Gaussian but, depending on how you illuminate the object, the object wavefield may not be. This creates variable ratios on the plate. How you deal with this depends a lot on the film, its exposure and processing. Watch your polarisation. If the object depolarises, the ratio is not what it appears.
In the end, think that the light from the object has to interfere with the light from the reference. In order for this to happen, the reference and object must see each other. When this happens, the reference faithfully records whatever it sees. I know this is obvious and simple but I've seen set-ups where the majority of the object light did not co-incide with the majority of the reference.
Lighting is also a major feature. A badly lit hologram will look "Bleah!" We sometimes spend an entire day just lighting. Well, Joy does. She's the artistic one. I'm the equation meister, I just calculate!
Colin Kaminski

Object illumination

Post by Colin Kaminski »

I have used lenses, mirrors, concave mirrors, frosted glass, spatial filters, metal balls and broken frosted light bulbs. It depends on what kind of light you are looking for. Look through the plate holder at the object with a polarizer before you use any film. I like to make sure to look at the object for at least 30 minutes to look for composition, shadows illumination. I then make sure to look at the hologram for 30 minutes before I make any changes to the lighting. It sounds kind of slow but I find this is not the place to rush.
Larry

Object illumination

Post by Larry »

I then make sure to look at the hologram for 30 minutes before I make any changes to the lighting. It sounds kind of slow but I find this is not the place to rush.


I agree. If you are going to make a hologram that appears as though the noon time sun is shining down on the object, but you illuminate your object from the side (without rotating the object), you won't get the imagery across, it won't seem natural. Take your time to imagine what the final hologram should look like, and take a good look at all the asthetics of the image after its made.

You have so much other stuff going through your mind about how stable is everything, exposure times, is the beer cold yet...it really does help to slow down and view what you've done before makeing any changes.


dave battin

Object illumination

Post by dave battin »

Colin seems to have listed all possibilities,one that seems to work well, recycling lost light, is the first surface concave mirror. properly placed
it can recapture spillover light and refocus on the object(it usually is directed in to any area needed. the liberty hologram had about five in use


JohnFP

Object illumination

Post by JohnFP »

That liberty would look stunning with the torch very bright and "burning".
Michael Harrison

Object illumination

Post by Michael Harrison »

Anything that's supposed to be giving off light from a point source looks good when lit by an unspread beam. Don't forget to adjust the ratios so you don't end up with burnout.


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