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Magnified image hologram?
April 30 2003 at 1:11 AM | Tom B. (no login)
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| Is it possible to make a true hologram of an object in which it appears significantly larger, but undistorted? From Saxby's discussion of focused image holograms it seems that there are two problems with using a lens for other than 1:1 images 1) the axial depth increases as the square of the lateral magnification causing exaggerated perspective and 2) the parallax view angle decreases as the plate is moved away from the lens with increased magnification, so the useful viewing angle would be very narrow. I wonder if there might be some kind of clever setup that magically cancels 1) and 2) but leaves the magnification intact.
It occurs to me that I don't recall having ever seen any big holograms of tiny objects (other than stereograms or holograms of enlarged models). For example, a nice large full-parallax hologram of a real (dead) insect, say a dragonfly showing microscopic detail could be quite lovely. Can it be done?
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Colin Kaminski
(no login)
| | Re: Magnified image hologram? | April 30 2003, 1:21 AM |
This is a question I have been meaning to ask Dinesh. If I master a hologram at 658nm and copy it at 473nm does the scale change by a factor of 1.39?
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Vidar Hegdal
(no login)
| | Re: Re: Magnified image hologram? | April 30 2003, 5:39 AM |
The idea of making magnified holograms of tiny bugs sounds great, as these creatures looks great when magnified. As you write, I also suspect that one have to make 100+ adjactent digital photos and make a holoprinter on the table.
If it is possible to magnify a hologram without messing up depth in a simple way I will go right down to my lab and try it out.
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Jean D
(no login)
| | Magnified bug | April 30 2003, 6:16 AM |
Maybe we can make an hologram of a magnifier and a bug together as a master holo.
I've seen a hologram of a microscope, when 'looking' in the occular, we can see the object on the microscope slide.
Jean.
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HoloDisc
(no login)
| | yes, that works... | April 30 2003, 2:54 PM |
> Maybe we can make an hologram of a magnifier and a bug together as a master holo.
Now extend that to simultaneously encoding the 'magnifier' to deconvolute aberrations, achromatisize, and then to perhaps having specific mag. ratios when viewed from different vectors so perhaps the eyes of the bug are especially HUGE!... I think most think of Holographic Optical Elements as 'gratings', but they can simulate ANY optical function, even simple lenses. Extremely complex H.O.E.s! can be formed with somewhat 'simplistic' robotic setups.
On a side note....ever coat the concave side of a watch glass or other spherical dome and make a hologram of an object inside the dome using a converging reference. When played back with a standard diverging illumination... its cool!
On another side note... accuracy of reconstruction was suspended when the subject playback was required to be larger then the original...so WHY?!... does it have to be utterly faithful and lack all geometric distortion? The eyes of engineer/scientists can be SO discriminating! lol
I made a Cross Multiplex of a vacuum pressure sensor for a manufacturer's trade show exhibit. As I shot the 35mm footage of the sensor on a turntable, I moved the sensor way off center so that as it swung elliptically through the cylinder. It 'seemed' to ZOOM towards the wall of the cylinder when the 'de-encapsulated sensor chip in the top of the enclosure' was facing the viewer. I also placed a large magnifying lens between the sensor and the camera at that apex. When mounted on the motorized light fixture, at first, the Hologram was just plain WEIRD! and 'felt' distorted! The sensor got smaller at 180 degrees rotation and then got larger and larger as it came to center clock position, until about +- 10 degrees, when viewed through the magnifier...IT GOT HUGE! and the sensor chip could be easily seen up close. I was worried! I left it there for two days and passed it over and over in consternation. About 50 rotation views later, I started to like it!
When I delivered it, I was embarrassed and almost promised I would remake it!...but I 'balls it out' and stuck to my confidence and crossed my fingers instead. I went to the trade show to collect brochures and there was a crowd around the Hologram laughing and pointing!.... people 'LIKED' the weird ZOOM effect and they liked getting a closeup of the sensor chip when it swung around. I watched as engineers and scientists walked by and their eyes locked! on the display and it pulled them IN to get a closer look. Thus, IT was a success!, whereupon ...OF COURSE!! I knew it ALL the time! lol lol
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Kaveh
(no login)
| | Re: Magnified image hologram? | April 30 2003, 4:16 PM |
I agree with what Graham Saxby says, and I think it is safe to say that there is no simple trick to produce an undistorted image, using 'direct' holography of the object.
The different transverse and longitudinal magnifications lead to 'cardboard cutout' effects, when an image is reduced in size by using a shorter wavelength or a reconstruction beam different to that of recording. An example is a hologram copy of the famous hologram of Gabor sitting at his desk. I can't remember where I saw it, but it was on a 10X8" plate, so reduced several-fold. One could clearly see the image squashed, so Gabor looked like a cardboard cutout.
The only way I see is some kind of stereogram technique.
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Tom B.
(no login)
| | Magnified image hologram? | April 30 2003, 11:16 PM |
I suspected it would be difficult or impossible to do directly, otherwise I would likely have seen some examples. One approach I'm considering is to pre-squash the object to compensate for the depth exaggeration when magnified. This will require some practice with the fly swatter to control the amount of squashing  Perhaps objects with limited depth such as coins or shallow carvings might look interesting with depth exaggeration when magnified. The problem of restricted parallax view angle remains, though.
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HoloDisc
(no login)
| | Re: Magnified image hologram? | May 1 2003, 6:26 AM |
> The problem of restricted parallax view angle remains, though.
Use a large aperture aspheric lens. Or squash the bug on a convex surface! lol
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Anonymous
(no login)
| | Re: Magnified image hologram? | May 1 2003, 8:41 PM |
"One approach I'm considering is to pre-squash the object to compensate for the depth exaggeration when magnified. This will require some practice with the fly swatter to control the amount of squashing "
Insert catheter into bug. Attach other end of catheter to a bicycle pump. Squash bug. Inflate bug a little, take a shot, move reference beam, inflate bug a little more, move the reference beam, inflate... etc etc. Write paper: "Real-Time Growth Dynamics of Drosophila by Holographic Methods". Wait for Nobel.
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Dinesh
(no login)
| | squash bug etc | May 1 2003, 8:42 PM |
that last anonymous was me.
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