Difference between revisions of "Troubleshooting Holograms"
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Latest revision as of 00:08, 12 May 2013
- 1 Troubleshooting
- 1.1 Image Missing
- 1.2 Image Missing parts
- 1.3 Image "Drippy"
- 1.4 Image Dim
- 1.5 Image has Rainbow Lines
- 1.6 Image has Circular Patterns (Bull's eye)
- 1.7 Reflection Hologram Blurry
- 1.8 Image has Black Lines on the Object
- 1.9 Entire Image has black lines on it
- 1.10 Image Flashes at Extreme Viewing Angles
- 1.11 Image has Black Lines on the Plate.
- 1.12 Plate is Completely Dark
- 1.13 Plate won't Turn Dark in the Developer.
- 1.14 Image Flashes Rainbows from a Specific Location
- 1.15 The image has black spots on the Emulsion
- 2 Diagnosing the Problem
- 3 Pictures of Defects
So you made a hologram! But it is either not perfect or not even visible. Don't despair. We all have made holograms that are blank or have issues. I am going to run down the list of mistakes I have uncovered.
Motion or improper developing.
Card left in the object beam or reference beam after checking beam ratios.
Image Missing parts
If the object is missing parts then the object was in motion during exposure. If the film is missing views then that portion of the film was in motion. Air bubbles in the index matching fluid will cause this problem.
This is caused by soft emulsions and/or excessive pressure during squeegeeing.
Under or over exposure. Motion of the bench or film. Beam ratios wrong.
Image has Rainbow Lines
Light entered the edge of the plate and bounced between the two surfaces. Make sure to block any light entering the edges of the plate during exposure and reconstruction.
Image has Circular Patterns (Bull's eye)
Dust under film when laminated to the backing plate before exposure.
Reflection Hologram Blurry
It is normal to only have 4 inches of usable depth. The actual depth is related to how narrow of a bandwidth you are using for reconstuction. If you are looking for greater depth adjust your development to narrow the reconstruction bandwidth. There will be a corresponding decrease in brightness. In an H2 set-up it can be the object beam was too bright. As measured at the film plane the object can not be brighter than the reference beam.
Image has Black Lines on the Object
Object moved slightly.
As you can see the piece of paper under the kitty moved causing the large black lines.
Entire Image has black lines on it
Laser changed frequencies during exposure (mode hop) or is running in two lines.
Image Flashes at Extreme Viewing Angles
Laser beam was reflecting off something on the table and reaching the plate. It is important to card off any stray light from the beam.
Image has Black Lines on the Plate.
The plate was moving during exposure.
Plate is Completely Dark
Overexposed. Fogged film.
Plate won't Turn Dark in the Developer.
Underexposed. Old chemistry. Forgot to add part B for 2-part developer.
Image Flashes Rainbows from a Specific Location
This spot is too bright/overexposed. If the object is very shiny try spraying with a flatting spray. Flat clear lacquer works if you can't find flatting spray. Rotating the polarization of the object beam with a 1/2 waveplate can turn off shiny parts of the object. Use a polarizer rotated to coincide with the reference polarization to view the object illumination as you rotate the 1/2 waveplate.
The image has black spots on the Emulsion
This is called burnout and is most common in image planed H2 copies. It can be corrected by:
- Composition, and pre-visualization of the location of the recording plane of the transfer (H2) within it,
- Cighting of the scene when making the master (H1) so as to avoid the highlights near the intended transfer plane,
- Possibly manipulating the polarization of the scene lighting to reduce the highlights,
- Setting the beam ratio by measuring the "object" light in the transfer recording plane at the location of the burn spots (which are easy to find by placing a card in the plate holder) and with a detector about the same size as an average burn spot,
- Using a beam ratio and exposure time that gives optimum performance at the location of the burns, and
- Using a processing regime that doesn't shrink or swell the emulsion as a function of beam ratio or exposure intensity.
Diagnosing the Problem
Once you have identified the cause it is important to figure out exactly what corrective action will help.
This is one of the most common problems. To find out if you are stable it is useful to make an Interferometer.
Pictures of Defects
Here is a hologram that is "drippy" or has "rainbow lines". It was caused by laser light entering the edge of the plate during exposure. Either design your plateholder to block light entering the edges of the plate or tape the edge off with electrical tape.
This hologram shows "woodgrain". It is caused by the laser light reflecting back and forth from the front to the back of the plate. Make sure you have the corect polarization of the reference beam and make sure the reference angle is somewhere near 54 degrees (Brewsters Angle).
This hologram shows the difficulty of making a hologram of paper. Here the paper moved, either because it was not trapped tightly enough or because it was changing humidity durring exposure.
Here is a hologram showing plate movement. The dim spots do not change based on view point.
This hologram was underexposed. You can tell it is under exposed because it is dim and it is even dimmer at the edges where there was less light. If the edges were brighter then you would suspect over exposure.
This hologram shows "Burn Out". The little finger is very reflective and was placed too close to the film plane. You can see the black smear above the finger tip.