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jdowning
Oud Junkie
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Registered: 8-2-2006
Location: Ontario, Canada
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The tiny 'krypton' filled lamp (full of infra red wavelength light) has been soldered to a longer lead and connected to a battery supply (2 AA Ni-Cad
rechargeable batteries in series, total voltage 2.4 volts. Standard Alkaline batteries at 3+ volts would quickly 'burn out' the lamp). Low voltage,
low heat means a safe application.
The lamp was tested on three of my instruments - lute, baroque guitar and vihuela - each with a sound hole covered with a rosette. The lamp was fed
through each rosette to illuminate the instrument interior and the soundboards photographed with the modified Vivitar camera (visible + IR). Although
the illuminated area and light output is small (but the lamp can be easily moved around to compensate if necessary) the bracing geometry can clearly
be seen (viewed by the camera but not by the naked eye). Note that the illumination is more uniform in the lute where the bowl acts as a curved
reflector to focus the light compared to the flat backed guitar and vihuela.
Clear focussing of the image requires improvement (with perhaps a different camera with longer focus than macro to cover a full sound board) but,
nevertheless, I suspect that it will not be possible to bring the hidden bracing into sharp focus through the sound board wood (a similar problem is
found with Xray imaging). Nevertheless this non destructive imaging technique may provide useful information for the luthier at little cost for the
tool.
For those instruments played with the support of a shoulder strap access for the light source may alternatively be provided by removal of the strap
button.
[file]26472[/file] [file]26474[/file] [file]26476[/file] [file]26478[/file] [file]26480[/file]
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jdowning
Oud Junkie
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Location: Ontario, Canada
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Moving a bit off topic - but related - posted here only for information for those interested in exploring the scope of infra red imaging.
The modified Vivitar camera - as previously reported - works quite well at close up and macro imaging despite the basic simplicity of its lens.
The modified camera did not work well for long distance (landscape) images that were out of focus. The lens module has, therefore, been further
modified to allow in focus landscape IR imaging.
The IR cut filter on this camera was located in front of the lens and so acted as a spacer about 1 mm thick. Removal of the IR cut filter therefore
resulted in the lens being moved that distance closer to the CMOS sensor. As it happens, there was then insufficient adjustment in the lens module to
manually correct the long distance focus of the lens.
The lens module was, therefore, then dis-assembled again and a leather washer - about 1 mm thick - placed in front of the lens to compensate for the
missing IR cut filter.
This modification worked reasonably well although could not overcome the relatively poor quality of the simple lens to provide high resolution images
in long distance focus.
I was recently sent (for free!) a high quality precision optical grade IR filter that passes infra red wavelength light above 750 nm. This happened to
conveniently fit the front plastic lens cover of the Vivitar camera to give the camera a (quite inappropriate!) high tech IR appearance.
The attached landscape images taken with the IR pass filter attached - edited to black and white to remove the original red colour of the IR images -
gives a sense of what to expect with IR landscape digital photography - dramatic dark skies and evergreen vegetation that is white (note the shrubs
around the door).
The mounds of white stuff on the ground is snow - bad winter this year.
[file]26589[/file] [file]26591[/file] [file]26593[/file] [file]26595[/file] [file]26597[/file] [file]26599[/file] [file]26601[/file]
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jdowning
Oud Junkie
Posts: 3485
Registered: 8-2-2006
Location: Ontario, Canada
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The hidden detail on the test card previously reported on this thread was revealed quite well with near infra red imaging (using the modified Vivitar
digital camera) under reflected daylight illumination.
The test has been repeated this time under transmitted light conditions - that is with the card illuminated from the back and the card photographed
from the front with near IR imaging.
The test card is 0.4 mm thick printed on one side with the print covered by strips of paper and fabric glued in place to obscure the printed detail
under visible wavelength light. For this test the card was placed in front of a desk lamp fitted with a standard 60 watt incandescent light bulb -
incandescent light being rich in IR wavelength light.
The test card is so thick that no visible spectrum light passes through.
The view through the modified camera is a different story, however as is evident in image Fig. 1. The near IR wavelength light passes easily through
the thick card allowing the hidden printed detail on the card to be clearly revealed - a considerable improvement over the images recorded under
reflected IR light conditions.
Taking the test further - to get some idea of the material thickness that near IR wavelength light will penetrate under transmitted illumination
conditions - the test card was clipped to a piece of quarter sawn Sitka Spruce sound board material 2.5 mm thick. The attached image Fig.2 shows that
even with the wood thickness plus the card thickness, the results are still slightly better than the reflected light images previously posted in
revealing the hidden detail on the card (the focus of this image is slightly off so could be improved).
The images have been converted to 'grayscale' to remove the red tint inherent in the IR images.
No doubt, increasing the intensity of the incandescent illumination (i.e. using a higher wattage light bulb) would result in an even greater depth of
penetration of the IR wavelength component? However, higher intensity incandescent light comes with greater heat output that might cause problems when
illuminating heat sensitive materials - so some caution is necessary.
Alternatively low voltage, high intensity, incandescent flashlight lamps (e.g 'Krypton' bulbs) or infra red LED's would be a safer, cooler
alternative.
[file]26796[/file] [file]26798[/file]
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