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Authors: Prof. Robin Williams and Gigi Williams

The practical operating "window"

From the previous discussion it is possible to overlay all the spectral transmission or sensitivity curves on a common axis. The result is a harmonization diagram, shown in Figure 52. It demonstrates how the practical window for reflected ultraviolet photography, using conventional films and optics, is from 320nm to 390nm with a peak sensitivity at 365nm. It can be seen that the film is sensitive in this region, the filter and lens both transmit in this region and the xenon flash emits between these wavelengths.

Practical operating window

Figure 52 (above). The 'harmonization' diagram for the system components - lens, filter, light source and film shows that the practical operating window for reflected ultraviolet photography is actually between 320nm and 390nm.

Recommendations for Practical Working Methods (35mm)

Method Reflected Ultraviolet Control
Film T-Max 400 rated at 3200ISO T-Max 100 rated normally
Processing T-Max developer 1:4 0.5mins 24ºC T-Max developer - 8mins 20ºC
Filter 18A None
Lens 105mm Micro Nikkor* 105mm Micro Nikkor
Focus Shift Move the whole camera back by:
1:10  100mm
1:8  47mm
1:4  21mm
1:2  7mm
1:1  4mm
Light Source Studio flash SB-140 Studio flash SB-140
Exposures Variable with power and condition of gold filter however, a general guide is to meter for the visible and give 5 stops more. Full power
1:10  f8
1:8  f8/11
1:4  f11
1:2  f16
1:1  f16
Meter as usual Full power
1:10  f8
1:8  f8/11
1:4  f11
1:2  f16
1:1  f16

* For those with access to an ultraviolet lens this lens is 1.5 stops faster in the ultraviolet and does not require any focus shift.

It is critically important that a standard 'control' image - in colour or panchromatic black-and-white - that represents the visual appearance of the subject, be included as a reference with all scientific invisible radiation records. Obtaining exactly the same viewpoint, with the same lighting can be a very challenging task; this is exacerbated still further when undertaking multi-spectral analysis, where at least three cameras are involved. The authors designed a simple system (Figure 53) where the electronic flash is actually fixed to a tripod and quick release plates fitted to tripod and each camera allow the rapid change over of cameras.

Practical arrangement for multispectral analysis

Figure 53. A practical working arrangement for multispectral analysis. The flash is mounted to the tripod and remains in a constant position whilst cameras are changed easily by utilizing quick release plates.

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© 2002 Prof. Robin Williams and Gigi Williams - Disclaimer
Last modified: 3 May 2002