Tuesday, July 17, 2007

[UV] How to recover a fainted thermo paper receipt

Reflected UV Photography fascinated me since the first time I read about it on http://www.naturfotograf.com/ . But it hasn't been used on landscapes and wonderful flowers only, one of the most important aspects was forgery detection an forensics also. Here is some literature on that http://msp.rmit.edu.au/Article_01/16.html

Today I made some quick tests with an older fainted 2003 thermo receipt from a gas station. My goal was to get back the fainted information on that receipt using my Nikon D70 @ISO200, Nikon SB-140 flash and an UV Rodagon 60mm lens. The idea was to try out reflected UV, UV fluorescence and reflected IR.

1) UV (Baader U-filter, SB-140+SW5UV):

2) UV+IR (no filter, SB-140+SW5UV):

3) UV Fluorescence (Baader UV/IR cut filter, SB-140+SW5UV):

4) IR (B+W 092 filter, SB-140+SW5UV):

In my opinion the reflected UV and UV fluorescence works quite well, but the IR seems to fail.

The good thing is, that for UV fluorescence one doesn't need an UV transmissive lens (like the one I used), but a "normal lens" suffices. All one needs is an UV blocking filter (like the Baader UV/IR cut filter) plus a strong flash which emits UV. One has to be careful to block unwanted IR, since that might render the results useless (cf #4). So ideally one should have an
UV/IR cut filter in front of the camera lens.

More info on this very interesting field may be found on my site http://www.pbase.com/kds315/uv_photos