Capturing the Moment: Photographing Low Level Signals from Serological Testing of Swabs and Cartridges. Brittney Gonzalez, M.S.

Transcription

1 Capturing the Moment: Photographing Low Level Signals from Serological Testing of Swabs and Cartridges Brittney Gonzalez, M.S.

2 Mission Combine the knowledge of the Photography department with that of the Serology department Photograph the serological swabs and cartridges that are used and analyzed in the lab everyday Eventually be able to use these images as part of the case record

3 Objectives Find a photography method that allowed the image to be captured within the time constraints of the tests. Find a photography setting that would accurately depict all signal levels. Create an image that would be consistent with the results viewed in person by the analyst.

4 Scientific Approach Conduct an experiment in a methodic and scientific manner Design a method that was practical Has to be used everyday in the lab setting Fit the time constraints of the test Obtain a result that could be easily duplicated Many different analyst will be using this method on many different cases

5 Finding a Method Alternative light source photography: Exposure times exceed the test s time constraints Exposures are usually upwards of seconds per image Cumbersome equipment Traditional ambient light photography: Need a tripod Not enough light for hand held camera use without a flash

6 Finding a Method Traditional Flash Photography: Quick Exposures are limited to a fraction of a second Easy to use Most people are familiar with flash photography Requires minimal equipment Only need the camera, lens and flash

7 Equipment Nikon D5000 Camera ISO 200 Shutter speed: 1/125 th of a second Aperture: f/20 Nikkor 85 mm macro lens Nikon Speedlight SB-900 Flash

8 Hypothesis An image taken with traditional flash photography and proper camera and light settings will produce a timely and effective result. Factors may affect the swabs and cartridges differently.

9 Design an experiment Eliminate one variable at a time Background swabs only White, Gray, Black Exposure Compensation 0.0 through -0.7 (swabs) 0.0 through -2.0 (cartridges) Lighting Angle Direct, 45 deg. angle, 90 deg. angle

10 Exposure Compensation Ranges from a negative to positive value

11 Exposure Compensation Positive values make the subject brighter Negative values make the subject darker

12 Lighting Angle Direct Light at 45 angle Light at 90 angle

13 Scientific Approach Have a Control group Conduct the entire series on a set of dry swabs/blank cartridges Understand the nature of the media Eliminate possible extraneous images.» Eliminated the 45 deg. lighting angle on the cartridges

14 SWAB Control Scientific Approach image LIGHT ANGLE SURFACE number EVEN DIRECT 45 DEG 90 DEG WHITE GRAY BLACK 1 x x x 2 x x x 3 x x x 4 x x x 5 x x x 6 x x x 7 x x x 8 x x x 9 x x x 10 x x x 11 x x x 12 x x x 13 x x x 14 x x x 15 x x x 16 x x x 17 x x x 18 x x x 19 x x x 20 x x x 21 x x x 22 x x x 23 x x x 24 x x x 25 x x x 26 x x x 27 x x x

15 Controls/White Background Direct Lighting

16 Controls/ Black Background Direct Lighting

17 Controls 18% Gray Background Direct Lighting

18 Results: White/Direct & 90

19 Results: Black/Direct & 90

20 Results: 18% Gray/Direct & 90

21 Weak +/ 18% Gray Background/-0.3

22 PSA/ 90 Lighting

23 PSA/ Direct Lighting

24 PSA/ Direct Lighting/-1.67

25 Analyze the data Find a setting that appears to work best Swabs Gray background -0.3 exposure compensation Direct lighting Cartridges exposure compensation Direct lighting

26 Optimal Settings

27 Scientific Approach Test the results Photograph several swabs/cartridges with a varying array of signal strengths at the setting that you have chosen

28 Further Studies Validate the experiment: Compare the results seen in the images to those described by the analysts Be careful to determine what constitutes a positive result Make adjustments to the camera settings if needed Create a sample set large enough to have statistical significance

29 Impact to Forensic Science Permanent record of the results Images can stay with case folder Images can be compared with the written description given by the analyst Can possibly be used in judicial proceedings if necessary

30 Special Thanks Harris County, Francesca Daher, B.A. Tiffany St. Rose, B.S. Dr. Roger Kahn Michael Donley, M.S.