jimtrue.com : school : CJT1221 : 2003-05-30: Advanced Forensic Photography

Posted by Jim True on May 30, 2003 6:32 AM. Last Updated October 22, 2006 9:23 PM

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2003-05-30: Advanced Forensic Photography

Where are we going?

• Camera basics - a refresher

Nikon 6000 or Nikon 6006

• Photographic Techniques
• Lighting
• Filters
• The Darkroom
• Film Development
• Print Development
• the Digital Darkroom

How Does Film work?

The emulsion is made up of millions of silver salt crystals (called silver halides). When the film is exposed to light (as the picture is being taken) these crystals break down into black silver.

How is Film Designed

Black and white film is made up of a chemical mixture (called an "emulsion") protected by a thin plastic layer. In color film, the emulsionn is made up of layers sensitive to blue, green, and red light. When you take a picture, the film's chemical coating is exposed to the light.

Everything we see on the film will be exactly the opposite of what we will see on our final print.

When film is developed, the chemistry works with the silver halides; the more light they are exposed to, the less the chemical reacts to halides on the negative and the less of an emulsion layer will be on the film.

Black and White film: Scratch-resistant coating, two layers of scratch resistant coating, with an emulsion. In color, the emulsions are layers that are sensitive to blue, green and red.

Kodak T-Grain Emulsion Crystals

Will not use in this class. Need sharp-edged emulsion for sharp-edged resolution and sharp contrast for minutiae in a fingerprint photograph, toolmarks, tire-tracks or shoeprints.

Films

• Panchromatic films (T-MAX, Plus-X) are blue, green and red sensitive. Colors are shown in varying shades of gray. Because they are panchromatic, they work well with contrast filters.
• Orthochromatic films (KODALITH) are blue and green sensitive only. Red will appear black in a black and white print.

Speed of light - 186,000 miles per second

Color is either transmitted, reflected or absorbed. In Forensics, we do a lot of work with Alternate Light Sources (luma lite, UV Lamp). How the light rays react to evidence, allows us to see varying colors differently than under white light. 400-700 nanometers is the range of visible light.

One micron is roughly the width of a strand of hair. 1000 nanometers is equal to one micron. Using this analogy, the range of colors we can see in visible light is less than the width of a human hair.

When the use of alternate light sources became regular method, the amount of trace evidence collected quadrupled. Pinellas was the first agency to have a YAG laser, pulsating green light. Transmitting a specific wavelength, it will either reflect or absorb when it hits a piece of evidence. Stoke's shift is the principle we work with when using Alternate Light Sources. Since light is energy, when energy is absorbed or reflected, this reaction will cause a color change. We can take green, yellowish-green or blue light, if it is absorbed by that piece of evidence it will change color, because it will lose energy. So we take a pair of goggles that are orange in color (50 nanometer range), blocks out any colors above green, so the color changes will be above the orange color and will be able to see this red, lower energy light being transmitted from the evidence.

With the cameras we will be absorbing that light with our cameras, and contrast filters to change how the camera captures light on the negative.

How Does film Work?

• When unexposed film is exposed to light metallic silver forms in areas of the film that were exposed to light.

Clear on the negative, will be black on the print.

• The more light, the more particles form.
• The resulting image is called a negative.
• On a negative, the lights tonal values are reversed from the actual image.
• These reversed tonal values are reversed again when projected onto photographic paper during the enlarging process. Basically, the enlarger is a reversed camera.
• The Resulting photograph is an exact representation of the original image. when it isn't, you've made a mistake in depth of field, focusing, etc.

We create depth by using shadows, shadows in the tire tracks with an oblique light is an example.

Train your eyes to see like a camera sees; makes the difference between a picture taker and a photographer.

Temperature Control

Film development is temperature critical.

• Repeated results are a matter of accurate control of both temperature and time.

If you don't have your chemistry at the right temperature, you will not get a repeatable result. Extremely dynamic.

• Developer that is too warm will overdevelop film.
• Developer that is too cool will underexpose film.
• Optimum temperature for most B&W film is 68 degrees.

When Light Hits an Object

• The waves can be reflected or scattered off the object.
• The waves can be absorbed by the object.
• The waves can be refracted through the object.

Interface is the layer where the air and water comes together before the refraction occurs.

• The waves can pass through the object with no effect.

The Law of Reflection

"the angle of incidence equals the angle of reflection."

Additive Colors

Cyan, Magenta and Yellow

Subtractive Colors

Taking the additive colors to remove a certain color or go to black.

Ansel Adams is the father of nature photography; Clyde Butcher has taken on that role and added to the process.

Black and White Contrast Filters

White light is made up of a mixture of red, green and blue (primaries). In theory, red, green and blue light sources simultaneously projected on the same area will be white. Red and Green mixed together makes yellow. Green and Blue Light mixed is Cyan. Blue and Red Light mixed is magenta.

Contrast filters for blood spatters - red filters.

Red walls, you would have to stain the blood to make it visible. CSI and others will say they will use an alternate light source to make blood visible. Blood absorbs ALS; it does not luminesce. ALS designed to pick up trace evidence and other biological evidence. Blood would show up as black.

Film Processing Chemicals

• Developer
• Film - D76
• Paper - Dektol

Developer acts chemically upon the silver halide crystals reacted on the film. Will clear away any crystals not reacted upon by the light. Just the oppositie will light sensitive paper.

• Stop Bath

Acid that stops the chemical process from working with the developer. Much more critical to film than paper.

• Fixer

Fixes the process at that point so it goes no further.

• Wash

Critical in film to get the chemistry OFF the film so it doesn't make it foggy. Add a couple of drops after the wash of a chemical called PhotoFlo; emulsifier - helps the water shed itself off the film. Spot-free drying (just like Jet Dry in the dish washer).

Multiple prints from a negative; only one chance with developing the film.

Developer

• D-76 Film Developer
• Dilution 1-1 for fine detailed negatives.
• Straight slightly less fine but recyclable.
• Dektol Paper Developer
• dilute 1-2 and do not keep

Stop Bath

• Used to neutrailze the developer solution that remains on the film after the development time has elapsed.
• Dilution 1-32 or a cap full to a tray of water.

Fixer

• Used to dissolve any remaining light sensitive silver from the processed film or paper
• Dilution 1-4

Developing

From the Book, picture of cans, spool, etc. pg.9

metal style and plastic self-load. We use the plastic self-load in the school; can stain and can have chemistry adhere to the spool. Metals are easier to clean but harder to load.

Tanks, reels, chemicals, timer and thermometer.

Light and air-tight bottles for the chemistry.

Wetting agent is the photoflo

When drying the film, you want to have a little bit of weight; keeps the film straight as it dries.

Developer

Factors affecting final results: Film Speed and Developer Temperature

How to get all the chemistry the same temperature - use a water bath, a bucket, all the chemistry containers in the bucket with water all at the same temperature until they equalize. Water should be cooler than the range of temperature you're looking for.

Let's make it dark to see what develops. pg 14

Can opener to open film canisters. Scissors to remove leader and the tape on the center spool piece. Tanks and reels.

Film Development Procedures

1. Load Film in complete darkness
2. Start timer and add developer to tank - somewhere around 8 minutes. Start the timer before you add the developer.
3. Agitate the tank for first minute and then every 30 seconds, you give it two inverts until developing time is elapsed. Gentle inverting of the tank and back; no shaking as this develops bubbles.
4. Time is 5 1/2 to 6 minutes; closer to 8 minutes.
5. With 5 seconds to go in the developing time, pour developer out and add stop bath, agitate for 30 seconds and pour out and discard. Rather see us go a minute with the stop bath to make sure the chemistry is off the film.
6. Add fixer, agitate for first minute and then every 30 seconds for twice the developing time. 8 minutes, go to 16 minutes.
7. After fixing time has elapsed, pour out the fixer and wash with running water. Continual clearing of the water just to make sure all the chemistry is off the film.
8. Time for washing is 10-12 minutes.
9. After wash add 2 drops of Photo-flo to a tank of water and add film.
10. Agitate for 5 seconds and then let stand for 30 seconds.
11. Hang until dry. Use fingers as a squeegee to remove as much water as possible off the film.

How did you do that?

Photograph of the enlarger, p 31. Inverted camera.

Most of our exercizes will be producing scale photographs. Save some containers (bottled water), things that might be interesting to photograph. Put a fingerprint on it and dust up a print. Evidentiary value.

"Cadywampus" - means it's not straight on the enlarger

If you hold this tight, the results will be just right

Negative Carrier - 4 locking pins are designed to hold the negative perfectly in the center. Hinge on the back to allow the top half to flip up and place the negative in place.

Paper Types

• Resin Coated Paper

Impregnated with light sensitive chemicals

• Fast rinsing
• No curling prior to mounting
• Fast Drying time
• Fiber Based Paper
• Prior to resin coated papers
• 1-2 hour wash
• curling after drying
• Drying times after many times longer than resin coated

Paper Grades

• Multi-grade or fixed grade

We're using multi-grade paper

100 pack of multi-grade paper is about $40 bucks

when using filters, have to increase the paper exposure time

• Grades from 0-5; can create same grades with multi-grade with filters. Multi-grades are basically grade 3

Paper finishes

• Glossy - primarily what we use for contrast and sharpness.
• Semi-gloss
• Matte
• Semi-Matte
• Pearl
• Canvas - good for people portrait work

Print Developing

• Exposed paper is placed into the developer exposed side down and then tray is gently agitated to guarantee that solution is covering print uniformly.
• After one minute, turn paper over and continue to agitate for an additional minute. Gently lift a corner of the tray so there is a gentle waving motion, not sloshing.

You can overdevelop film, but you cannot overdevelop paper.

• After the two minute developing time has expired gently remove the print, allow it to drop and then place it into the stop bath face down for 30 seconds to a minute.
• After the time has elapsed in the stop bath, gently remove the print from the stop bath and allow to drip before gently placing into the fixer face down.
• Fix print for 3 minutes

Each step has agitation. Can place more than one print in the chemistry at the same time, but they must be added at the same time so that you don't confuse the time values.

• Once the fixing process is complete, carefully remove print. Allow to drip and then place in rinse for 5 to 10 minutes.
• After wash is complete hang to dry. DO NOT USE A PAPER TOWEL or you will mar the surface of the print.

Close Up Photography Lighting Techniques

Lighting techniques are a little different from photo one, because we're dealing with different surfaces and more close-up photography.

1. Axial Lighting - most unique form of lighting, just started using in the last year. Predominately, subject is on the base, light comes in at 90 degrees and have a glass plate. Used to light up the inside of the object [like a film container with a drop of blood inside] (how to get the light inside the object and still get a picture). Camera can see through the glass, light reflects off the glass axially into the film container.
2. Bounced Lighting - works extremely well on items that are extremely reflective in nature. Bounce the light up into a domed device onto the reflective surface and take away the glare. Surfaces with lot of reflectivity, glass, mirrors, chrome bumpers, door knobs, shiny surfaces.
3. Diffused Lighting - Much easier to work with than bounced lighting. Can be as simple as taking a gallon milk jug, hole at the top for the camera, light shining through the jug to create milky white diffused lighting. Works with flash, regular lighting and with flashlight. Same concept as above but easier and softer light.
4. Direct Lighting - what you see on the copy stands right now, two lights from both sides of the object to remove shadows. Used in most cases for surfaces that are flat that don't reflect light. Paper items as an example. Need to eliminate shadow, don't have to worry about reflectiveness. Latent prints on paper in nature, ducttape, cardboard.
5. Direct reflected lighting - light is in closer to the camera. Trying to light something that is sitting slightly above the surface. Very seldom used. May need a little bit of shadow to help see the item.
6. Oblique Lighting - light normally at 20 degrees or less to create drastic shadow. Raised image (shoe prints, shoe tracks, tire tracks, tool marks) - creates depth with shadow and three dimensional look. Without shadow you have no depth.
7. Transmitted lighting - some sort of evidence, predominately fingerprints on a glass item. Light would come from behind the glass to illuminate and create contrast for the fingerprint.

One to One Photograph

• No Scale needed - creating a photograph at same size as the item photographing - fingerprint.
• Camera lens is set to 1-1 setting and the camera is moved up and down to focus.
• Printing of the image is a contact print. Negative is directly on the photographic paper; no enlarging - negative image is EXACTLY the same size as the actual item. One to One.

Same concept as a 'Proof Sheet'

Scale Photography

• Scale needed for size re-production; used to reproduce an exact size reproduction in the darkroom.
• Lens is focused normally. Compose to fill the frame as best as possible.
• Printing is done using enlarger and matching scale in photograph to scale on enlarging easel.

Used for Scale photograph of shoe tracks, tire impressions, etc. Make sure the scale or scale item matches during the enlarging.

CAMERA FILM PLANE MUST BE PARALLEL TO THE SUBJECT YOU'RE PHOTOGRAPHING. You cannot enlarge to scale properly or perform your contact print properly.

Need a bubble level for the ground and transfer that measurement to the tripod to make it match

Photographic Requirements

• Camera and subject must be parallel to each other (film plane to subject).
• Depth of Field must be as great as possible (F8 at least, F11 and F16 if possible). Closer you get to the subject, field of focus becomes less and less and less.
• Copy stand or tripod IS required.

Determining Correct Print Exposure

• Test Print - shows ALL possible exposure times to get the best contrast and exposure.
• Choose contrast filter that will help create the best contrast between the subject of the photograph and the background (photo)
• Choose the correct grade of paper to support the negative and the subject.
• WE MUST BE ABLE TO CAPTURE THE SUBJECT WITH GOOD CONTRAST AND CLARITY IN FORENSIC PHOTOGRAPHY

Test Print

Assume F8 at 5 seconds. Place the paper in the easel, take a piece of good hard cardboard. Make a 5 second exposure across the entire piece of paper. then I cover up all but one strip, take another 5 second exposure, then 2 strips and another 5 second exposure. Keep going until you have a test print of 5 seconds to 35 seconds - which is the best exposure for this print.

Final Print - 25 seconds at F8

Disclaimer: These are MY notes taken from classroom lectures while I'm in the classroom. While I'm perfectly happy to share my notes with my classmates and I know I take very good notes, you should still make every effort to attend the class and TAKE YOUR OWN NOTES. I will not transcribe everything the instructor says in the classroom, and I will NEVER post pre-exam reviews. My notes will not replace the value of actually attending class and taking your own class notes.I also cannot attest to their accuracy, other than they are what was provided in the lecture; you should not reference my notes as "expert opionion" by any means, and if you notice an error or omission, please do me the favor of e-mailing me with the correction and I will re-post my notes. End of Disclaimer.