Lighting Fire Scenes for Digital Cameras

Yesterday I was in Beverly Hills doing a fire scene with an experienced fire investigator. It was a house where a fire started below the ground floor. The fireman tore up the floor in various rooms and removed sheetrock as usual and dumped it outside.

The scene was a confusion of possible causes. The house had workman in it doing staining of the kitchen cabinets, there was a mass of electrical wires at the area of origin, and after seeing the fire department photos BEFORE it was overhauled we had some very nice inverted-V pattern suggesting liquid flammables.

In any case, it was the usual mess of trying to take pictures in a deep space with a flash. A flash's light falls over with the square of the distance from the flash. This means that doubling the distance decreased the light power to 1/4. Dark deep spaces look like caves in the images.

The thing to do is to turn off the flash. Preferrably lean the camera, brace it, against some wall or door frame or,k even better, use a tripod. The exposure takes longer to happen, but the results are considerably better.

I intend to do a study on this for fire scenes to give some quick rules of thumb to make it easier for insurance adjustors, fire investigators, expert witnesses and forensic engineers to get some good images. Also the trade offs in various lighting techniques.

Derek Geer
Forensic Engineer
San Diego, California
www.geers.com`

Fire Investigation and Camera Lenses

I was on a scene in Moreno Valley off CA-60 and there were three fire investigators and me. (Of course, being the only forensic engineer on the scene I got ribbed for everything. )

However, I did notice that everyone was shooting their cameras while the investigators were shoveling and sweeping debris around. It was probably the worst environment for a camera excluding dipping in liquid acid. The lenses were getting coated with ash and dust.

The usual answer I hear from camera users is: "Oh, I just wipe it off later." Wiping the lens when it is coated with ash and dust is like running fine sandpaper over the lens. It will degrade more and more with each cleaning.

Camera lenses are meant to bend light. But not all colors of light bend the same amount. Early lens designers saw this as creating unwanted rainbow effects around light sources in their images. Modern lenses compensate for this by applying lens coatings. These are very thin coatings on the lens that affect diferent colors of light to bend different in the coating. The result is that the lens coatings compensate for the fact that light colors all bend diferently. If these coatings get damaged, the lens is ruined. But it is not an easy thing to observe.

I use a UV filter or Sky Filter over my lens to protect it from the dust. If that gets ruined, it is only a few dollars to replace.

But if I am shooting in a clean, fairly dust and droplet free environment, then I take off the filter as it degrades image quality slightly (the more glass between your subject and the film, the more distortion and diffusion that can take place).

I will cover lens cleaning procedure in another post--that's a whole story in itself!

Derek Geer
Forensic Engineer
San Diego, California
www.geers.com

Fire Scene Investigation in the dark--Out of focus images

When working burned out rooms and building with practically no light, your camera may create out of focus images. This is embarrassing for court testimony or forensic reports or fire investigation reports.
If your images are out of focus it is probably because there is not enough light for the camera to focus and it is guessing. One easy solution is to light the area you want to be in focus with your fashlight, and then shoot the camera. It will find enough light then to focus.
There is another reason that it may be fuzzy: the camera is keeping the shutter open long enough to catch all the light needed to make an image. Camera shake or movement will then blur. This should be noticably diferent than out of focus, and will only happen when the flash is not going off (not engaged or not turned on).

Derek Geer
Forensic Engineer
San Diego, California
www.geers.com

Digital Photography: What's a pixel?

Forensic Engineers, Fire Investigators and Insurance Adjustors have all converted to digital photography. But what the heck is a pixel?

A pixel is a "picture element"! That's all.
Why is a pixel? Because digital electronics can only understand individual pieces of information. It constructs an image using really small pieces (pixels), which usually look like little squares on your computer screen if you can zoom in really close.
Camera resolution means how many pieces is the camera using. The more pieces, the more detail.
So, is more pixels always better? No! Why? Because there are good pixels and bad pixels. Bad pxels are those that don't show that part of the picture very accurately. So, it is better to have accurate pixels (once you have about 2 megapixels) than it is to have more pixels that are not accurate.
I will be posting some examples to make this clearer!

Derek Geer
Forensic Engineer
San Diego, California
www.geers.com

Photos From Loss Scene

I have decided to help fellow forensic engineers and fire investigators in getting their problem photos enhanced. Future blog items will include ways to do this to get one's point across.

Derek Geer
Forensic Engineer
San Diego, California
www.geers.com