ALS Documentation

[Mike Heintzman]

Does anyone know of an agency that requires documentation of the ALS wavelength used in screening for latents after a dye stain application? My own opinion is that it normally varies so much because of substrate interference that it's really useless information (do you record all of the wavelengths used in screening, which ones cause the most fluorescence with a given color of goggle, which ones you use when imaging, etc) and since the test is whether or not there is a latent print on a particular object, not whether or not a particular dye stain fluoresces at a particular wavelength.
Has anybody else had this discussion in their agency?

[Jan LeMay]

I think it's important for reproducibility to document that in my notes. But I don't bother to mention it in reports. Most people reading my reports would have no idea what I was talking about anyway.

[Kathy Saviers]

I thought of the reproducibility aspect also and it might be appropriate for the case notes, but then, again does anyone really NEED that information? If it seems to be that important, then everyone should also note the brand of fingerprint powder and the brand of fingerprint brush they used, along with the number of passes made with the brush to develop the latent print.

While all this is information regarding the development of the latent print, it is useless information.

Kathy

[Guest]

I think it's important for reproducibility to document that in my notes.

Jan,

I'm curious. Do you right down every wavelength and goggle combination that you viewed the item under? Or are you more general?

Thanks,

Mike French
mike.french@metrokc.gov

[Guest]

Jan,

I mean do you "write"? Obviously I cannot be trusted with a pencil and paper.

Regards,

Mike

[Jan LeMay]

I just note the combination that gave the best result which I used to photograph the print. Example: "Ardrox/450nm/yellow filter".

[Guest]

Thanks, that's how I do it too. How about for screening? If you did not observe latent prints do you list all the wavelengths and filters in your notes. My documentation varies depending on what I am looking for.

Mike

[Dan Connell]

I agree with Kathy Saviers. Many times I fine tune to find the best contrast in order to photo a latent print. No one would understand my bench notes anyway. Questions-do you photo in color or black & white? Do you use film or digital.

[Mike French]

The short answer is this: both color and black and white will work. So will a digital camera. I use a 35 mm camera and both color and black and white film. The negatives are later scanned with a high speed film scanner.

The long answer follows....

C-41 color, C-41 BW, silver halide, filtered CCD, unfiltered cooled CCD (grayscale), all could have benefits and drawbacks based on cost, efficiency, and effectiveness. The only thing I consider not debatable in fluorescence photography is the need for the right cut-off filter. Yet there are some who will debate that also.

It boils down to several key points of spectral sensitivity, cut-off filters, noise, and cost.

The first question is whether the media is responsive to the wavelength being emitted?

Example: Sometimes examiners will attempt color photography without knowing how responsive their film is in the bandwidth they are trying to capture. There are many color films that fizzle in the upper end of red spectrum. If you are using a deep red cut-off filter with this film on a fluorescing fingerprint it will be a serious problem.

Look up the spectral responsiveness of your film and do some tests. I use Illford Super XP2 in those red situations with great results. This film is also easy and inexpensive for my photo lab to develop. These images are essentially monochrome due to the narrow bandwidth hitting the film so I don’t worry about missing out on potential color isolation in Photoshop. The key with this type of shot is to record the intensity rather than expecting any significant color variation.

If you select digital capture, long exposures with a CCD will introduce noise. Using a camera with a cooled CCD or a more sensitive unfiltered (grayscale) CCD can minimize this. But few departments have the bucks to pay for one of these specialized cameras. I am not trying to dissuade folks from using a digital camera but I would suggest doing whatever you can to get your fluorescing image as bright as possible before releasing the shutter.

And then we get to the question of whether we should be using a filter at all? I understand this debate in general photography, but fluorescence photography? That would be like trying to see the stars at midday. There are Photoshop instructors promoting this. Not photographers though… dodge and burn will only go so far.

Regards,

Mike