A Simple Photo Scale for Transmitted Light Photography

(This original article was submitted by the author.  While Diane moved from sunny So. California to the colder Indiana climate a couple years ago, she has maintained her SCAFO membership and many friendships with So. Cal. and we hope someday she'll return for more than just a visit.)

by DIANE DONNELLY
Indianapolis--Marion County
Forensic Services Agency

As a Latent Print Examiner and not a photographer by trade, the recording of friction ridge detail posed a challenge for me once I became employed as a Forensic Scientist with the Indianapolis--Marion County Forensic Services Agency (formerly employed by San Diego Police Department).  Quite often I attempt to photograph latent prints on various types of plastic bags using transmitted light via a light box.  The constant challenge was to make the photo scale visible.  Even with adding light focused directly on the scale, it appeared under--exposed in the contact print.

Frustration however, sometimes gives birth to creative and different ways to overcoming obstacles or accomplishing goals, especially in the forensic field.  The solution was so simple I was amazed I had never figured it out before, and neither had other forensic scientists I spoke to.  Hopefully, this information will help some other photographically challenged person(s):

bullet Fill out your photo scale as usual.
bullet Remove the adhesive backing and press the scale firmly on a white sheet of paper. Copier paper works fine.
bullet Place the paper with the photo scale face down on the copier glass (manual copying mode).
bullet Take an overhead transparency sheet and place it on the top of the paper feed.  Some copiers have an automatic by--pass tray, for copying on something other than the standard paper.
bullet Copy as usual.
bullet The scale background will appear clear instead of white, allowing the light to filter through during photography.  The black increment markings will remain unchanged.
bullet Cut out the scale, arrange it on the evidence and photograph the evidence as usual.

Note: You may have to increase the contrast setting to insure that the increment markings do not appear washed out.  Compare the transparency with the original to make sure it is 1:1.  If not, it can be size adjusted on most copiers.

(Editor--—With a fair amount of photographic background and having been plagued with this same problem, I pled guilty to not having heard or thought of this simple solution--—Thanks Diane.  Incidentally I suggested to Kathy Saviers at Lightning Powder that a commercial ruler on a clear substrate would be a good idea. She politely informed me that Lightning has had such a product for about a year. So buy one, or make your own, either way the idea is a great one.)

This article was reprinted in “THE PRINT”
Volume 13(3) May/June 1997, pg 4
and has been obtained from the online library provided by the
Southern California Association of Fingerprint Officers
www.scafo.org