The Long Trek Towards Accurrate Denisty Readings

This post represents the start in my long journey towards building my own combined transmission and reflection densitometer.  Believe it or not, it has been a long-standing (several years) goal of mine to be able to accurately measure the density of metallic silver in my black and white photographic negatives and my black and white photographic prints.  Why, you ask, might anyone want to do this?  Well, I guess I'm just a guy who likes to know how dense his film is.  Seriously, though, aside from the fact that understanding density is crucial to fine tuning one's basic photographic printing technique, it is also necessary for anyone interested in developing their own specialized approaches, such as, platinum printing or creating their own photographic emulsions.

Currently, I am still at the design and planning stage of this project.  This blog is intended to document how I build the densitometer as the project progresses.  Consequently, this first post as an introduction and review of what I've done thus far.

Over the past few weeks I have been reading anything I can find online about densitometry techniques. This includes classroom lectures, lab exercise instructions, documentary websites, and expired patents.  Based upon the documents I have reviewed thus far, my plans for the densitometer can be broken down into a controlled light source, a sensor for reading light from the light source, several possible types of electronic circuits designed to interpret the signal from the sensor and express it as density, and a method of visually displaying the density in a way that humans can understand.  For the controlled light source, I've pretty much settled on using separate sets of voltage controlled LEDs for the reflection and transmission portions of the densitometer.  As stated previously, my goal is to make the densitometer capable of measuring both reflected and transmitted light, so, consequently, it will need a source that emanates from a direction underneath a negative (for transmission) and another source that emanates from a direction above a photographic print (reflection).

Transmission (left) and reflection (right) require light sources in two different locations. 

For the sensor, I've thus far settled on either a photoresistor, a phototransistor, or a photodiode.  I am still comparing the pros and cons of each sensor type and will likely build prototypes with all three and see which works best.

Because it is spring and the weather is getting warmer, I anticipate that I will focus less on this project as I spend more time pursuing gardening, photography, hiking, pottery, geology, paleontology and all the other things I like to do outdoors.  However, I may work on it during the summer from time to time and will no doubt return to this project with greater focus in autumn.