For contact electrophotography I prefer to use my HVFB generator, the frequency is larger and gives better pictures. (click on the photographs for full detail)
Here... my finger... It was taken with the power supply that runs the HVFB generator at 15 volts. Measured frequency was 54 KHz.
Now see what happens when we increase the voltage that runs the HVFB, from 15 to 30 vdc. Although the frequency falls a little, the discharge is greater!
Here, also taken with the HVFB but now two fingers.
The scale in millimeters will help to have an idea of the physical dimensions of the details seen in the picture.
Did you notice the little dark dots on the crests of the fingerprint? Those are the sweat pores -little openings from where the sweat comes out from our body. Click on the last image and notice the red dots on the right of the picture... what are those things? These dots are false images due to under the film streamers... You see that this methodology has its disadvantages too.
This one is interesting, you'll see a red zone in the lower part of the picture. Again a false image was formed: no red red light was present in that place, never ever, what happened was that below the film the streamers activated the red layer of the color film...
Therefore the red light you see was never there, it's just an artifact, an image generated due to particular conditions. When the film manufacturer designed his film he was never thinking in this particular use (contact methodology), so the film behaves in unexpected ways...
These false images may appear if there's a little air cavity underneath the film. In such places the air may ionize producing luminous discharges that activate the lower layers of the color film.
In this photography the red dot is on the lower left side.
This one is quite interesting...
If instead of using a photographic film we use a THERMAL PAPER, the ones used in fax machines, we obtain the picture shown on the left.
The streamers heat the paper so they may reproduce the path of the discharge... cool! isn't it?
Remember the leaf in the lower right corner in the last photograph? Well, see what happens when we connect the ECT to the High Voltage Capacitive Discharge Generator - ( HVCD ).
Like it? build one and try yourself!
Now let's take a look to my finger... The power supply voltage is lower and I used a high speed film to record the details...
Again I used the HVCD generator, but the frequency is low, only 4 KHz.
Now let's use the High Voltage Flyback Generator - ( HVFB ) , increase the frequency to 40 KHZ and see what happens...
Just fingers? Here you have my right hand. Again with the HVFB @ 34 KHz.