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Doing my special effects optical work, I often need a densitometer, to check exposures & film densities, but found bying a commercial unit to be far too expensive - and, I didn't want to run to the lab everytime I needed to measure a strip of film!

So, I decided to construct my own - I've always been a tinkerer in electronics. With the help of a friend, Kusti, who is a brilliant programmer, we built most of the functions into software programmed into a HC11 microprocessor chip, so the mechanics are simple: A stepper motor that rotates a tri-color filter between the light source and the film to be measured.

   

Checking the accuracy of this instrument with the help of a commercial unit at a film lab, I was surprised to find that my own unit was accurate to within +- 0.02 D! This is more than enough - Kodak's tolerance for 5244 interpositives is +- 0.10.

Building this densitometer proved that Do-it-Yourself technology really can work! (And that it is nice to have friends who are software geniuses!)

The source code for the densitometer software is available on Kusti's website: www.sparetimelabs.com.


Some time ago I constructed an INTERVALOMETER, a gadget used for triggering a stop-motion movie camera at set intervals. With it, I can shoot growing plants, clouds forming and dissolving, rising and setting sun or moon, people or traffic patterns, etc.

The intervalometer functions are controlled in software, again on a HC11 chip, with 3 pushbuttons; the display always shows the corresponding value (the arrows show how the input mode changes when pressing the "select" button):

I also made a version of the intervalometer with a built-in stop-motion motor for Bolex cameras. It is a crystal controlled stepper motor, and it can be run on both battery and AC adapter power. The system also includes a "breakout box", containing a duplicate of all the controls so that timing adjustments can be made without the risk of accidentally jarring the camera in the middle of a shot. The intervalometer/motor is attached to the Bolex's motor attachment sockets with 3 screws. No modification of the camera is necessary. By attaching the motor so that the camera shutter is left in the "open" position between frame advances, the system can be used for long-exposure time-lapse shooting of night skies, exposure times from 1/2 of a second upwards.

This is one of my first intervalometers - no microprocessors or electronics, it's all electromechanics, back in the early 1970's... You can see the big wooden box with electrically driven clockwork mechanisms, switches and stuff... The Bolex camera has one of my first single-frame motors attached. These gadgets needed mains power - no batteries here!


I do not supply any of these products "ready-made", but have posted the info here for those of you interested in the technology - and perhaps contemplating similar projects yourselves...

Building either or both of these projects is really a major undertaking, quite time-consuming; I did them as "hobby projects", and at the same time explored the possibilities of using a microcontroller instead of older, more "traditional" electronics. Gadgets like these CAN be built using just normal logic gates and even with electromechanics (as you see in my old intervalometer above), but it was more challenging and fun to do it the "hard way" - and get a lot more functionality thanks to the software approach...

Below are block diagrams (i.e. incomplete schematics) I sketched for the electronics in these projects - please note that these are suggestions only, and you would have to finalize your own design, depending on the available components etc. I do NOT provide complete instructions here, nor will I provide any further assistance; if you have the incentive to build electronics, you probably have the knowledge necessary to decipher these notes - I never did draw complete, proper schematics myself... All the necessary information on the components is available in the Data Sheets of the manufacturers of the IC chips. (I've used the Motorola HC11 microprocessor, MC 34160 for power&reset, MC 3479 stepper motor driver; Texas Instruments light-to frequency converter TSL 230; and Hall sensors of type UGN 3020. The spec sheets for these are available on the web, too. It's up to you to decide what other logic components to use; I used mostly CMOS chips for the timing, switching and other extraneous circuitry...)

Complete electronics tools, such as Volt-Ohm-meter, oscilloscope, soldering equipment etc. are needed during construction. You also need to learn how to use the HC11 microprocessor controller, to write and "burn" (i.e. program) the software into it using the serial interface of your PC or Mac.

Densitometer:


If you don't understand what these scribblings represent, then these projects are not for you! ;-)

Intervalometer:

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