Saturday, April 9, 2011

Fun With Python and Capacitance Values

In line with my work in modifying my flash unit, I was wondering how much capacitance I could get out of a home made paper foil roll capacitor.

As a goal size, I used a typical soda can:
  • 1.31" (33.274mm) x 4.75"(120.65mm)
For the materials, I'm considering standard kitchen aluminum foil and normal printer paper with the following assumptions about thickness/etc:
  • Aluminum foil assumed to be 0.025 mm in thickness (air/water impermeable)
  • Paper thickness estimated to be 0.10 mm in thickness (rounded up from 0.097)
  • Resulting Layer thickness = 0.25 mm (2 layers of foil + 2 layers of paper)
Running the calculation, assuming concentric layers of diminishing size until the can is filled:
  • ~133 layers
  • ~1691201 mm^2 in surface area
  • ~449 uF in capacitance (estimated with K=0.30)
That's a good chunk of capacitance, especially considering that paper's breakdown voltage is 200V per mil:
  • 1 mils = 0.0254 millimeters
  • 0.10 mm = 3.937 mils
  • ~787V breakdown voltage
So.. a capacitor that can safely handle 700V with a capacitance of 400uF.

If I can reduce the thickness of each layer and of the insulator layer, I can bump the capacitance to 2200uF!! Wild. But it would be rather big and clunky. ^_^;;

In either case, solving little problems like this is also a great way of learning a language like Python.


Monday, March 28, 2011

Remote Power and Zoom Control and Readouts For LP160

Goal:

  • To add remote power and zoom level controls to LP160
  • To add remote power and zoom status readouts to LP160
  • To design and implement hardware and software interface to the LP160

High Speed Sync Hack For LP160

Goal:

The goal of a high speed sync hack is to give the LP160 the ability to sync the flash with cameras using shutter speeds of 1/250th of a second or faster, say... 1/2000th of a second. Various companies call this by different names: hss, fp-sync, etc.  It all amounts to the same thing: instead of one single high power pulse, the flash is strobed at high speed, but at lower intensity.

Why? At shutter speeds below 1/250th of a second, the sensor is completely exposed for a brief period of time, allowing a single short duration pulse to illuminate the scene and then expose the sensor. For faster shutter speeds, this doesn't work, because the second curtain of the shutter starts covering up the sensor again before the whole sensor is exposed... this leaves the black bar at one end of the frame. 
To work around this, you expand the duration of the flash by pulsing it, thus exposing for the entire window and avoiding a black bar edge.

Taking Apart The LP160

So, I've been poking and prodding at the LP160 to figure out the best way to build mods for the flash. In doing so, I get to see the underlying guys and figure out what all is in the flash unit!