Monday, March 28, 2011

High Speed Sync Hack For LP160


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.

Progress & Summary: 

From LumoPro's LP160 website, the LP160 flash durations for  t.1 and t.5 are: 
Fullt.5 : 1/1200t.1 : 1/450
1/2t.5 : 1/1300t.1 : 1/950
1/4t.5 : 1/2650t.1 : 1/2250
1/8t.5 : 1/4750t.1 : 1/3700
1/16t.5 : 1/9100t.1 : 1/6050
1/32t.5 : 1/18200t.1 : 1/9450
1/64t.5 : 1/27800t.1 : 1/13150

The External Method:
The idea I had for an external means of enabling HSS/FP-sync was to strobe the flash at a high rate of fire. However, this requires that the recharge and flash duration to be very short, so that multiple flashes can be achieved in the window of time for a given shutter speed. The capacitor also needs enough charge to fire off multiple bursts. 
This basically excludes full and 1/2 power. 1/4 power might be doable with a set of REALLY fresh batteries. But the greatest amount of success would be with using 1/64th power and strobing that at high speed. 
From my napkin estimates, using 1/64th power, one would be able to HSS/FP-sync at up to 1/1000th of a second fairly reliably. Need to test this out. There is a risk that this can damage the capacitor, trigger coil, flash tube, etc. However, it will give you HSS capabilities.

The Internal Method:

This method involves getting into the guts of the flash unit and bypassing the unit's PIC MCU triggering of the flash tube and the cutoff of the power to tube in rapid succession. This is more involved and potentially riskier, as done improperly, can result in high voltages finding their way back to the more sensitive components and risk burning out... well, your flash.

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