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How to hack an auto thyristor flash for manual settings?

I have several cheap Vivitar 2000 non-dedicated flash units which have an auto thyristor but no manual settings.

Since the auto thyristor does exactly what i would like to do manually (i.e. dump excess voltage) i would think it shouldn't be too difficult.

I would love it if someone were able to tell me how to hack this unit to manually be set to lower light levels. The most obvious problem might be that there are three settings set by a switch on the back of the flash. red M and green. Red and green presumably control the sensitivity of the auto thyristor.

The other is that specific settings, (i.e. full, 1/2, 1/4, 1/8, 1/16, 1/32 or f-stop settings full -.5, -1, -1.5, -2, -2.5 -3, -3.5, -4, -4.5, -5, -5.5, -6 f-stops ) be available. problem would be that that i dont think flash output is linear (i know it's not for stops)

Anyone up to the task?

Ben
Sat, 10 Mar 2007 13:16:14 -0800

The red a green mode affect the photo sensor by physically moving neutral density filters over the 'window' in the flash and in any electrical way. This means that the solution to this should be easy.

Could one simply place calibration marks around the radius of a a logarithmic pot using a flash meter?

Ben
Mon, 19 Mar 2007 21:26:06 -0800

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