Bulb Flash interface

I have been fiddling around with using Flash bulbs with my K5.

However I have no idea how the flash output in a digital camera works.

So I fitted a 10k Ohm resistor in series with the Camera flash socket centre pin and connected + 25V DC to the resistor.
I connected an oscilloscope to the other end ( camera centre pin).
The oscilloscope showed the full 25V.

No current was indicated so far. Then I fired the shutter First in Av Mode with a shutter speed of 1/180 sec
The oscilloscope trace showed about 60mS Low pulse.with 2.5mA current.

I switched to manual and set the speed to 1/30 Sec and again I had a 60mS low pulse.

The figure of 25 volts was used, because most Bulb flash guns use a 15V or 22.5V Battery.

So this is save to use with the K5 output.

However a flash bulb has a very low resistance before firing and because the Capacitor in the flash gun can deliver a very high current momentarily, I assumed this may not be good for the camera.

I then made up the following interface, which fitted in to a 35mm plastic film container.






The components are all readily available.

The main current sink is the IRF540 FET It can sink short term 80 or more amps.

The transistor is a PNP in a plastic case with a current capability of about 1/2 to 1 amp.

The rest is self explanatory. The components are cheap.

You need to check, If the output of the flash gun is positive or negative on the center pin. Both versions are drawn.

The interface works extremely well and the current in to the camera is only momentary with a peak of about 5ma. This is very safe

I used the camera in manual with the highest speed of 1/30 sec with the normal AG an AF flash bulbs.

This gave very nice images. Mich nicer then the electronic flash

If you like this idea and have any more questions. don't hesitate to ask.

Kind regards, Horst