How to 'slow down' closing of circuit (flashgun)


I got a old camera that has a bulb flash (the old one use bulbs). I want to hack a modern flash into the old case...

Problem - modern flash units/guns, flash too quickly for the older cameras. When the circuit is closed how can i hold/delay the circuit and stop the flash firing too soon.

THanks in advance

Easy: Attach the input from the camera (the contacts on the hotshoe will just be closed) to a timer (eg NE555) or a delaying resistor/capacitor circuit and have then your flashgun triggered. You will need a circuit to drive your modern flash, but those can be found.

Not so easy: Finding the proper delay time. As your old camera most likely has a flash-sync speed of 1/60 or 1/100 second you could start out with 5-10 ms and go from there. If you're camera still uses film, expect to waste a roll on test shots to find the proper delay.


Thanks Korman,

you mention a delaying resistor, can you be more specific please.. i thought resistor just resisted not 'held' , i had thought of a tiny capacitor but was not sure where to start looking..
thanks again

You might have more luck searching for "X Sync" plus your camera name. M bulbs typically took 20ms to reach peak brightness, while xenon is instantaneous. It's probably more mechanical than electrical, let alone electronic.

X sync would be for electronic flash, and fires the moment the shutter is triggered. M sync (magnesium) is for flashbulbs, prior to electronic flash, and the physical shutter opening is delayed 20ms from the act of tripping the shutter and the subsequent immediate triggering of the flash.

Here's an example of the sort of lens that would have both settings:

In other words, it is the shutter opening that needs delaying, not the flash firing. The flash has to fire slightly before you take the picture!