Electronic replacement for AG1 bulbs?

[Chan Tran]

I skimmed through the posts but did not read them all in detail. Therefore, I apologize if my comments have already been covered.

There are at least two technical issues to deal with that relate to synchronization. First, for flash bulbs there is (I believe) a delay between triggering of the flash and opening of the shutter. This is because for flash bulbs it takes some time between the trigger and the main part of the light output. With electronic flash the delay is short and can be treated as if it were instantaneous.

The second is that flash bulbs emit light over a rather extended amount of time whereas electronic flash emits light over a very short amount of time which can be treated as if it were instantaneous.

In principle it is possible to design electronic circuits that will compensate for both of those effects. In fact, the second is already implemented in some commercially available electronic flash units. In some products it is called FP synchronization, and it works by dividing the total output into a series of repeated flashes, each of lower power.

This extended flash duration is mainly useful for cameras that use a focal plane shutter. For cameras that use a leaf shutter, or for focal plane shutters at low shutter speeds, it is sufficient to just compensate for the first effect, i.e. to introduce a delay between trigger and the beginning of light output.

There are, of course, also some other technical issues to deal with.

You need a delay to make sure the shutter fully open before firing the flash. Short flash duration is no problem there is no need to lengthen it.

 

[alanrockwood]

You need a delay to make sure the shutter fully open before firing the flash. Short flash duration is no problem there is no need to lengthen it.

I agree with both points, up to a point. In fact, I believe I mentioned both. An instantaneous flash is fine for a leaf shutter camera, but only works at low speed for a focal plane shutter, that is unless you are satisfied with only a thin strip of the film area being exposed.

 

[Chan Tran]

Sure but nobody is asking to sync at high shutter speed. The OP only wanted to use an electronic flash instead of flash bulb.

 

[alanrockwood]

Sure but nobody is asking to sync at high shutter speed. The OP only wanted to use an electronic flash instead of flash bulb.

Hmmmm. Sorry. I must have misunderstood. Could you quote the part of the OP where he said what type of shutter he is using, or that he is only wants to sync at low shutter speeds? I must have missed that part of his post.

But regardless, other people who read the thread might be interested in sync for a focal plane shutter at high speed, so I figure the information I provided is still relevant to the topic of the thread.

 

[wombat2go]

The basis of this mod to an old Graflite was to remove the flash socket and machine a brass slug to replace it
The slug is mounted in the head using the original fasteners and has a claw to replicate the hotshoe for a small old electronic flash.
The batteries in the Graflite are no longer required and are removed and jumpered.
The oscilloscope trace shows the flash firing about 1 millisecond after the shutter is open. ( the background illumination was from a tungsten lamp to show the shutter opening).

 

[stressed61614]

AgX,

You're right. I am thinking that maybe I could mount a small electronic flash on a mount and run a couple of wires to the contacts in the camera's bulb holder. Then the current from the camera would provide the signal for the electronic flash to flash. In other words, the current from the camera would bridge the two contacts on the flash (I'm talking a real simple Sunpak flash). The flash will flash if those two contacts are bridged with a wire. Will the current from the camera do the same thing? Proof of concept will be to jimmy a suitable AG1 socket plug similar to the AG1 bulb base and long enough to reach from the recesed bulb hole and then press the camera shutter with wires contacting the two terminals on the flash. Weekend project!

You would have to measure the output voltage of the flash to make sure that it not going to take out your electronic flash. I had the same idea but need a scope to measure the peek output DC voltage. If the flash has its own battery then the camera is (generally) acts like a switch no voltage or very little. The main problem is if you want to make your own LED to replace say 'flash bulb AG1' finding LEDS that can put out the same amount of light Illuminance.

 

[stressed61614]

I skimmed through the posts but did not read them all in detail. Therefore, I apologize if my comments have already been covered.

There are at least two technical issues to deal with that relate to synchronization. First, for flash bulbs there is (I believe) a delay between triggering of the flash and opening of the shutter. This is because for flash bulbs it takes some time between the trigger and the main part of the light output. With electronic flash the delay is short and can be treated as if it were instantaneous.

The second is that flash bulbs emit light over a rather extended amount of time whereas electronic flash emits light over a very short amount of time which can be treated as if it were instantaneous.

In principle it is possible to design electronic circuits that will compensate for both of those effects. In fact, the second is already implemented in some commercially available electronic flash units. In some products it is called FP synchronization, and it works by dividing the total output into a series of repeated flashes, each of lower power.

This extended flash duration is mainly useful for cameras that use a focal plane shutter. For cameras that use a leaf shutter, or for focal plane shutters at low shutter speeds, it is sufficient to just compensate for the first effect, i.e. to introduce a delay between trigger and the beginning of light output.

There are, of course, also some other technical issues to deal with.

You also flash is generally used at a shutter speed of 1/60 of a second. Most bulbs have a different color balance compared to electronic flash or LEDs. Bulbs also have a limited range compared to electronic flash or LEDs. Just some thoughts.

 

[Dale Raby]

Got an idea that might work for some applications: The main issue seems to be the difficulty with X vs M synchronization. I had thought about trying to get something like an electronic flash unit from an old digital or sub-miniature film camera into the housing of a Minox flash gun for AG1 flash bulbs. Getting all the electronics into the unit should not be that big of an issue, but it would still have the synchronization problem. I suppose I could also get some magnesium, glass, and a vacuum pump, then contrive to make my own bulbs, but somehow I wonder how that would work out. One could also possibly contrive to use flash powder in an open pan... with potentially disastrous results on a camera held up to one's face.

The idea I came up with by-passes all these issues; just use an LED wired through a switch to a battery inside the Minox flash gun housing. You would turn it on, point it at your subject, adjust the shutter for the available light from what is essentially a miniaturized camera-mounted flashlight, and trip the shutter. It should work on any camera. As the aperture is always f/3.5, you would have to use your shutter speed instead of your aperture ring to adjust your exposure depending upon the distance from the subject to the light source (the LED). As the inverse square law applies to any fixed light source, coming up with an exposure chart in a dimly-lit room (where else would you need light?) shouldn't be all that difficult.

As infrared LED's are available, one could potentially contrive an infrared light source for use with infrared film and become a "real" spy.

I've been able to successfully use kerosene lamps and lanterns to make hand-held exposures, and an LED should be able to match an wick flame's illumination. I'll try to breadboard a circuit and give it a shot some time next month. As soon as Blue Moon processes my film, I should have a few experimental exposures.

 

[Helge]

You also flash is generally used at a shutter speed of 1/60 of a second. Most bulbs have a different color balance compared to electronic flash or LEDs. Bulbs also have a limited range compared to electronic flash or LEDs. Just some thoughts.

Even the smallest common bulbs have a GN of ≈ 40. So pretty respectable.

 

[AgX]

As Helge indicated the output of even the most tiny bulbs is huge. There is no way to miniaturize an electronic flash of same output into the casing of an incandescant flash.

By the way, that was not even the issue of the OP. He instead "just" wanted to contact an electronic flash to the socket for an incandescent bulb.
But even here we should not overlook that small flash bubs are at many places still easy available and cheap. His issue seems less that of economics than that of light control, I guess. More modern electronic flashes offer auto-exposure, even at several apertures.

 

[Dale Raby]

You also flash is generally used at a shutter speed of 1/60 of a second. Most bulbs have a different color balance compared to electronic flash or LEDs. Bulbs also have a limited range compared to electronic flash or LEDs. Just some thoughts.

Not necessarily though. A leaf shutter will sync at any shutter speed, but with a flash bulb, you will get a different exposure at faster speeds. As to color temperature, different flash units might have different color balances. Bulbs were either clear or blue, the blue ones being generally color balanced for daylight films. As to range, it depends upon the bulb (assuming you mean the distance from the light source to the subject). A GE #5 bulb gave a guide number of 200 with ASA/ISO 100 film. A #11 bulb was about a stop brighter (so about twice as bright). Most common hand-held flash units that I used in the seventies and eighties could not match that figure. If you are shooting B&W, color balance is less important and only has to be worried about with very technical work.

 

[John Koehrer]

Simple flash all the way up to pro flash did not use a delay for electronic flash they were strictly mechanical and not reliant
on power from the camera. Cameras that had F, M and X settings changed the delay by changing(reforming/bending)* the
internal contacts If you have a shutter with no contacts at all it's relatively simple. Two wires from the shutter housing to a hot
show or PC contact IF there is a delay in the camera the internal switch contacts can be adjusted(reformed/bent)* to close
when the aperture is fully opened.

* Bent is a couple of bucks. Reformed is FAR more expensive If you do things like this for a living