[pathdoc]

In these modern days of X-sync flash, we all well know that the default is for the flash to fire when the leading curtain has finished opening (we're talking single-discharge here; no high-speed sync tricks).

For trailing curtain sync, AFAIK or can reason from first principles, it fires such that the burst is complete just before the second curtain begins to close.

Now, what about those old FP flashes? The ones which maintained such a long peak burst that according to the camera manuals, you could sync them at higher speeds than X sync (depending on the nature of the flash).

It seems to me that the timing there is that if the first curtain opens at time = 0, the FP flash must fire at some time zero minus T milliseconds, such that the output has time to plateau and provide an even exposure across the duration of the first/second curtain slit travel.

That being the case, if I hooked up a very simple X-type (electronic) flash to the FP port of one of my film cameras and fired it, there is every chance that the discharge would be over before the first curtain even began its travel (and one should get a dead frame). And if not, one would get a very wide band of first curtain across most of the frame with a slit of light indicating where the last part of the X-flash discharge was occurring.

In fact, if one knew the discharge duration, one could use the proportion of the frame exposed to calculate the timing of the FP port.

Are there any old-time users of FP-type flashes who can cast light (pun intended) on this?

[RKKS08]

I am not sure I remember correctly, as I sold my Exakta (VX1000) together with the manual end of 1981.

This camera hat 2 ports, marked X and M. The contacts for M were closed immediately with pressing the shutter, the contacts for X (electronic flash) with a delay of 1/20 sec. So for this camera the time between pressing the shutter and fully opened curtains was 1/20 sec (at least at the recommended flash exposure time of 1/60 sec of this camera).

I also think there were bulbs with a drawing of the light intensity curve over time outside on the package.

EDIT: Maybe you can find some information in the Pentax LX manual (or books about the LX!) regarding the timing.

[WPRESTO]

I had early Pentax bodies with FP sync PC sockets and also an early electronic flash. As you speculated, if an electronic flash is connected to the FP socket, the flash fires fully before the shutter starts to open. As I think you guessed, flashbulbs take time to reach peak output, and have a roughly bell-shaped curve. The curve for FP bulbs was long and low, with a rather gradual rise and fall. M-class bulbs had a much faster rise to a higher peak, and a much shorter output duration.

[pathdoc]

True, but the M class bulbs still fired from the FP ports, yes?

[WPRESTO]

True, but the M class bulbs still fired from the FP ports, yes?

I cannot offhand remember if they were supposed to be fired via the FP or the "X" socket.

[wombat2go]

I cannot offhand remember if they were supposed to be fired via the FP or the "X" socket.

The Pentax MX manual, page 18, gives a tabulation of Falsh bulb types, connection, and allowable shutter speeds.
Was the MX the last Pentax with FP capability?

Here is a page showning brightness vs time curves of various flash bulbs:
Cress Photo - Flashbulbs.com

Regards!

[WPRESTO]

The Pentax MX manual, page 18, gives a tabulation of Falsh bulb types, connection, and allowable shutter speeds.
Was the MX the last Pentax with FP capability?

Here is a page showning brightness vs time curves of various flash bulbs:
Cress Photo - Flashbulbs.com

Regards!

My first flash gun was a huge Kalart unit that used C-cell batteries and took screw-base bulbs. It was designed for use on press-type 4X5 cameras. As I recall, the first bulbs I used were S-type. The FP bulbs I used later in a fan-fold flash gun that had a hot-shoe base (but my Pentax did not have a hot shoe) were similar to the small bayonet-base bulbs shown on page 6 of the website you posted, with that low-long output curve. Still later I used AG-1 bulbs, and finally a little Braun 2-AA electronic flash that I still use, primarily because it has a very simple AC connection (wire with no transformer box) and when so powered it recycles very quickly. A much later Sunpak 444 flash I still use also has an AC cord, with a big transformer box at the AC plug, but the recycling when the cord is used is no faster than with fresh batteries.

[wombat2go]

My first flash gun was a huge Kalart unit that used C-cell batteries and took screw-base bulbs.

Was it like the Graflite shown below on the Speed Graphic?

I have non destructively modified this one to hold a little old electronic flash.

For many years I used the Pentax AF160 on a LPL bracket as shown on the Pentax MX.
The AF160 had a socket for cable directly to the X socket on the Pentax cameras.
(although in this photo it is on a remote hotshoe.)
The LPL bracket was the cure for red-eye, compared to having the flash on the camera hotshoe, too close to the lens.

On the left of the Graflex is a Pentax AF500FTZ used as a slave.
As far as I know it was the first Pentax flash with stand-alone slave capability.
However the AF500FTZ has no control functionality with any of the Pentax dslrs, not even the early ist series.

[pathdoc]

Was the MX the last Pentax with FP capability?

Pictures of the later LX clearly show an FP socket. Clearly (at least at the time the design was finalised) there must still have been a large supply of bulbs, either ongoing production or vast new old stock, and photographers using them.

I know that in 1979, I was using 10 shot flashbulb strips (glorified banks of flashcubes) on my parents' Polaroid instant camera, so the flashbulb era was by no means over then. Whether the LX's FP port was a concession to those photographers who still held a large stock and desired/preferred to use them or whether it reflected an expectation of ongoing use, I cannot say.

[WPRESTO]

Was it like the Graflite shown below on the Speed Graphic?

Yes, the Kalart I had was similar, same big. blindingly shiny reflector, same aluminum stem, but a slightly different slide-on clamping design. I had an L-bracket for mounting the flash on a camera smaller than a Graflex press (the flash gun is long gone, but I think I still have the L-bracket). The flash had a mechanical cable release that plugged into a two-hole socket at the side. There was a box-like structure at the plunger + plug that had a wheel that could adjust the trip-delay of the flash relative to the shutter. Listening carefully you could here something inside the box snapping back by spring force when the plunger reached a certain point. Turning the wheel changed the point of plunger travel at which that internal mechanism was released and closed the flash-triggering circuit.

[leekil]

Well, when the LX came out, flashbulbs were still readily available. Not sure exactly how who used them vs. electronic flashes, though.

In general, flashbulbs are/were more powerful than an electronic flash; so there might have been situations where they were preferable to illuminate a large area.

[WPRESTO]

Well, when the LX came out, flashbulbs were still readily available. Not sure exactly how who used them vs. electronic flashes, though.

In general, flashbulbs are/were more powerful than an electronic flash; so there might have been situations where they were preferable to illuminate a large area.

And also, the X-sync speed on the LX was really low, even for the time. Easy to imagine situations where you would get ghosting. But with FP (and some other bulbs) you could use 1/500.