[Lord Lucan]

Today I set up some flash equipment [electronic] that would be triggered with a PC sync lead. To test the set-up I picked up my LX (which had neither film nor batteries in it), set the shutter speed to X, and fired some shots.

However, on a whim, I had plugged the sync lead into the FP socket rather than the X socket on the LX body. The flash did not fire. I then changed to the X socket and the flash did fire.

I understood that the only difference between the FP (for focal plane bulbs) and the X (for electronic flash, X for "xenon") sockets was that the FP contacts are made when the first shutter curtain starts to move (ie is still shut) and the X contacts are made when it stops (ie fully open).

So why did my flash not fire through the FP socket? Is my LX FP function faulty (not that FP matters these days) or am I missing something?

[Lhorn]

I can’t answer your question but am interested in the answer. If anyone can explain the difference between the two flash sockets I’d appreciate it. Thanks

[stevebrot]

I understood that the only difference between the FP (for focal plane bulbs) and the X (for electronic flash, X for "xenon") sockets was that the FP contacts are made when the first shutter curtain starts to move (ie is still shut) and the X contacts are made when it stops (ie fully open).

That sounds right, though there might be a few quirks in regards to fine points. For example, on the Spotmatic and K-series bodies, while the contacts for FP and X sync are triggered separately, there is a dependency relationship between the two. I will have to research that more fully and whether it carried over to the LX.

If anyone can explain the difference between the two flash sockets I’d appreciate it. Thanks

LL's understanding is correct, but the full explanation is a little more involved. The Wikipedia article is helpful...

Flash synchronization - Wikipedia


Steve

[stevebrot]

For example, on the Spotmatic and K-series bodies, while the contacts for FP and X sync are triggered separately, there is a dependency relationship between the two. I will have to research that more fully and whether it carried over to the LX.

So why did my flash not fire through the FP socket? Is my LX FP function faulty (not that FP matters these days) or am I missing something?

On the Spotmatic and K-series bodies, the FP switch must be closed in order for the X sync to fire. As a result, wear or maladjustment of the FP contact will result in failure of both FP and X sync. Of course, that has nothing to do with the lack of FP on your LX. Short answer...I am of no help here!


Steve