Questions about LX flash sync.

*CSoars* · 03-03-2009, 08:07 PM

Just picked up an AF200T, as I wanted a 'compact' dedicated TTL flash with provisions for auto and manual control, in order to use it on my LX, MX, and off camera. I started to wonder if you could do slow speed sync by using auto or manual instead, as the X-sync lit up in the viewfinder of the LX no matter the selected speed on the shutter dial, and when I had the AF200T set on 'auto' and 'manual'

B. Dimitrov's site lists the LX's flash sync at 1/75th, nothing slower, nor bulb. The MX reads 1/60th~1, B, which I presume to read anything between 1/60th and 1 second, as well as bulb. In fact, all of the K, M and A bodies have this sync range, whether they be mechanical or electronic shutters.

Leonards Classic SLR site tries to explain the flash system here. I will quote some relevant bits from"Pentax LX - How does its metering works" and post my understanding below

TTL flashes:
"Set the flash unit to "TTL AUTO" operation and switch the unit "ON". Leave the camera's shutter dial set to "Automatic" and the camera will automatically set the shutter speed at "X" (1/75 second) for flash synchronization and illuminate the viewfinder LED at "X" as a visible "ready light." In addition to "Automatic" the camera's shutter speed dial may also be set at "X" for TTL operation."

Conclusion: syncs only at 1/75th

Non-Dedicated
"How about non-dedicated Flash ? Don't worry, since this camera is designed for the Pros, the LX system also offers you the unique option of synchronization even with non-dedicated electronic flash units with the shutter dial set at "Automatic". In addition, manual speeds from "X" through "B" may be used. On "Automatic" the synchronization range is between 1/30th second and 4 seconds."

Conclusions: Should work with 1-pin flashes, and the 3-pin AF200T set to AUTO or MANUAL. The X sync will light up as a 'flash charged' indicator, and the shutter will trip at any manually selected speed below X sync.

FINAL CONCLUSION: Slow speed sync should be possible with the LX as long as TTL is not used.

Do I have it right?

*Wheatfield* · 03-03-2009, 10:02 PM

yup

more cha

artobest · 03-04-2009, 12:54 PM

Fantastically useful, thanks. Now I can use my old Sunpak with its folding reflector umbrella.

But why does my LX overexpose with my AF280T?

And another question: does Exposure Compensation work as normal when using a flash?

*Wheatfield* · 03-04-2009, 03:09 PM

Originally Posted by artobest

Fantastically useful, thanks. Now I can use my old Sunpak with its folding reflector umbrella.

But why does my LX overexpose with my AF280T?

Do you have film in it?

And another question: does Exposure Compensation work as normal when using a flash?

If I recall correctly, it adjusts the flash exposure.

*CSoars* · 03-04-2009, 04:01 PM

But I also read that no matter the mode, 3 pin' dedicated' pentax flashes lock the sync @ 1/75th, even if used in auto; you need to cover one of the pins or use the big flash grip for the 400T that has a slow sync switch on it.

So 1 pin 3rd party flashes allow slow sync on auto, 3 pin pentax flashes lock it at 1/75th on auto. arrrg!

*Wheatfield* · 03-04-2009, 04:55 PM

Originally Posted by CSoars

But I also read that no matter the mode, 3 pin' dedicated' pentax flashes lock the sync @ 1/75th, even if used in auto; you need to cover one of the pins or use the big flash grip for the 400T that has a slow sync switch on it.

So 1 pin 3rd party flashes allow slow sync on auto, 3 pin pentax flashes lock it at 1/75th on auto. arrrg!

Sorry, I haven't thought about this for sometime.
If you are using a dedicated flash, the LX will not fire the flash unless there is more than approximately one stop of underexposure measured by the ambient light meter.
I'm pretty sure the LX won't fire any flash if underexposure is not indicated.
You have to cover one of the pins (I don't recall which one, sorry) to disable the auto shutter speed setting on the LX with a dedicated flash.

The LX was not built for fill flash.....