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04-26-2012, 10:58 PM   #1
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Pentax LX slow sync options?

Hi,
I've read thru the threads here and I've seen mentioned two options to get slow sync on the LX -

1. Covering one of the pins on the hot shoe (I don't know which one though)
2. Buying the tall Pentax Grip which DOES have a switch on it to allow slow sync.

My question is, does the Pentax Grip really allow the LX in paricular to do slow sync? If so, it seems odd that the AF400T flash does NOT have this switch.

I also read that the LX will NOT fire a flash unless it detects greater than one stop underexposure of ambient light which would seem to mean that you could NEVER use the ttl flash mode for contrast control. For example if it is possible to move your shutter down to 1/4 second @ f11 for a particular scene while the flash was connected..then if that shutter/aperture combo was the "correct" exposure, the LX would STILL not fire the flash because no underexposure was detected. You would have to move the settings to 1/4 sec @ f16 in the same light, thereby underexposing a stop and then the LX would fire the flash, which would end up being dominant in the scene because the TTL would balance out overall exposure of which the flash would be the greatest contributor. Am I thinking of this correctly? So, is there no way just to lighten the shadows in a TTL mode on the LX even after jumping thru all of those hoops?

If all of the above is true, then what good would the "slow sync" switch on the Pentax Grip do for the LX really?

04-27-2012, 06:36 AM   #2
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I found flash control to be the Achilles Heel of the LX, and so never used it with portable flash. It was fine in the studio, but as noted, when light levels were in the fill flash range, it wouldn't fire the flash.
I ended up using K1000s for wedding work and leaving the LX in the bag for studio work.
04-27-2012, 07:49 AM   #3
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QuoteOriginally posted by Wheatfield Quote
I ended up using K1000s for wedding work and leaving the LX in the bag for studio work.
The same controls you apply to flash with the K1000s (manual mode only) can be applied to the LX.
04-27-2012, 08:10 AM   #4
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QuoteOriginally posted by LesDMess Quote
The same controls you apply to flash with the K1000s (manual mode only) can be applied to the LX.
I could never get them to fire the flash is there was more than a one stop difference in ambient light. In a backlit situation, the thing wouldn't fire the flash. Didn't matter if I was in manual or auto (in fact I pretty much never used auto). This applied to all three of my LX bodies, so it wasn't that I had one with a random flaw.

04-27-2012, 05:16 PM   #5
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uh oh, so, still some confusion in the responses! I wish there was some definitive answer...but it's looking like the LX for contrast control just won't fire the flash..
04-27-2012, 09:56 PM   #6
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I just tried my LX set in auto aperture and a AF280T set to TTL mode, the LX detects the AF280T and X (1/75) is lit. If the scene detected is higher then X then the flash won't fire. If the scene detected is lower then X, the flash will fire. Move the AF280T switch to "M" and X is no longer lit and the flash will fire each and every time regardless of meter reading. Put my non-TTL flash like the Vivitar 283 and the same as the AF280T in manual mode - X is not lit and it will fire each and every time.
04-27-2012, 10:18 PM   #7
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Thanks

QuoteOriginally posted by LesDMess Quote
I just tried my LX set in auto aperture and a AF280T set to TTL mode, the LX detects the AF280T and X (1/75) is lit. If the scene detected is higher then X then the flash won't fire. If the scene detected is lower then X, the flash will fire. Move the AF280T switch to "M" and X is no longer lit and the flash will fire each and every time regardless of meter reading. Put my non-TTL flash like the Vivitar 283 and the same as the AF280T in manual mode - X is not lit and it will fire each and every time.
Thanks Les..
So I think the conclusion is no TTL in slow sync, but slow sync works in manual or automatic flash modes below sync speed...
04-27-2012, 10:36 PM   #8
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To be sure, in TTL mode, the LX detects that based on the scene lighting, aperture and shutter speed that it does not warrant flash. If you want the flash to fire, that must assume you want the LX to overexpose the scene by some amount. In which case, you can therefore set the compensation adjustment according to how much overexposure you want. From what I just tested, this is about a stop over. If the scene being metered for example is a face that is strongly backlit, then this is most likely appropriate to "equalize" the scene. Of course if you are using negatives or b&w, most of them will tolerate considerable overxposure (>3) and still be completely normal.

04-28-2012, 05:18 PM   #9
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My understanding is that the LX only fires the flash if the ambient exposure for the selected aperture is X-sync or slower (otherwise you don't get full flash coverage). As the X-sync is only 1/75th this is a problem for fill flash in bright ambient conditions.
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