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Forum: Flashes, Lighting, and Studio
04-11-2013, 09:43 AM
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It's not so simple. The adapter has to know two languages: blah-TTL and some-other-TTL.
We already see big companies (Metz, Sigma) with large research staff struggling with reverse-engineering one language.
I personally think whaterver-TTL is overrated. My 2 copies of AF540FGZ are used much less than my Sunpak 120J and Metz 54MZ.
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Forum: Flashes, Lighting, and Studio
04-10-2013, 02:40 PM
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Step 1 makes a big difference in the context of this discussion (optical slave triggered by the built-in flash), because the preflash strobe in step 1 triggers the slave. My point is: the time between when the slave is triggered and when the shutter is fully open is NOT in the range of milliseconds. This confirms Jonathan Mac's comment that "by the time the camera takes the shot the moment has already passed" (flash is not in sync).
If the slave flash is used at reduced power (say, 1/32), it may still have sufficient charge to fire again when the main flash triggers it in step 4. But the first (maybe the only) triggering during step 1 does nothing to the exposure.
I think because of the long duration of the red-eye reduction, people realize that something is about to happen, and try NOT to blink.
On the other hand, the preflash strobe startles people. They blink unconsciously.
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Forum: Flashes, Lighting, and Studio
04-10-2013, 01:44 PM
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Have you actually measured it? Or have you found the spec somewhere?
The time between the preflash strobe and the main flash is actually noticeable. Some people (my son included) react to the preflash strobe and thus likely close their eyes during the main strobe. For this reason, I don't use p-TTL mode for group photos.
In my non-scientific guesstimation, the time between the p-TTL preflash strobe and the main strobe is in the neighborhood of 1/50 sec. Note the sequence:
1. Flash fires preflash strobe.
2. Mirror raises.
3. Leading shutter fully opens.
4. Flash fires main strobe.
5. Trailing shutter closes.
How long do you think it takes for (2) and (3)?
Do this simple experiment: setup an optical slave flash, one that is "dumb" (can not ignore the p-TTL preflash strobe). Using the built-in flash to trigger the slave, take a photo in front of the mirror, with both the camera and the slave flash visible in the mirror. Check the photo to see which flash(es) fires during exposure.
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