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11-14-2011, 09:14 AM   #1
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P-ttl

I understand that Pentax uses P-TTL which relies on a little pre-pulse from the flash. If you put a diffuser on the flash, does this impede with the camera's ability to set the flash level?

11-14-2011, 09:41 AM   #2
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QuoteOriginally posted by Spodeworld Quote
I understand that Pentax uses P-TTL which relies on a little pre-pulse from the flash. If you put a diffuser on the flash, does this impede with the camera's ability to set the flash level?
You are correct, the camera uses a preflash, but since the defuser will always be there there is not an impact in metering, because it uses the defused flash in teh metering as well.

the way P-TTL flash works, is that the camera meters the scene ambient light, and the impact that the pre flash has, both with open aperture. It then calculates the exposure required (i.e. flash duration) based upon what it reads back. All of this is done using the camera's standard metering and sensors
11-14-2011, 09:45 AM   #3
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OK. So, then, I take it if you have a diffuser on, it is likely that the output is raised as a result. Does that stand to reason?
11-14-2011, 10:47 AM   #4
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Yup that would make sense- but that would also be what you want to happen. The goal of the diffuser is to evenly distribute the light, not to weaken its intensity.


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11-14-2011, 10:55 AM   #5
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QuoteOriginally posted by Spodeworld Quote
If you put a diffuser on the flash, does this impede with the camera's ability to set the flash level?
No. Go ahead and use the diffuser.
11-14-2011, 11:20 AM   #6
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I would like to add a little here having used diffusers on both the onbourd flash and bigger flashes in P-TTL mode.


The camera meters before the pre flash then again with the pre flash. This pre flash is week. If you have a lot of dark stuff reflecting the pre flash it can make the flash brighter the you wanted. If the objects are to far away it can also fool the system. When you use a diffuser it will weaken the pre flash even more so the above problem can be a little more of a problem. In short you may have to use a little more control with the flash adjustments. But by all means use diffusers, its not like your going to break anything.


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