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12-24-2006, 05:15 PM   #1
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K10D flash questions from DSLR newbie

Hi,

The K10D is my first DSLR, although I've been using Pentax cameras for over 20 years. I now find myself with a few questions about flash operation with the K10D. I've also asked these over at DP Review, but thought I'd try here also...

1. I have mainly been taking flash photos indoors waiting for the fog to lift in the UK (it has been hanging around almost constantly since I bought the camera last week ). While the camera displays any flash exposure compensation, this does not seem to be something that is shown once downloaded into the Photo Browser s/w. I've tried a couple of other progs. also & none appear to show this either. Before I delete the images from the SD card, does anyone know how I can access this info. once downloaded, as I presume it must be somewhere in the EXIF data...?

2. Along a similar line, when setting flash exposure compensation on my AF-540FGZ flashgun, this information does not appear to be transferred to the camera (i.e. if I set +1.0EV comp. on the flashgun, the recorded image info. says 0.0EV flash comp., although the photos appear to have the compensation applied correctly, as far as I can see). Should I, therefore, just set any flash compensation via the camera's Fn menu instead?

Anyone else come across these 'problems'?

Cheers,
AJ

12-24-2006, 07:25 PM   #2
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Ivan Glisin's Avatar

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Interesting question. This is not direct answer (just my thoughts) but it may help:

P-TTL system works by applying internal flash compensation: camera meters reflected light during the preflash, then sends instruction to the flash to reduce power necessary to render the scene as middle gray. This is first compensation done by P-TTL system and is always negative relative to maximal power. It is used to change flash output power, and is not a post-processing trick. Let's call it power scaling factor (PWRSF) and assume 1 represents full power and less than that less power of course.

You can also set compensation on your flash unit and as in-camera setting (two values are added together!) to adjust value calculated by P-TTL system. Lets name them FCOMP and CCOMP. Again, it changes real power (no post processing).

Finally, since each flash has different maximal power (expressed as Guide Number) meaningful EXIF info that would include flash compensation must also include GN (similar to exposure compensation that includes Av, Tv and ISO so you know what actually got compensated).

So, EXIF with all this may read:

GN = 82
PWRSF = 0.786
FCOMP = -0.5
CCOMP = 0.0

Now, the question is: who would understand it and how could any software use it and for what? Although I don't see any harm in storing total flash compensation applied as a single parameter regardless of flash output power, someone was not quite sure it deserves to be in EXIF so we don't have it.
12-25-2006, 09:58 AM   #3
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Thanks for the detailed explanation on P-TTL flash!

QuoteOriginally posted by i.glisin Quote
Although I don't see any harm in storing total flash compensation applied as a single parameter regardless of flash output power, someone was not quite sure it deserves to be in EXIF so we don't have it.
...but...since flash compensation (for the internal flash) appears on the camera's LCD screen when displaying the photo(s), I presume it must be storing the data somewhere...and logically (to me at least!) that would be in the EXIF, would it not?

So, if it is not stored in the EXIF data, then I am curious as to where it is. And if it is in the EXIF, why is it not something that is shown by the Photo Browser software?

Cheers,
AJ
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