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11-25-2015, 11:16 PM   #16
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QuoteOriginally posted by mcgregni Quote
The flash compensation limits on the older 'Mk1' Pentax flashes are -3.0 - +1.0 stops ..... the newer MkII models have extended this to -4.0 - +2.0, a total of 7 stops adjustment.
Interesting to know, thanks.

Does this mean that maximum P-TTL power is two stops below the maximum 1/1 manual power level, or does it mean that sometimes using positive exposure compensation has no effect?

QuoteOriginally posted by mcgregni Quote
if '20-30' is not enough, what would you suggest is a fair average figure, considering that I'm not referring to any specific product?
As you don't refer to a specific product, why don't you give a range that covers all products?
I'd say "20m-100m" would be fair.
Even though some triggers can do well over 100m, it seems to me that "100m" is large enough to be not considered a practical limitation by the vast majority of readers.

QuoteOriginally posted by mcgregni Quote
... you are free to move your flashes, with the modifiers on, closer to and further from the subject, in order to play creatively with the light qualities, but WITHOUT AFFECTING YOUR ESTABLISHED FLASH EXPOSURE,
This is a very good point in the context of using one light source.

In the presence of multiple light sources, I would want only the light that I'm moving to adjust in power accordingly, however the P-TTL approach implies that all lights are affected. P-TTL will maintain the lighting ratios, meaning that all light levels are adjusted by the same factor. I don't think that's what you want in most cases. Say you are moving the key light closer to make it softer. In this case you only want to decrease the key light power a bit, but leave rim light, hair kicker, background light, etc. at the same levels.

Of course one can adjust by changing the overall compensation, but it that means that there is a need for manual intervention, as opposed to the one light scenario where P-TTL truly takes away the need to adjust a setting due to a subject to light distance change.

11-26-2015, 03:45 AM   #17
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With a ratio set there's no reason for all the flashes to adjust their automatic output. Moving one, say the main light, closer for that softer look, would only cause the system to auto-adjust the unit that was moved .... The system aims to keep the same global flash EV with the same fixed ratio (plus any compensations dialed in). These will hold the desired contrast effect. The single unit being moved will auto-adjust to maintain the exact same contrast effect and total EV ... There's no reason for the second, say the 'fill' unit, to need any manual intervention.

I'll include your new suggestion for radio trigger ranges in the next edition of the guide, thanks.


Regarding the P-TTL and manual power/compensations steps, clearly the manual ones represent directly the actual power extremes. The P-TTL 'stops' are not fixed outputs, but are a fixed differential value (1 'stops worth ' of light) away from a variable start point (the metered flash EV). It is the metered flash EV itself that will determine the practical limitations of the maximum compensation limits, so this varies between scenes and situations. If your metered EV is only 1 stops worth of light below the flashes maximum possible output, then the 1 stop compensation is as much as you can get out of it .... Any additional plus input has no further effect.

Last edited by mcgregni; 11-26-2015 at 03:57 AM.
11-26-2015, 03:57 AM   #18
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QuoteOriginally posted by mcgregni Quote
Moving one, say the main light, closer for that softer look, would only cause the system to auto-adjust the unit that was moved ....
Have you verified this claim with an actual experiment?

I'd say is it nigh on impossible for the system to respond in the manner you expect it to because it should not have any concept of which part of the metered light comes from which flashgun unless it fired all pre-flashes serially.
11-26-2015, 03:59 AM   #19
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QuoteOriginally posted by rod_grant Quote
Well done, Nigel.
This forum is a great source for help, from lots of members.
BUT you have gone the extra step.

Thanks! I appreciate that, and I hope the guide and discussions have been helpful, and a bit of flashy fun as well !

---------- Post added 26-11-15 at 11:05 ----------

QuoteOriginally posted by Class A Quote
Have you verified this claim with an actual experiment?

I'd say is it nigh on impossible for the system to respond in the manner you expect it to because it should not have any concept of which part of the metered light comes from which flashgun unless it fired all pre-flashes serially.

I have seen this in practice, yes, but always keen to have an excuse to mess around more! I'm out at the moment and then its work, but I'll run some tests as soon as possible. There is a good amount of documentation on the Canon ratio system (I'm reading a book at the moment that talks about it), and it works serially , with individual pre -flashes in sequence, so its possible the Pentax system works the same .... ? Of course, we DON'T have any documentation. !!


Last edited by mcgregni; 11-26-2015 at 04:06 AM.
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