Light modifiers are bounce cards, diffusers, umbrellas, light spheres, etc. Where I could imagine the problem is that the pre-flash systems only send out a very small pop to determine exposure. The situation becomes somewhat like when you try to meter past the capability of the meter - like old stop down - so the pre-flash is small and the light modifier cuts 3 stops of light and the little pop didn't put out 3 stops to begin with. Now the reading would be incorrect and the main flash pop would be too strong. Not saying it would always happen, but I could imagine problems with some kinds of modifiers - especially the stronger diffusers.
In some situations, taking a shot and then looking at the histogram would work well. In wedding photography, that would mostly not work - you can't afford a test shot most of the time. -- Best regards, Bruce Monday, March 5, 2007, 9:48:31 AM, you wrote: GD> Not sure what you mean by "light modifiers" and how they would be any GD> different when using something that reads a P-TTL pre-flash and GD> something that reads the flash at exposure time. GD> I've had several dedicated TTL flash systems in the past. They had an GD> advantage when doing macro work or using filters as I had to do less GD> thinking about how to apply compensation for the light loss. But only GD> up to a point ... and that was with film. With digital preview, any GD> such situation is easily evaluated without even making an exposure. I GD> suspect that digital preview would have been a wonder when I was GD> using film SLRs... instant exposure feedback!!! for nothing!!! That's GD> what we used to waste hundreds of dollars on with polaroids ... :-) GD> Godfrey GD> On Mar 5, 2007, at 8:56 AM, Bruce Dayton wrote: >> My experience is somewhat similar, even though I do quite a bit of >> flash photography at weddings and events. If I am just doing daylight >> fill, then the AF360FGZ or AF540FGZ work very well as they can be >> dialed for compensation and support hi speed synch. Basically just >> dial in the amount of fill you want on the flash and start shooting >> just as if the flash wasn't there. >> >> When the flash is the primary light source, things change quite a bit. >> TTL or P-TTL on my *istD were fairly inconsistent. Not that I >> couldn't get a usable image, but that I couldn't get consistent >> exposure - usually underexposed. Since getting the K10D, I have shot >> two weddings using the AF400T in auto mode and have gotten a much >> better exposure overall and fairly consistent. I do kind of wonder >> how well the AF540FGZ would do in comparison. >> >> There is one benefit to the TTL method, although I don't know how well >> the P-TTL would actually work - that is when using light modifiers - >> especially strong ones - the theory is that the light hitting the >> sensor is measured for the exposure. But some of the light modifiers >> can eat up 2-3 stops of light. Since the P-TTL is a quicker, weaker >> flash, I could see how it might get misread. Can't say that I have >> really experimented enough to know but I could see some problems. -- PDML Pentax-Discuss Mail List [email protected] http://pdml.net/mailman/listinfo/pdml_pdml.net
