RonFrank
Contributor
I posted this in response to another thread, but certainly worth a standalone thread.
Here is the difference between iTTL, and dTTL (you asked)
D-TTL uses a five-element flash sensor and looks at the shutter curtain for reflections. One problem is that it sees outside the 1.5x area on the DSLRs. D-TTL pre-flash is a sequenced series of 18 pulses from the flash. Only one flash can be used if you're in a D-TTL mode.
I-TTL uses the 1005-element color matrix meter in the viewfinder and has much better ability to distinguish what's happening in specific area of the frame. I-TTL pre-flash has been extended to allow communication between flashes and camera so that multiple flash (up to 10), groups of flash (up to 3 groups of 3 flashes), and wireless exposure control of flashes is all possible.
What does this all mean? iTTL has a LOT of extended capabilities, and also is fooled less often due to a much more comprehensive pre-flash sequence, and much better and well defined metering area. It allows TTL BETWEEN flashes, and better yet, one can control flash ratio's AND it's wireless.... Really cool STUFF!!
Does it work better UW. I'm not certain anyone can answer unless they are using a flash housing as Ikelite is about to release the first UW iTTL flash. Will those flashes support the full iTTL implementation with wireless multiple flash capabilities, and the master to slave control that is available on the Nikon SB800?? God only knows, or maybe Ikelite.
I can tell you iTTL with even one flash works better on land vs. dTTL in SOME situations. One thing to keep in mind is that as advanced as these things get, if you use manual mode, and have the flash exposure dialed in based on distance, it is repeatable, and right on. This will apply UW as well as on the surface assuming constant lighting, constant subject distance, and constant water clarity.
Where dedicated TTL with a flash really helps is when everything is changing, subject distance, lighting, and when it works, it works damn well, and it DOES work for the majority of subjects.
However the BEST photographer is one who uses their skill and mind, and is NOT totally dependent upon technololgy, and pushing a button to get an exposure. Let's face it, if you are in a situation where iTTL is NOT working, or even the Camera exposure meter (which as these TTL meters are based on the same technology, they are fooled by similar subjects), you either loose the shot, or rely on your knowledge and understanding on how to shoot manual.
IMO anyone who is shooting a multiflash setup UW BETTER take the time to become a photographer. If you are spending 5K and do not have time to even learn how to use the equipment, well IMO THAT is VERY pathetic!!!!
Here is the difference between iTTL, and dTTL (you asked)
D-TTL uses a five-element flash sensor and looks at the shutter curtain for reflections. One problem is that it sees outside the 1.5x area on the DSLRs. D-TTL pre-flash is a sequenced series of 18 pulses from the flash. Only one flash can be used if you're in a D-TTL mode.
I-TTL uses the 1005-element color matrix meter in the viewfinder and has much better ability to distinguish what's happening in specific area of the frame. I-TTL pre-flash has been extended to allow communication between flashes and camera so that multiple flash (up to 10), groups of flash (up to 3 groups of 3 flashes), and wireless exposure control of flashes is all possible.
What does this all mean? iTTL has a LOT of extended capabilities, and also is fooled less often due to a much more comprehensive pre-flash sequence, and much better and well defined metering area. It allows TTL BETWEEN flashes, and better yet, one can control flash ratio's AND it's wireless.... Really cool STUFF!!
Does it work better UW. I'm not certain anyone can answer unless they are using a flash housing as Ikelite is about to release the first UW iTTL flash. Will those flashes support the full iTTL implementation with wireless multiple flash capabilities, and the master to slave control that is available on the Nikon SB800?? God only knows, or maybe Ikelite.
I can tell you iTTL with even one flash works better on land vs. dTTL in SOME situations. One thing to keep in mind is that as advanced as these things get, if you use manual mode, and have the flash exposure dialed in based on distance, it is repeatable, and right on. This will apply UW as well as on the surface assuming constant lighting, constant subject distance, and constant water clarity.
Where dedicated TTL with a flash really helps is when everything is changing, subject distance, lighting, and when it works, it works damn well, and it DOES work for the majority of subjects.
However the BEST photographer is one who uses their skill and mind, and is NOT totally dependent upon technololgy, and pushing a button to get an exposure. Let's face it, if you are in a situation where iTTL is NOT working, or even the Camera exposure meter (which as these TTL meters are based on the same technology, they are fooled by similar subjects), you either loose the shot, or rely on your knowledge and understanding on how to shoot manual.
IMO anyone who is shooting a multiflash setup UW BETTER take the time to become a photographer. If you are spending 5K and do not have time to even learn how to use the equipment, well IMO THAT is VERY pathetic!!!!