On Camera TTL and Manual Off Camera Flashes in Softbox(s)
Just learning OCF technique and shopping for a lighting system / trigger system.
Cactus comes highly recommended.
My question is "How does the pass-through TTL for on camera flash actually work?"
The question behind the question is "Should I get a system that offers TTL control of my remote flashes?"
I shoot with Nikon D610 & D7100.
I have a few flashes: SB-400, SB-600, SB-700, Metz 58 AF-2, and just for fun an old Vivitar 2800 Auto Thyristor that I don't use. and expect to buy more - looking a Godox bare-bulb systems like their 360ii or 600's which come under a variety of brand names.
Cactus comes in currently at about $130 (CDN) each these units would set me back $390 to run two Off Camera Flashes + one on camera in TTL.
Pocket-Wizard TT5 Flex set of three units with controlling gizmo comes is at $655 (CDN imported from B&H) or $750 if I buy the same thing here in Canada. P-Wiz does not promise compatibility with my Metz (although I've hit a few samples of people shooting Metz with P-Wiz TT5 Flex so I'm hopeful). Cactus says it is compatible - I trust that it is. But with P-Wiz I get TTL.
For less than the Cactus system I can get TTL from Godox with their X1 system. But lose the super-compatibility feature of the Cactus.
My typical situation is a speedlight (or two) in a softbox as main light and another as a backlight or kicker, or in a snoot or whatever highlight I choose, plus the on-camera flash (which may be a bit off camera on a bracket with a connecting cord)
With Cactus, only the on-camera unit is TTL. The others are manual.
So - How on earth does the camera's TTL system take into account the effect of the off camera flashes. Even if it is somehow smart enough to know these other O.C. flashes exist through the settings on the trigger, how would it know how they are positioned, how close to the subject and the affect of any light modifier?
This has me asking what the point of an on camera TTL would be. Makes perfect sense in a one flash set up with the flash on camera as the meter goes T.T.L - through the lens. But once you start getting creative with the off camera lights then what?
So how does this TTL metering work with OC manual flash(es) ?
And how might that influence the decision about off camera TTL?
Please be patient if this is such a novice question - I need a big "L" on the back of my camera as I'm just a learner still.
Fort Kent, AB