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Archive 2013 · TTL flash trigger
  
 
Image1
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p.1 #1 · p.1 #1 · TTL flash trigger


Could someone please explain the purpose of a TTL flash trigger, ..I am assuming it allows a hotshoe speedlite to still function at TTL Off Camera ..but the Flash is still triggered by the Camera! ..also what about a fill light or additional hair-light ...would they still be triggered ..but only function in Manual mode as slaves?


Jun 09, 2013 at 02:24 PM
BrianO
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p.1 #2 · p.1 #2 · TTL flash trigger


I use the Yongnuo YN-622C triggers for the Canon flash system. It allows remote Speedlites to function under radio triggering just as they would using the Canon Wireless system of optical triggering.

Under both systems, ETTL allows 3 Groups of Speedlites to be used off camera, so one could have, for example, a key light or lights on Group A, fill light(s) on Group B, and hair light(s) on Group C.

You'd set the ratio of key:fill + hair (Group C is a little different than A and B in how it is metered), and the camera would fire preflashes to measure and set the absolute output needed to achieve "proper" exposure within those ratios.

You can also set them for Manual power levels, and set each Group's power level independently.

The YN-622C requires newer Canon cameras that have flash control menus, because the radios have limited controls on the units themselves.

Non-TTL triggers will fire the lights from the camera, but the camera won't control the power levels; you'd do that manually, either at the lights or remotely depending on the system.



Jun 09, 2013 at 03:05 PM
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p.1 #3 · p.1 #3 · TTL flash trigger


Thanks BrianO


Jun 21, 2013 at 12:14 PM
cgardner
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p.1 #4 · p.1 #4 · TTL flash trigger


As background, the TTL radio triggers were created in response to the distance and line of sight limitations of the Canon and Nikon coded optical systems. The first to hit the market was Radio Popper, which piggyback on the Canon flashes converting and relaying the coded optical signals via radio. PocketWizards later came to market with a system which works directly off the signals normally transmitted to the flashes via the hotshoe from cameras which can control the flashes from the camera menu. Then the Chinese versions hit the market.

Canon finally switched to radio based triggering with the 600EX-RT but also made it backwards compatible with optically triggering, but user must select one or the other, not mix modes. There is also a new ST-E3RT radio controller for the hot shoe which is radio only when the photographer doesn't want a flash mounted on camera.

The camera makers opted for optical rather than radio initially because radio frequencies are regulated on an country-by-country basis and it's a logisitcal nightmare to get approvals. For example for the new Canon RT radio based system there is only a limited list of countries where they are legal to use even with the commonly used 2.4 GHz band.

Personally I never had any problems with the range of the Canon optical system for the type of shooting I do with speedlights (See http://photo.nova.org/CanonPracticalUsage/ ) so I never had a need for TTL radio triggers. For someone starting with speedlights now the 600EX-RTs, while seeming more expensive than other options are probably the best long term investment.



Jun 21, 2013 at 11:21 PM





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