What triggers a wireless slave flash?

Discussion in 'Canon Accessories' started by kevsdad, Feb 28, 2013.

  1. kevsdad

    kevsdad TPF Noob!

    Joined:
    Feb 28, 2013
    Messages:
    3
    Likes Received:
    0
    Location:
    United States
    Can others edit my Photos:
    Photos OK to edit
    I have a Canon T3i and will be purchasing a 430EXii soon. What actually triggers the off-camera flash (430EXii)? The light from the internal flash or is there a transmitter in the camera (T3i) that only works when the internal flash is open? Reason I ask is I have an old Vivitar 285 that I could use as the primary flash, but it must use the shoe, either on-camera of off by means of a cable, leaving the internal flash unusable as it will not open if the shoe is occupied. Will the light from the 285 trigger the off-camera 430 to fire or does the internal flash have to do that? Thanks.


     
  2. tirediron

    tirediron Watch the Birdy! Staff Member Supporting Member

    Joined:
    Jul 8, 2005
    Messages:
    44,108
    Likes Received:
    13,837
    Location:
    Victoria, BC
    Can others edit my Photos:
    Photos OK to edit
    To use the built-in (TTL capable system) you will need to have your pop-up flash up; it communicates (via line-of-sight only) with the slave flashes using a series of virtually invisible micro-flash bursts which are "read" by the IR receiver on your slave flash. Some flashes have a built-in slave cell (that is, they will detect the flash of another speedlight and trigger themselves), and your version of the 285 may be one of them, in which case you could have it anywhere that it could "see" the light from your camera's pop-up flash and it would work, BUT you will be limited to manual flash only.

    There are althernatives. You can get a optical slave "foot" which a speedlight will attach to, or you can use radio triggers.
     
  3. Mully

    Mully TPF Noob!

    Joined:
    Jul 23, 2012
    Messages:
    3,066
    Likes Received:
    788
    Location:
    Mt Ulla, NC
    Can others edit my Photos:
    Photos OK to edit
    RF units work very well and you can buy one for $30-40 on ebay
     
  4. KmH

    KmH In memoriam Supporting Member

    Joined:
    Apr 9, 2009
    Messages:
    41,401
    Likes Received:
    5,696
    Location:
    Iowa
    Can others edit my Photos:
    Photos OK to edit
    Infrared (IR) light from the camera is used to not only trigger the off-camera flash unit, the IR light can also communicate with the of camera flash.

    Since it is light it is limited in range, particularly in direct sunlight because sunlight also includes interfering IR light, and pretty much to line-of-sight.

    After market radio frequency (RF) triggers are very popular because they have a lot more range, can transmit through walls and around corners, and are not affected by sunlight.
     
  5. Tiberius47

    Tiberius47 TPF Noob!

    Joined:
    Oct 4, 2007
    Messages:
    742
    Likes Received:
    47
    Can others edit my Photos:
    Photos NOT OK to edit
    It's a series of coded light pulses sent from the flash on the camera. It is NOT infra red light, since you can see the light pulsing from the camera's flash easily. It is visible white light. The pulses have encoded information that tells the slave flash when to fire and how strong to fire.
     
  6. kevsdad

    kevsdad TPF Noob!

    Joined:
    Feb 28, 2013
    Messages:
    3
    Likes Received:
    0
    Location:
    United States
    Can others edit my Photos:
    Photos OK to edit
    Thank you all for your help!
     
  7. TCampbell

    TCampbell Been spending a lot of time on here!

    Joined:
    Mar 31, 2012
    Messages:
    3,607
    Likes Received:
    1,551
    Location:
    Dearborn, MI
    Can others edit my Photos:
    Photos OK to edit
    BTW, you can trigger a remote flash either wired or wireless. If wireless it can be visible light or IR or radio.

    But in the case of YOUR camera ... the T3i's pop-up flash is using visible light (not radio or IR). You can add a radio module for more reliable triggering (line of sight isn't necessary) but you need both a radio transmitter and a radio receiver (there are versions that can support Canon E-TTL or you can get significantly less expensive radios that just do "manual" flash (you have to manually use the controls on the back of your 430EX II to tell it how much power to use when firing. It wont automatically be calculated for you like it is in E-TTL mode). You can also buy Canon's commander module (speedlite transmitter ST-E2 for IR) which would let you fire the flash without using the pop-up flash.
     
  8. KmH

    KmH In memoriam Supporting Member

    Joined:
    Apr 9, 2009
    Messages:
    41,401
    Likes Received:
    5,696
    Location:
    Iowa
    Can others edit my Photos:
    Photos OK to edit


    The camera's flash is not capable of only emitting IR light. The invisible to humans IR flash communication signal is part of the visible light the flash unit creates.
    The detector in the slave flash units only detects the IR portion of the light the camera's built-in flash unit creates.

    Canon's ST-E2 also uses IR light, because that is the light frequency range the slave or eTTL capable flash units can detect. See the ST-E2 specifications: http://www.usa.canon.com/cusa/consu...up/speedlite_transmitter_st_e2#Specifications
    The same applies to Nikon's slave/iTTL capable flash units and the Nikon SU-800.
     
    Last edited: Mar 3, 2013

Share This Page