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Change Camera ISO or Flash FEC

HI Everyone
I always trying to gain insight on using On Camera Flash to the more  effective way. 
Im trying to understand.  When I shoot flash indoor bouncing off walls .When is it more effective  to increase Camera ISO  ( For example 1600 ISO to 3200 ISO ) or change the Flash FEC  to + 1.00 for example .Thank for your help Im trying to wrap my noodle around this concept.

Lou Recine


  • TrevTrev Moderator
    Hi Lou,

    If indoors, you need a higher ISO to help light up the ambient/room light, obviously you know, so you need to consider how much background/ambient light you need for starters, that's it, it's that simple.

    Then, you just need to adjust you flash power to correctly expose your subject/s with that background being what it is.

    1600 to 3200 ISO is, as you know, only 1 stop, but that 1 stop of extra ambient could be a big difference in helping out with flash power, especially if you are already nearly maxed out on your flash.

    Don't forget, there is a bonus if you shoot in Manual Mode on your Nikon, you can then use the Camera Body's Exposure Compensation along with your FEC since Nikon (only in manual) Bodied Cameras use the body compensation (ambient light) to help force the flash to discharge more power.

    eg: You have say 3200 ISO, 125th, f2.8 and you also have FEC with +3/ev, but still not enough light on subject, if you then put the actual camera body's exposure compensation to say +2.0/ev, it forces the flash to dump more power, giving it a +5.0/ev instead of having to put the flash in manual mode and forcing it to dump power up to Full.

    Caveat: This only works on Nikons, Manual Mode, Flash in iTTL.

    Quite simple to be honest, get background right, then use flash to correct subject exposure and if you are already at +3.0/ev on flash, and if you don't like going up high ISO and exposure not right, just force flash via the Camera Body's Exposure Compensation option.

    Oh, don't forget, next time you shoot, and you wonder why you are over-exposed with iTTL flash even at -3.0/ev, check your camera body, it will have body compensation exposure on for sure, drop it back to 0.

    One thing, I've never tried it using the -/ev on camera body, be interesting to see.


    Merry Xmas mate! :)
  • Neil vNNeil vN Administrator
    "When is it more effective  to increase Camera ISO  ( For example 1600 ISO to 3200 ISO ) or change the Flash FEC  to + 1.00 for example"

    You need to understand that these two settings affect things very differently. 

    Changing your ISO will change your sensor's sensitivity, and will affect both ambient exposure and the flash's reach. However, changing the ISO will (in theory) not change your flash exposure. The ISO will only (in theory) affect your flash exposure if you are outside of the range of what the flash is capable of. Then bumping your ISO will have effect your flash exposure. 

    Changing your FEC will affect your TTL flash exposure and give you more juice ... assuming you are within the capability of the flash's potential output. 
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