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trouble with canon flash in ttl mode with a 200mm lens ?

Mo4753Mo4753 Member
edited October 2012 in news & discussions
I was playing around at a friends wedding taking some photos with a 5d mk 2 and 70-200 f4 with a 580ex in the hot shoe.

When I use a lens with a shorter focal length, the ttl usually lights the entire frame evenly. But in this case, the subject was well lit but everything around them a bit too dark.

I would have imagined the auto mode of ttl would understand I need more reach using a longer lens and sent more light out of the flash.

Any comments or suggestions would be appreciated.

Thank you.


  • Mo4753Mo4753 Member
    edited September 2012
    Here is an example straight out of camera. I would have liked a little more light around the subject
  • looks like a typical on camera flash shot to me the background dosnt look unaturally dark considering the on camera 580, do u have an example of when the background is more illuminated at a shorter focal lengnth?
  • this one was shot with a 50mm f1.4 iso 800 f4 1/50th sec canon 580ex in hotshoe in ttl mode
    Although the first shot looks great as a portrait of the child, I wanted more of the environment lit up in the background so the viewer can tell it was at a party etc.
  • TrevTrev Moderator
    I don't think it has anything to do with focal length per se, just that at a longer focal length, you have filled the frame more with the kid, and the flash has compensated for it.

    But, of most interest, it's to do with what your actual ambient settings were, if you had your ambient around 1+ stop under, then of course it's going to be dark around the edges merely because the flash has only lit the kid.

    The surrounds looked dark only because of the ambient settings. OR . . . you used a mode, and the camera took into consideration of the main amount of light on the kid and shut it down anyway before more of the ambient could register.

    Were you in manual or another mode with camera settings.

    Was the flash bounced or direct? The second shot looks direct, could be wrong, only going by the very small pinpoint of light and the harsher shadows under chins compared to a big softer bounce.

    Also the second shot only appears to show more of the surrounds because of the lighter background there anyway, but it's still under-exposed than say a correct ambient exposure. Of course it's a good shot as is, background is not intrusive.

  • I appreciate your comments. You have reminded me that I need to take into account my shutter speed to have more control over the ambient light in the exposure. I didnt want to shoot slower than 1/50th sec to prevent camera shake.But I probably could have raised my iso from 800 to 1600 and had better results.

    In these photos, I felt I was too far from anything white to bounce the flash off, so I put a stofen cup on the flash and tilted the flash head slightly forward and down.

    I think I may have solved the problem as to why the environment around the subject was darker that what i would have liked.

    Usually I work outdoors without a flash. I want someones face to be exposed properly so I use spot metering on the face. At this party I was in spot metering mode as I forgot to switch it back to evaluative metering.
  • yes the difference btwn the 2 photos appears to only be a difference of shutterspeed the first one being a faster shutterspeed thereby not allowing much ambient light to lighten the background the second photo there is alot more ambient in the exposure due to the 1/50 sec, exposure. also note that at iso 1600, 1/50 of a sec u r more likely to have ghosting/camera shake than when shooting at iso 800.
  • I am a Nikon shooter, and using the sb800 in ttl, the head adjusts to send the beam according to the focal length used. Using a wide angle will understandably sends a wide beam to illuminate the frame, doing so light bounces from walls etc to compensate ambient. However, shooting at 200mm, flash only needs to illuminate that frame using a narrow beam. My flash only goes up to 105mm. One can over ride this focal length and use 25mm to shoot 200mm to gets wider beam. Exposing for ambient is important in any case to get the sought for exposure.
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