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Old Jan 4, 2008, 8:28 PM   #1
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Hi everyone

I was using the canon 400D with 24-70mm f/2.8L lens.

For unknown reasons, I always get badly overexposed shots when I try to fill flash in daytime, if I use apertures < f/8. I don't have the same problem if I take the shot in lower light, or if I switch to f/8 or higher in the daytime.

I wanted to use f/2.8 to get the bokeh on my shots so I tried changing the ISO to 100, and then set the exposure to -2 and flash exposure compensation to -2 and I still get severely overexposed shots. I then whacked on the 430 EX speedlite, put a diffuser on it, set the flash exposure compensation to -3, and exposure to -2 and still get the severe overexposure.

Am completely lost on this one. Does anybody have suggestions on why this is happening?


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Old Jan 4, 2008, 8:59 PM   #2
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What mode is the 400D set to?
... hopefully not in Av (or any of the automatic mode)

Camera on "Manual" is best (but the flash fill will still be on automatic)
-> You control the ambient light with the -2..-1..v..+1..+2 EV scale (to the left) with the aperture/shutter combination
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Old Jan 4, 2008, 9:04 PM   #3
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this is going to be a toughie...coz there are lots of parameters. A sample shot would also help.

NHL would be spot on this one with u.

---->check ifu have the high speed sych mode or the FP mode. Else the camera is still going to shoot at 1/250 of a second no matter how bright the scene is

At f2.8 in bright light the shuitter speed is going to be around 1/2000 or something. But since (IF) the flash is set to normal ETTL auto, its going to make the shutter speed to 1/250 and obviously over exposing.

To use flash at normal mode(auto mode) u need to make sure the camera meters at shutter speed below 1/250 or shud i say above. i mean 1/250 or greater(1/200,1/100) which inturn means pushing the aperture up. Hence u were getting better shots at apertuer above f8

Also ur talking abt bokeh. @f2.8 the bokeh is going to be already good. Flash and bokeh would work hand in hand when pushing the aperture narrow(or higher Fnumber)

In short to use F2.8 and flash use te FP mode or high speed synch. Else u will have to use HIGHER Fnumber only.




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Old Jan 4, 2008, 9:33 PM   #4
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Yeap nymphetamine is also correct, make sure you have FP flash enable on the 430EX or the camera won't allow a higher shutter speed...
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Old Jan 4, 2008, 10:59 PM   #5
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thanks nymphetamine and NHL

not sure what FP is, but I was using Av mode and my settings for the Flash Sync in Av mode is auto...so i'm still not sure if this should be on or off or left on auto?

I deleted the pics straight away unfortunately (had to preserve memory card space for valuable fireworks photos) but they turned out like a normal photo which has its levels increased to 3.00 on PS

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Old Jan 5, 2008, 7:10 AM   #6
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jaykobe wrote:
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but I was using Av mode and my settings for the Flash Sync in Av mode is auto...so i'm still not sure if this should be on or off or left on auto?
Exactly what I thought...
In Av mode the camera will meter for the ambient light which is OK until the flash fire which add to the exposure hence overexposed your entire picture - That's why it work better for you when in lower light and/or smaller aperture because the "ambient" light is darker and the flash will then complement your exposure



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not sure what FP is
FP stand for Focal Plane shutter in older camera which has a faster sync speed than normal. Canon also call this mode High-Speed Sync which is enabled from the flash (the 3rd upper button from the left on the 430EX)
-> This will allow the camera to select higher shutter speed than 1/250s to let you use a larger f/2.8 opening on the lens and still keep the EV scale to the left in daylight so the flash can balance the whole exposure when it fired...
With your current setting i.e. 1/250s max and f/2.8 thereabout the normal exposure will be adequate, however when the flash fired it overexposed the whole thing - By putting the camera on manual you can select both the aperture and shutter speed (while leaving the flash on automatic) and varies your EV scale -2..-1..v..+1..+2
On Av you are stuck with what the camera pick for shutter speed which is always in the middle of the scale @ the ..v..
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Old Jan 5, 2008, 6:08 PM   #7
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thanks NHL

so in summary, I could still use Av mode but I'd have to allow the high speed sync on the speedlite correct?

what about the built in flash though? can I still be in Av mode if I don't use the speedlite?


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Old Jan 5, 2008, 9:33 PM   #8
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jaykobe wrote:
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so in summary, I could still use Av mode but I'd have to allow the high speed sync on the speedlite correct?
Correct; However, you'll be "stuck" with what the camera pick in Av as it exposes for the EV at the center, whereas is M you can vary the ambient fill as the flash will always expose the foreground correctly with E-TTL



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what about the built in flash though? can I still be in Av mode if I don't use the speedlite?
Someone can correct me, as I shoot with a MrkII which has no built-in flash, but I don't believe the small capacitor in the camera built-in flash can support the FP mode: In this mode the flash has to pulse with a low-intensity burst for a longer period of time to follow the shutter slit:
http://eosseries.ifrance.com/eosseri...k_synchfp.html
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